GOM 07. Guideline for Inspection of GECOL Equipments

[GOM 08] Ver 1.0 : July 1, 2007

Guideline For Inspection of Materials

GECOL General Department of Distribution

Guideline for Inspection of Materials

[ Table of Contents ]

I. Power Transformer................................................................. - 1 -

1. General ..............................................................................................................- 2 - 1.1 Description.............................................................................................................- 2 - 1.2 Types of power transformer...................................................................................- 2 - 1.3 Structure.................................................................................................................- 4 - 1.4 Rating.....................................................................................................................- 4 - 1.5 Aging deterioration and maintenance of power transformer .................................- 5 -

2. Delivery and storage.........................................................................................- 7 - 2.1 Delivery .................................................................................................................- 7 - 2.2 Storage ...................................................................................................................- 8 -

3. Inspection ..........................................................................................................- 9 - 3.1 Field inspection after operation at normal loading ................................................- 9 - 3.2 Daily inspection ...................................................................................................- 10 - 3.3 Routine inspection ...............................................................................................- 15 - 3.4 Special inspection ................................................................................................- 19 -

4. Test method .....................................................................................................- 19 - 4.1 Oil testing ............................................................................................................- 19 - 4.2 Insulation resistance measurement ......................................................................- 26 - 4.3 Test on on-load tap-changer.................................................................................- 29 -

II. Gas Insulated Switchgear..................................................... - 35 -

1. General ............................................................................................................- 36 - 1.1 Description...........................................................................................................- 36 - 1.2 Structure (Cubicle type GIS) ...............................................................................- 36 - 1.3 Rating...................................................................................................................- 37 -

2. Delivery and storage.......................................................................................- 37 - 3. Inspection ........................................................................................................- 37 -

3.1 Field inspection before operation ........................................................................- 38 - 3.2 Daily inspection ...................................................................................................- 39 - 3.3 Routine inspection ...............................................................................................- 39 - 3.4 Special inspection ................................................................................................- 41 -

III. Circuit Breakers.................................................................... - 45 -

1. General ............................................................................................................- 46 - 1.1 Description...........................................................................................................- 46 - 1.2 Types of medium voltage circuit breaker ............................................................- 46 - 1.3 Rating...................................................................................................................- 49 - 1.4 Consideration for safety practices .......................................................................- 49 -

2. Delivery and storage.......................................................................................- 50 - 2.1 Delivery ...............................................................................................................- 50 -


2.2 Storage .................................................................................................................- 51 - 3. Inspection ........................................................................................................- 51 -

3.1 Medium voltage circuit breakers .........................................................................- 51 - 3.2 Low voltage circuit breakers ...............................................................................- 54 -

4. Test methods....................................................................................................- 55 - 4.1 Contact resistance test..........................................................................................- 55 - 4.2 DC Hi-pot test for vacuum bottles.......................................................................- 55 -

IV. Disconnecting Switches ........................................................ - 61 -

1. General ............................................................................................................- 62 - 1.1 Description...........................................................................................................- 62 - 1.2 Rating...................................................................................................................- 62 - 1.3 Consideration.......................................................................................................- 62 -

2. Delivery and handling ....................................................................................- 67 - 2.1 Delivery ...............................................................................................................- 67 - 2.2 Unpacking............................................................................................................- 67 - 2.3 Assembly and rigging ..........................................................................................- 68 -

3. Inspection ........................................................................................................- 68 - 3.1 Field inspection before operation ........................................................................- 68 - 3.2 Routine inspection ...............................................................................................- 69 -

V. Surge Arrester ....................................................................... - 72 -

1. General ............................................................................................................- 73 - 1.1 Description...........................................................................................................- 73 - 1.2 Types of surge arrester .........................................................................................- 73 - 1.3 Structure...............................................................................................................- 75 - 1.4 Rating...................................................................................................................- 76 - 1.5 Classifications of surge arrester ...........................................................................- 76 - 1.6 Ground resistance value of surge arrester............................................................- 77 -

2. Delivery and storage.......................................................................................- 77 - 3. Inspection ........................................................................................................- 77 -

3.1 Substation class arrester.......................................................................................- 78 - 4. Test method .....................................................................................................- 80 -

4.1 Megger test ..........................................................................................................- 80 - 4.2 Leakage current test .............................................................................................- 80 - 4.3 Infrared analysis...................................................................................................- 81 -

VI. Storage Batteries ................................................................... - 84 -

1. General ............................................................................................................- 85 - 1.1 Description...........................................................................................................- 85 - 1.2 Types of storage battery.......................................................................................- 85 - 1.3 Nickel-Cadmium Cell Batteries...........................................................................- 87 - 1.4 Structure (Vented nickel-cadmium cell battery)..................................................- 89 -


1.5 Requirements for nickel-cadmium batteries ........................................................- 89 - 2. Delivery and storage.......................................................................................- 92 -

2.1 Delivery ...............................................................................................................- 92 - 2.2 Storage .................................................................................................................- 92 -

3. Inspection ........................................................................................................- 93 - 3.1 Initial inspection ..................................................................................................- 93 - 3.2 Routine inspection ...............................................................................................- 93 - 3.3 Special inspection ................................................................................................- 94 -

4. Test methods....................................................................................................- 95 - 4.1 Tools and devices.................................................................................................- 95 - 4.2 Visual inspections of batteries .............................................................................- 96 - 4.3 Connection resistance measurement..................................................................- 100 - 4.4 Capacity tests .....................................................................................................- 100 -

5. Charging of nickel-cadmium batteries .......................................................- 101 - 5.1 Battery charging precautions .............................................................................- 101 - 5.2 Charging of nickel-cadmium batteries...............................................................- 102 -

6. Placing a new battery in service ..................................................................- 103 - 6.1 Placing nickel-cadmium batteries in service. ....................................................- 103 - 6.2 Connections for batteries ...................................................................................- 104 -

7. Replacement of a battery .............................................................................- 104 -

VII. Battery Charger .................................................................. - 107 -

1. General ..........................................................................................................- 108 - 1.1 Description.........................................................................................................- 108 - 1.2 Types of battery chargers...................................................................................- 108 - 1.3 Rating.................................................................................................................- 109 - 1.4 Battery charging requirement ............................................................................- 109 - 1.5 Accessories for battery chargers ........................................................................- 110 -

2. Inspection ...................................................................................................... - 111 - 2.1 Routine Inspection .............................................................................................- 111 -

VIII. Protective Relays................................................................. - 113 -

1. General .......................................................................................................... - 114 - 1.1 Description.........................................................................................................- 114 - 1.2 Type of relay ......................................................................................................- 114 -

2. Delivery and storage..................................................................................... - 115 - 3. Inspection and test ........................................................................................ - 115 -

3.1 Field inspection before operation ......................................................................- 115 - 3.2 Inspection and test for solid-state relays............................................................- 116 -

4. General requirements for test...................................................................... - 118 - 4.1 Circuit burden measurements for CTs ...............................................................- 118 - 4.2 Grounding CT and PT circuits...........................................................................- 119 - 4.3 Open-secondary circuits ....................................................................................- 119 -


5. Test records ................................................................................................... - 119 -

IX. Grounding Inspection......................................................... - 120 -

1. General ..........................................................................................................- 121 - 1.1 Description.........................................................................................................- 121 - 1.2 Purpose of grounding.........................................................................................- 121 - 1.3 Safety precautions while making ground tests ..................................................- 121 - 1.4 Standard of grounding resistance.......................................................................- 123 -

2. Inspection ......................................................................................................- 123 - 2.1 Inspection after installation................................................................................- 123 - 2.2 Routine inspection .............................................................................................- 124 -

3. Testing method..............................................................................................- 124 - 3.1 When grounding wire is not connected to neutral .............................................- 124 - 3.2 When a grounding wire is connected to system neutral ....................................- 127 -

4. Reducing ground resistance.........................................................................- 128 - 4.1 Methods of getting optimum ground resistance ................................................- 128 - 4.2 Constructing a chemical for reducing earth resistivity ......................................- 128 -

X. Pole ....................................................................................... - 133 -

1. General ..........................................................................................................- 134 - 1.1 Description.........................................................................................................- 134 - 1.2 Type of poles......................................................................................................- 134 - 1.3 Characteristics of poles......................................................................................- 134 - 1.4 Consideration.....................................................................................................- 135 -

2. Handling and storage ...................................................................................- 136 - 2.1 Concrete pole .....................................................................................................- 136 - 2.2 Wood pole..........................................................................................................- 137 -

3. Inspection ......................................................................................................- 139 - 3.1 Concrete pole inspection....................................................................................- 139 - 3.2 Wood pole inspection ........................................................................................- 139 -

4. Wood pole reinforcement .............................................................................- 143 - 4.1 Stub pole ............................................................................................................- 144 - 4.2 Steel reinforcing ................................................................................................- 145 - 4.3 Compound set methods......................................................................................- 146 -

5. Recommendations.........................................................................................- 147 - 5.1 Concrete pole inspection results ........................................................................- 147 - 5.2 Wood pole inspection results .............................................................................- 148 -

XI. Insulator............................................................................... - 151 -

1. General ..........................................................................................................- 152 - 1.1 Description of insulator .....................................................................................- 152 - 1.2 Types of insulator ..............................................................................................- 152 -

2. Deliver and storage.......................................................................................- 154 -


3. Inspection ......................................................................................................- 154 - 3.1 Interval of detection...........................................................................................- 154 - 3.2 Inspection method..............................................................................................- 155 - 3.3 Results ...............................................................................................................- 157 -

4. Cleaning of insulators...................................................................................- 157 - 4.1 Interval of insulator cleaning .............................................................................- 158 - 4.2 Insulator cleaning method..................................................................................- 159 - 4.3 Results ...............................................................................................................- 164 - 4.4 Technical considerations for energized cleaning with water.............................- 164 -

XII. Distribution Transformer................................................... - 173 -

1. General ..........................................................................................................- 174 - 1.1 Description.........................................................................................................- 174 - 1.2 Types of distribution transformer ......................................................................- 174 - 1.3 Structure.............................................................................................................- 175 - 1.4 Rating.................................................................................................................- 175 -

2. Delivery and storage.....................................................................................- 176 - 2.1 Delivery .............................................................................................................- 176 - 2.2 Storage ...............................................................................................................- 176 -

3. Inspection ......................................................................................................- 176 - 3.1 Field inspection before operation ......................................................................- 176 - 3.2 Daily inspection .................................................................................................- 177 - 3.3 Routine inspection .............................................................................................- 177 -

XIII. Power Capacitor Banks...................................................... - 181 -

1. Generals.........................................................................................................- 182 - 1.1 Description.........................................................................................................- 182 - 1.2 Types of power capacitor...................................................................................- 182 - 1.3 Structure.............................................................................................................- 183 - 1.4 Rating.................................................................................................................- 183 - 1.5 Application ........................................................................................................- 183 - 1.6 Capacitor unit capabilities .................................................................................- 184 - 1.7 Considerations ...................................................................................................- 184 -

2. Handling ........................................................................................................- 186 - 3. Inspection ......................................................................................................- 187 -

3.1 Initial inspection ................................................................................................- 187 - 3.2 Routine inspection .............................................................................................- 187 - 3.3 Special inspection ..............................................................................................- 188 -

4. Test method ...................................................................................................- 188 - 4.1 Insulation resistance measurement ....................................................................- 189 - 4.2 Capacity test ......................................................................................................- 189 -

XIV. Step Voltage Regulator ....................................................... - 192 -


1. General ..........................................................................................................- 193 - 1.1 Description.........................................................................................................- 193 - 1.2 Rating.................................................................................................................- 193 - 1.3 Structure (Single-phase voltage regulator by Cooper electric company) ..........- 194 -


3. Inspection ......................................................................................................- 195 - 3.1 Field inspection before operation ......................................................................- 195 - 3.2 Routine inspection .............................................................................................- 195 - 3.3 Special inspection ..............................................................................................- 196 -

XV. Auto Recloser ...................................................................... - 199 -

1. General ..........................................................................................................- 200 - 1.1 Description.........................................................................................................- 200 - 1.2 Types of auto-recloser........................................................................................- 200 - 1.3 Structure (Model: GVR by Whipp and Bourne)................................................- 201 - 1.4 Rating (Model: GVR by Whipp and Bourne)....................................................- 202 -

2. Delivery and storage.....................................................................................- 203 - 3. Inspection ......................................................................................................- 203 -

3.1 Field inspection before operation ......................................................................- 203 - 3.2 Routine inspection .............................................................................................- 204 -

4. Test method ...................................................................................................- 205 - 4.1 Operating test.....................................................................................................- 205 - 4.2 Battery test .........................................................................................................- 205 - 4.3 Vacuum interrupter contact test.........................................................................- 207 -

XVI. Ring Main Unit ................................................................... - 212 -

1. General ..........................................................................................................- 213 - 1.1 Description.........................................................................................................- 213 - 1.2 Type of RMU.....................................................................................................- 213 - 1.3 Structure (Example: Model CN2/SN6 Type).....................................................- 214 - 1.4 Rating.................................................................................................................- 215 - 1.5 Protection system...............................................................................................- 215 -


3. Inspection ......................................................................................................- 216 - 3.1 Field inspection before operation ......................................................................- 216 - 3.2 Routine inspection .............................................................................................- 217 -

4. Gas sampling and filling ..............................................................................- 219 -

XVII. Distribution Box,LV Panel, Pillar Box, Fuse Box ............ - 221 -


1. General ..........................................................................................................- 222 - 1.1 Description.........................................................................................................- 222 - 1.2 Rating.................................................................................................................- 223 -

2. Inspection ......................................................................................................- 225 - 2.1 Daily inspection .................................................................................................- 225 - 2.2 Routine inspection .............................................................................................- 225 -

XVIII. Diesel Generator ................................................................. - 228 -

1. General ..........................................................................................................- 229 - 1.1 Structure.............................................................................................................- 229 - 1.2 Instruction..........................................................................................................- 230 - 1.3 Consideration.....................................................................................................- 231 -

2. Delivery and handling ..................................................................................- 233 - 3. Inspection ......................................................................................................- 233 -

3.1 Weekly inspection .............................................................................................- 233 - 3.2 Routine inspection .............................................................................................- 235 -

XIX. Public Lightning.................................................................. - 239 -

1. General ..........................................................................................................- 240 - 1.1 Description.........................................................................................................- 240 - 1.2 Types of public lighting circuits ........................................................................- 240 - 1.3 Multiple type lighting system components........................................................- 240 - 1.4 Luminaires .........................................................................................................- 240 - 1.5 Lamp types ........................................................................................................- 240 - 1.6 Characteristics of lamps.....................................................................................- 241 - 1.7 Luminaire components ......................................................................................- 242 - 1.8 Multiple type lighting controls ..........................................................................- 243 -

2. Inspection ......................................................................................................- 243 - 2.1 Interval of inspection .........................................................................................- 243 - 2.2 Inspection method..............................................................................................- 244 -


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I. Power Transformer


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1. General

1.1 Description Power transformer is defined as a static piece of apparatus with two or more windings which, by electromagnetic induction, transforms a system of alternating voltage and current into another system of voltage and current usually of different values and at the same frequency for the purpose of transmitting electrical power.

In a distribution substation, power transformers provide the conversion from sub-transmission circuits to the distribution primary. Most are connected delta-grounded wye to provide a ground source for the distribution neutral and to isolate the distribution ground system from the sub-transmission system.

Power transformer used in station can range from 5MVA in smaller rural substations to over 80MVA at the urban stations (base ratings). Stations with two banks, each about 20 MVA, are common. Such a station can serve about six to eight feeders.

Power transformers have multiple ratings, depending on cooling methods. The base rating is the self-cooled rating, just due to the natural flow to the surrounding air through radiators. The transformer can supply more load with extra cooling turned on. Normally, fans blow air across the radiators and/or oil circulating pumps

1.2 Types of power transformer

1.2.1 Dry type power transformer

Dry type transformers depend primarily on air circulation to draw away the heat generated by the transformer’s losses. Air has a relatively low thermal capacity When a volume of air is passed over an object that has a higher temperature, only a small amount of that object’s heat can be transferred to the air and drawn away. Liquids, on the other hand, are capable of drawing away larger amounts of heat. Air cooled transformers, although operated at higher temperatures, are not capable of shedding heat as effectively as liquid cooled transforms. This is further complicated by the inherent inefficiency of the dry type transformer. Transformer oils and other synthetic transformer fluids are capable of drawing away larger quantities of excess heat.


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Dry type transformers are especially suited for a number of applications. Because dry type transformers have no oil, they can be used where fire hazards must be minimized. However, because dry type transformers depend on air to provide cooling, and because their losses are usually higher, there is an upper limit to their size (usually around 10,000 kVA, although larger ones are constantly being designed). Also, because oil is not available to increase the dielectric strength of the insulation, more insulation is required on the windings, and they must be wound with more clearance between the individual turns.

Dry type transformers can be designed to operate at much higher temperatures than oil tilled transformers (temperature raises as high as 150ºC). Although oil is capable of drawing away larger amounts of heat, the actual oil temperature must be kept below approximately 100ºC to prevent accelerated breakdown of the oil.

Two of the advantages of dry-type transformers are that they have no fluid to leak or degenerate over time, and that they present practically no fire hazard. It is important to remember that dry type transformers depend primarily on their surface area to conduct the heat away from to core. Although they require less maintenance, the core and case materials must be kept clean. A thin layer of dust or grease can act as an insulating blanket, and severely reduce the transformer’s ability to shed its heat.

1.2.2 Oil immersed transformer

Oil immersed transformers are capable of handling larger amounts of power. The oil transfers the heat away from the core more effectively than air. The oil can also be routed away from the main tank, into radiators or heat exchangers to further increase the cooling capacity.

The oil also acts as an insulator. Since oils will break down and lose their insulating ability at higher temperatures, oil immersed transformers are designed to operate at lower temperatures than dry types (temperature rises around 55 ºC). Just as with dry types, oil immersed transformers can be self cooled, or they can use external systems to augment the cooling capacity.

A self-cooled transformer depends on the surface area of the tank walls to conduct away the excess heat. This surface area can be increased by corrugating the tank wall, adding fins, external tubing or radiators for the fluid. The varying heat inside the tank creates convection currents in the liquid, and the circulating liquid draws the heat away from the core. The cooling class designation for self-cooled, oil-filled transformers is ONAN.

Fans are often used to help circulate the air around the radiators. These fans can be


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manually or automatically controlled, and will increase the transformer’s kVA capacity by varying amounts, depending on the type of construction. The increase is usually around 33 percent, and is denoted on the transformer’s nameplate by a slash. Slash ratings are determined by the manufacturer, and vary for different transformers. If loading is to be increased by the addition of pumps or fans, the manufacturer should be contacted. The cooling class designation for a forced air-cooled, oil immersed transformer is ONAF.

1.3 Structure

Dry type power transformer Oil immersed power transformer

1.4 Rating

1.4.1 Dry type power transformer

Rated power (MVA) Rated voltage ratio

(kV) AN AF Tap changing

10 12.5 NLTC 30/11

20 25 NLTC


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1.4.2 Oil immersed power transformer

Rated power (MVA) Rated voltage ratio

(kV) ONAN ONAF Tap changing

20 25 OLTC

25 31.5 OLTC

32 40 OLTC 66/30

40 50 OLTC

5 - NLTC

7.5 - NLTC

10 12.5 OLTC

12.5 16 OLTC

16 20 OLTC

66/11

20 25 OLTC

5 - NLTC

7.5 - NLTC

10 - OLTC

12.5 - OLTC

30/11

20 - OLTC

1.5 Aging deterioration and maintenance of power transformer

Service life of transformer depends on the condition of its used materials such as conductive, magnetic, insulating, and structural material, etc. Especially when a insulating material is in process of deterioration, there are many cases that not only invasion of abnormal voltage or inflow of large fault current result in occurrence of fault for destruction of insulation but slight voltage variation or load increase also does.

1.5.1 Aging deterioration of power transformer

Aging deterioration of parts of power transformer mainly depends on the deterioration of a insulating material of a conduct forming winding or spacer between coils, and insulating oil. And the causes of the deterioration of them would be as follows.


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1.5.1.1 Deterioration by heat

Service life is the most influenced at the maximum peak temperature and it will decrease in proportion to an exponential function as the temperature becomes high. This is fundamentally attributable to heat resolution of an insulating material, and in result mechanical intensity becomes decrease.

1.5.1.2 Deterioration by moisture absorption

It is closely connected with an insulating breaking voltage of a solid one of insulating materials. It makes not only insulating resistant power deteriorated, but also mechanical intensity dropped by speeding heat deterioration of a solid insulating material up.

1.5.1.3 Deterioration by oxygen absorption

Acid value increases when insulating oil became oxidized through reaction with oxygen and this is continued deterioration of insulating material. And this increase of acid value makes sludge and reduces a cooling effect. In addition, the intensity of solid insulating material becomes deteriorated when it contacts with oxygen and is oxidized, especially this tendency is distinguished as its temperature becomes high.

1.5.1.4 Deterioration by partial discharge of electricity

A partial discharge of electricity occurs when the intensity of an electric field to the internal of transformer exceeds a certain limit or when an insulating material has defect. Partial discharge of electricity in the condition of normal operating voltage makes an insulating material eroded, carbonized and insulating resistant power deteriorated.

But in general, partial discharge of electricity is very rare in the condition of normal operating voltage. Instead, it breaks out very open when an insulating material has a defect.

1.5.1.5 Deterioration by mechanical stress

An insulating material is destructed mechanically and its insulating resistance power is deteriorated by electro-mechanical power or movement which is produced by a external short or excess current.

1.5.1.6 Influence of light


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Ultraviolet rays among light expedites the deterioration of insulating oil. Therefore insulating oil should not be exposed to light.

1.5.1.7 Mixture of a different kind insulating oil

There are many kinds of insulating oil. Stability becomes different according to the degree of refining of them though same kind insulating oil are mixed, needless to say different kind one.

1.5.1.8 Contact reaction of metals

Such Metals of transformer as an iron core, winding, steel for case, copper, etc accelerate the oxidization action of insulating oil.

1.5.1.9 Mutual influence of insulating material

Insulating materials for an iron core and winding influence deterioration of insulating oil, and especially insulating varnish is most.

These causes of deterioration make the flashing point of insulating oil lowered, its coefficient of viscosity increased, cooling action not smoothed, specific gravity increased, acid value increased, and dielectric strength deteriorated. Also they make the mechanical and dielectric strength of an insulating material deteriorated. Deterioration of both insulating oil and materials bring about trouble. Heat is the most influenced cause among the causes of deterioration of insulation, and additionally moisture absorption and oxidization expedite it.

2. Delivery and storage

2.1 Delivery When unloading the transformer or placing it in position, be sure to use the designated lifting eyes or jacking points, the transformer should be handled in the normal upright position, and in no case should it be tilted more than 15 degrees. Spreaders should be used to hold the lifting cables apart, particularly if they are short and may bear against external assemblies or bushings. Do not attempt to lift or drag the transformer by placing a loop or sling around it, and do not use radiators, bushings, or other auxiliary equipment for


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climbing or to lift the transformer. Transformers are extremely dense and heavy, much heavier than circuit breakers or other switchgear items. A conservative safety factor should always be applied when a transformer must be lifted.

2.2 Storage Regular inspection and documentation procedures should be conducted during transformer storage. All inspection and service procedures should be thoroughly documented, and any discrepancies or adverse conditions should be noted. Pumps and fans should be operated for 30 minutes, once a month. At the end of the storage period, oil samples should be drawn and analyzed for dielectric strength, power factor, and water content. Insulation resistance and power factor tests should be conducted on the transformer and compared to the original factory data.

2.2.1 Short-term storage

Follow these steps to store transformer up to three months.

(a) Set the transformer on a firm, level foundation.

(b) Ground the tank and any bushings that have been installed.

(c) Store the transformer in dry air on nitrogen if oil filling is impractical.

NOTE: Dry air may not be used for storage periods exceeding three months. Storing transformers without oil requires that positive gas pressure be maintained continuously.

(d) Install gas-pressure regulating equipment after the transformer has been delivered, received, and inspected.

CAUTION: Before opening the gas valve connecting the nitrogen regulator to the transformer tank, set the gas regulator to 2 psig.

NOTE: Transformers not normally equipped with gas-pressure regulating equipment can use the upper oil-filling connection for temporary hose connections.

(e) Install a vacuum/pressure gauge where it can be easily read by workers positioned at ground level.

2.2.2 Long-term storage


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When the unit is to be stored for more than 3 months, it should be protected from the weather. All scratches or paint defects should be touched up before storage. If the transformer is filled with oil, it should be tightly sealed so that no moisture or air can enter the case. If the transformer is shipped filled with inert gas, periodic inspection should determine that a positive pressure of about 2 psi is maintained at all times. Water-cooled transformers should have the water-cooling coils filled with alcohol or other similar antifreeze to eliminate any danger of freezing or contamination.

Larger transformers are often shipped without oil. They are vacuum filed with hot oil at the factory to impregnate the winding insulation with oil. The oil is then removed for shipping. This oil impregnation is vital to the winding’s insulation strength, and will be lost if the transformer is stored for too long without oil. Most manufacturers recommend a maximum storage tie of 3 months without oil. If this storage time is exceeded, hot oil vacuum degasification must be performed, and the manufacturer’s guidelines should be followed.

A transformer may be stored for long periods of time (over three months), if it is filled with oil.

Follow these steps to store transformers over three month.

(a) Place the transformer on a firm, level foundation.

(b) Install nitrogen equipment.

(c) Check the transformer for leaks using the procedure given previously.

(d) Fill the transformer with dry, degassed oil.

(e) Check the nitrogen pressure as described previously.

(f) Connect the control cabinet heater to control condensation.

3. Inspection

3.1 Field inspection after operation at normal loading After 1 week of operation at normal loading, inspect the following items.

3.1.1 Dry type transformer

(a) Perform infrared scan and compare with temperature gage, if any.


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(b) Check temperature gage, if any, and compare with nameplate rating.

(c) Check loading and compare with nameplate rating.

3.1.2 Oil immersed transformer

(a) Conduct in-depth inspection of transformer and cooling system, check for leaks and proper operation.

• Oil pumps load current, oil flow indicators, fans, etc • Transformer tank • Oil level gages • Pressure relief • Dissolved gas analysis

(b) Do IR scan of transformer cooling system, bushings and all wirings.

(c) Test all controls, relays, gauges; test alarms and annunciator points.

(d) Inspect transformer bushings.

• Check with binoculars for cracks and chips • Look for oil leaks and check oil levels • Do IR scan

(e) Inspect pressure controls if you have a nitrogen over oil immersed transformer.

(f) Inspect pressure gage.

3.2 Daily inspection Daily inspection of power transformer shall be performed in the process of patrol through regular visual checking a transformer. • Read and record the indicators provided on the transformer. • These values should be compared with the values obtained previously to detect for any

abnormalities. • During the inspection, pay attention to any abnormalities such as noises, irregular

vibration, discolorations, smoke etc.

3.2.1 Transformer temperature

(a) Check and record the oil and winding temperature.


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(b) Record ambient temperature, load and voltage.

NOTE1: The transformer temperature directly affects the life of the insulating material.

NOTE2: The maximum temperature rise limits are specified for both oil and winding temperature. During the daily inspection, check not only that temperatures are within the maximum limit, but also that these temperatures lie within a satisfactory range by comparing their values with the test results in the test report, load conditions and ambient temperature.

3.2.2 Oil level

(a) Check and record the level of oil shown by the oil level indicator.

(b) Check that the glass of oil level indicator is not dirty.

3.2.3 Noise

(a) Check for any abnormal sound and vibration etc.

NOTE: Learn by hearing an average & regular sound; If an irregular noise is heard, compare with remembered normal sound and further investigation should be done immediately.

3.2.4 Oil leakage

(a) Check for oil leaks at any connections such as valves, meters and particularly welding points.

3.2.5 Breather

(a) Pay attention to the discoloration of the silica gel.

(b) Check the level of the sealing oil in oil cup.

3.2.6 Pressure relief

(a) Check for cracks, damages and traces of oil overflowed from the pressure relief device.


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3.2.7 Cooling equipment

Check for cracks, damages and traces of oil overflowed from the pressure relief device.

3.2.8 On load tap changer

(a) Check for operating sounds.

(b) Check whether the tap position is correct or not.

(c) Record the number of tap changing operations.

(d) Check the oil level gauge of OLTC conservator.

3.2.9 Off-circuit tap changer

(a) Do not operate tap changer when the transformer is energized.

3.2.10 Bushing

(a) If the bushing is provided with oil level gauge, check oil level and oil leaks.

(b) Check visually the extent of any contamination on the bushing.

(c) Check the over heat of terminals.

3.2.11 Buchholz relay

(a) Check whether it is filled up with gas.

3.2.12 Loose connections and valves

(a) Check for any loose connections such as connectors main circuits, grounding circuits, auxiliary circuits, foundation bolts and the like.

(b) Valves are vulnerable to vibration. These should be checked particularly carefully.

3.2.13 Gas leakage

(a) In the case of N2 gas sealed transformer, measure the nitrogen gas pressure and check


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for gas leaks.

3.2.14 Instrument

(a) Check indictors and relays.

3.2.15 The others

(a) Abnormal exciting noise and vibration.


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Table 1 Details of daily inspection

Item of inspection Point of inspection

Surrounding temperature

Oil temperature

Winding temperature

1st , 2nd current

- Comparison with prior record,

surrounding temperature

- Operation of ventilation in transformer room,

cooling equipment, thermometer

Nitrogen gas pressure - Comparison with oil temperature – pressure curve

- Operation of pressure gauge

Oil level - Comparison with oil temperature

Noise and vibration - Abnormal allophone

Oil leakage - Valve, protective equipment against heat,

welding part, packing joint, etc

Tap changer of oil filter - allophone in operation, frequency and time

Of operation, pressure for filtration, sliding, etc

Terminal overheating - Discoloration of thermo tape

Bushing - Oil leakage, discoloration, crack, stain, etc

Oil preservation, respiration

equipment,

- Oil level, nitrogen gas pressure, degree of discoloration of moisture

absorbent, smooth action of respiratory equipment

Cooling equipment - Operation of fan and oil pump,

indication of flow meter, Indication of oil gauge,

heat switchboard, valve block, etc

Relay or mechanical protective

device - Operation

Painting - Rust occurrence

Bolt - Allophone by vibration

Control box - Operation of Heater in control panel

status of packing, frost

Arrestor, grounding wire - Discoloration, crack, stain, operation frequency,

condition of connection and supporting


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3.3 Routine inspection This is inspection carried out periodically in condition that the operation of power transformer is stopped and its outside case is not open. This inspection includes the measurement of insulating resistance of main and control line, conditions of insulating substance, gas analysis and bushing cleaning, tightness of terminal, operation test of protective device, visual inspection.

From the historical information obtained during these inspections and the operating condition, the time of the periodic inspections may need to be increased or could be decreased.

3.3.1 Interval of inspection

Routine inspection of power transformer should be performed every 3-years or whenever the frequency of operation counter of OLTC is over than 10,000 operation.

3.3.2 Inspection method

3.3.2.1 Dry type power transformer

(a) Under normal load, check transformer temperatures with an IR camera.

(b) If the temperature rise (above ambient) is near or above nameplate rating, check for overloading.

(c) Check the temperature alarm for proper operation.

(d) Check enclosures and vaults/rooms for dirt accumulation on transformer surfaces and debris near or against enclosures.

(e) Remove all items near enough to affect air circulation.

(f) To avoid dust clouds, a vacuum should first be used to remove excess dirt. Low pressure (20 to 25 psi) dry compressed air may be used for cleaning after most dirt has been removed by vacuum. The transformer must be de-energized before this procedure unless it is totally enclosed and there are no exposed energized conductors. Portable generators may be used for lighting.

(g) After de-energizing the transformer, remove access panels and inspect windings for dirt- and heat-discolored insulation and structure problems. It is important that dirt


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not be allowed to accumulate on windings because it impedes heat removal and reduces winding life. A vacuum should be used for the initial winding cleaning, followed by compressed air. Care must be taken to ensure the compressed air is dry to avoid blowing moisture into windings. Air pressure should not be greater than 20 to 25 psi to avoid imbedding small particles into insulation.

(h) After cleaning, look for discolored copper and insulation, which indicates overheating. If discoloration is found, check for loose connections.

(i) If there are no loose connections, check the cooling paths very carefully and check for overloading after the transformer has been re-energized.

(j) Look for carbon tracking and cracked, chipped, or loose insulators.

(k) Look for and repair loose clamps, coil spacers, deteriorated barriers, and corroded or loose connections.

(l) Check fans for proper operation including controls, temperature switches, and alarms.

(m) Clean fan blades and filters if needed. A dirty fan blade or filter reduces cooling air flow over the windings and reduces service life. Adding filters is only necessary if the windings are dirty upon inspections.

3.3.2.2 Oil immersed power transformer

(a) Record the history of inspected equipment including surge arresters. (Refer to inspection report)

(b) Perform the routine inspection of external main body and accessories according to inspection checklist. (Refer to inspection report) • Record the status of what should be maintained numerically or take a picture. • Verify the condition of the power cooling fan and OLTC before de-energized. • Check closely whether any evidences of leakage are and report to a supervisor at once if any. • If the upper of power transformer is contaminated due to dirt, perform the water cleaning of it before the external inspection. Note: Parts where the water could be immersed should be protected using a polyvinyl resin.


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Table 2 Details of routine inspection

Item Inspection method Countermeasure

Dielectric strength

measurement

Water content and

acid value measurement Insulating oil

Gas analysis

- comparison with early record

- performing regular inspection

every 3-year

Oil filtration,, de-airing,

special inspection

Insulation resistance measurement - Measurement between windings,

between winding and ground

Respiratory equipment - Discoloration of more than 2/3

of moisture absorbent

- Replacement of

moisture absorbent

Grounding condition

- Earthing of bus duct, tank, LA

- Earthing wire ‘s contact with

case and clothing damage

- Re –tightness

- Rust removal,

- Replacement of

grounding wire

Insulation resistance

And operation

- Noise, vibration

- Measurement using 500V

insulation resistor

(more than 5MΩ)

- Operation for sufficient period

to prevent moisture in summer

season

- Valance adjustment

Ventilator

Bearing - Noise - Replacement


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Item Inspection method Countermeasure

Turpentine - Noise, operation of oil gauge - Replacement

Coating - Rust - Re-coating

- Terminal tightness

- Unnecessary substance

- CT short circuit and connection

- Gasket replacement

- replacement of heater

and thermostat Terminal box and distribution board

- Insulation resistance of

control cable

Nitrogen bottle equipment - Pressure drop (normally use of

6 months)

- Replacement of

nitrogen bottle

Insulating oil - Breakdown voltage, acid value,

moisture content

-Filtration,

replacement

Transfer switch

- Contact status of contact maker

- Discharge marks of contact part

- Tightness of straining part

- Partial replacement

or inspection with

manufacturer

- Operation and terminal tightness

- Noise occurrence

- Moisture infiltration

Tap changer

Moving equipment

- Grease and gear oil

- Partial replacement,

washing, re-spread,

oiling

Terminal tightness, crack,

stain

- Re-tightness,

cleanness Others

Various meter and relay - Replacement


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3.4 Special inspection Special inspection of power transformer is to check the conditions of internal windings, a connection point, and the transaction of insulating oil after opening power transformer’s manhole including routine inspection items. Therefore it is recommended the special inspection should be carried out by manufacturer of the power transformer or a special maintenance company under GECOL’s supervision.


Special inspection of power transformer should be performed according to checklist when something wrong in equipment is discovered or the result of routine inspection is poor.


Inspection items shown below should be conducted according to test procedures including close internal inspection, OLTC diverter S/W inspection, oil filter system inspection, insulating oil changing work. - Measurement of insulation resistance between winding and ground - Measurement of transformer turns ratio - Measurement of short-circuit impedance and load loss - Measurement of dielectric strength of insulating oil (dielectric routine tests) - Test on on-load tap-changers, where appropriate - Operation test of various protective devices - Automatic and manual operation test of cooling equipment

4. Test method

4.1 Oil testing

4.1.1 Insulating oil sampling

Samples can be drawn from energized transformers, although extreme caution should be observed when working wound an energized unit. It is a good practice, for both energized and de-energized units, to attach an auxiliary ground jumper directly from the sample tap to the associated ground grid connection.


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4.1.1.1 Considerations

(a) Glass bottles are excellent sampling containers because glass is inert and they can be readily inspected for cleanliness before sampling. Impurities that are drawn will be visible through the glass. The bottles can be stoppered or have screw caps, but in no instance should rubber stoppers or liners be used; cork or aluminum inserts are recommended. Clean, new rectangular-shaped cans with screw caps and foil inserts are also good, especially when gas-in-oil analysis is to be performed. Glass bottles and cans are well suited if the sample must be shipped or stored. For standard oil testing, a small head space should be left at the top of the container to allow for this expansion and contraction. For dissolved gas in oil, the can should be filled all the way to the top to eliminate the infusion of atmospheric gases into the sample.

(b) Because the usefulness of oil testing depends on the development of trending data, it is important for oil samples to be drawn under similar conditions. The temperature, humidity, and loading of the transformer should be documented for each sample, and any variations should be considered when attempting to develop trending data. Samples should never be drawn in rain or when the relative humidity exceeds 70 percent. Different sampling techniques can alter the results, and steps should be taken to ensure that all samples are drawn properly.

(c) When possible, oil samples should always be drawn from the drain valve at the bottom of the tank. Because water is heavier than oil, it will sink to the bottom and collect around the drain valve. To get a representative sample, at least 1 liter should be drawn off before the actual sample is taken. If a number of samples are taken, they should be numbered by the order in which they were drawn.

4.1.1.2 Methods (a) Wash the test tubes with acetone, dry them and re-wash them with the same

insulating oil. (b) Extract samples from a tested..

※ Material of test tube should not include any jade or lead and a rubber should not be used as the cap of test tube.


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4.1.2 Dielectric breakdown voltage test

The dielectric strength is an indication of the oil’s ability to withstand electrical stress.

(a) After washing the test tube with the extracted insulating oil, keep insulating oil to be tested in it up to a red scale mark slowly in order to prevent a bubble from bringing out. That is, oil level should be over 20mm from the upper portion of an electrode. The electrodes are two discs, exactly 12.5mm in diameter and placed 2.5mm apart.

(b) Place the test tube fixed with bolts on the tester.

(c) The tester must be earthed in order to get rid of residual electric charges. At this time, safety should be paid attention to because very high voltage brings about on it.

(d) Impress AC voltage on it. Raise the voltage at a constant rate, until an arc jumps through the oil between the two electrodes.

(e) The voltage at which the arc occurs is considered the dielectric strength of the oil. But, momentary partial discharge should be not regarded as dielectric breakdown, but only the voltage which makes the breaker of tester cut off should be regard as the dielectric breakdown voltage.

(f) Perform next test after the bubbles which might bring about in the insulating oil disappear by leaving that oil alone for about one minute since a prior test. At this time, this oil sample could be stirred up to the degree that bubble doesn’t bring about so that carbide attached on the surface of the electrode would be eliminated.

(g) When the same oil sample is tested two times, the differentials of test results should not exceed 10kV.

(h) The allowable value of dielectric strength of insulating oil in power transformer is as follows. But the dielectric strength of power transformer GECOL uses should exceed 50kV/2.5mm.


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Table 3 Allowable value of dielectric strength of insulating oil

Description Dielectric breakdown voltage Condition Remark

New oil More than 40kV - -

More than 30kV Good -

Operating oil

Less than 30kV Poor Filtering or replacement

(i) The dielectric breakdown voltage of insulating oil which is used in a diverter

chamber of OLTC GECOL uses should exceed at least 25.

4.1.3 Acid value measurement

When insulating oil contacts with air it would produce an oxidized substance with reaction of oxygen and its acid value would increase. If this acid value exceeds 0.2, the oxidized substance would become sludged. This would have a bad influence upon the function and cooling of transformer.

4.1.3.1 Definition of acid value

The quantity (mg) of KOH that is needed to neutralize total acid component included in 1g of insulating oil.

4.1.3.2 Measurement methods of acid value

(a) After washing a test tube well, extract about 20 ~ 30cc of oil from the bottom drain valve of power transformer.

(b) Put 5cc of the extracted insulating oil into the test tube for measurement. If the temperature of this insulating oil is high, perform this test after sealing and cooling it

down until its temperature reaches 10 ~ 30.

(c) Put the same quantity of indicator (thymolphthalein alcohol or alkaliblue 6B alcohole) into the same test tube. And stir this tube in the proportion of about 130 times per 1 minute and then leave it alone for 2 ~ 3 minutes until insulating oil and


- 23 -GECOL

extracted substance would be divided.

(d) Put the regulated neutralizing liquid into an injector. Then inject it into the test tube in each scale and record the amount of neutralizing liquid from the scale mark of the injection when the color of liquid in the tube turn from blue or blue-green to reddish brown or reddish purple.

(e) Repeat the procedure from another sample. This value acquired from second measurement is the acid value of this insulating oil.

(f) The point of reference of acid value of insulating oil is as follows.

Table 4 Allowable acid value of insulating oil

Acid value Condition Remark

Less than 0.02 New oil -

Below 0.2 Good -

0.2 ~ 0.4 Attention Replacement as soon as possible

More than 0.4 Bad Replacement immediately

Figure 1 Acid value measurement

Extract about 20 – 30cc of oil

Put 5cc of extracted insulating oil

Mix them well

Put the regulated neutralizing liquid

by using injector

The amount of neutralizing liquid is the acid value of the

insulating oil when the color of liquid turn from blue to

reddish purple.

Put 5cc of indicator


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4.1.4 Water content measurement

Water content is very important in determining the serviceability of an oil; the presence of moisture (as little as 25 parts per million (ppm)) will usually result in a lower dielectric strength value. Water content is especially important in transformers with fluctuating loads. As the temperature increases and decreases with the changing load, the transformer’s oil can hold varying amounts of water in solution. Large amounts of water can be held in solution at higher temperatures, and in this state (dissolved) the water has a dramatic effect on the oil’s performance. Water contamination should be avoided.

(a) Water content is expressed in parts per million (ppm), and although water will settle to the bottom of the tank and be visible in the sample, the presence of free water is not an indication of high water content, and it is usually harmless in this state. The dissolved water content is the dangerous factor; it is usually measured by physical or chemical means. A Karl Fischer titrating apparatus is one of the more common methods of measuring the dissolved water content.

(b) Following table 5 lists the acceptable values for the laboratory test results for various insulating oil.

Table 5 Acceptable values for the water content test

Description Amount of water content Remark

66kV

30kV Less than 25 ppm

Follow manufacture’s requirements

prior to test values

4.1.5 Gas analysis

4.1.5.1 Maintenance management through gas analysis from insulating oil

Abnormal phenomenon inside of oil filled equipment accompanies dielectric breakdown and the generation of heat like partial overheating. The materials, which contact with these heating sources, such as insulating oil, insulating paper, pressbord, bakelite are influenced by the heat, and produce hydrogen, carbon monoxide, carbon dioxide, gas of hydrocarbon after their resolution.

Most of these gases are resolved in the insulating oil. Therefore it is possible to assume the abnormality and its degree of the inside of power transformer by examining the amount and


- 25 -GECOL

composition of the gas through abstraction and analysis of them.

The method of gas analysis from insulating oil is the most widely popularized diagnosis technique at present because it enables us to find out even the detailed trouble at early time without stopping the operation of power transformer.

4.1.5.2 Method of gas analysis from insulating oil

(1) Extracting oil

Extract oil through drain valve on the bottom part of power transformer. At this time, this oil should not be contacted with air as possible as it can by being extracted a little with overflow from a closed instrument.

(2) Analysis methods and sorts of analyzed gas

Gas chromatography is mainly used as the method to analyze the extracted gas and it is usually popular to measure the level of gases such as hydrogen, carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene, etc.

(3) Point of reference

Allowable value by gas ingredients is as following table 6.

Table 6 Allowable value by gas ingredients for gas analysis

H2 CO2 C2H4 CO CH4 C2H2 C2H6 Sort

of

Gas Hydrogen Carbon

dioxide Ethylene

Carbon

monoxideMethane Acetylene Ethane

TCG Judgment

400

-

800

Over

700

300

-

750

400

-

700

250

-

750

25

-

80

250

-

750

1000

-

2500

Attention

Below

66kV 801

-

1200

-

751

-

1000

700

-

1000

751

-

1000

81

-

100

751

-

1000

2501

-

4000

Abnormality

NOTE1: If the average value of 3-time analysis of TCG exceeds 300ppm/month its status can be judged

as dangerous.

NOTE2: TCG (Total Combustible Gas) : The total amount of combustible gas, that is, the sum of gas

series of hydrogen, carbon monoxide, hydrocarbon)


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The analysis interval by conditions is following table 7.

Table 7 Interval by conditions for gas analysis

Condition Normality Attention Abnormality Danger

Analysis interval 1 time / 3 years 1 time / 3 months 1 time / month On demand

Countermeasure Regular analysis Monitoring Total investigation Internal inspection

NOTE: Power transformer of which mechanical protective devices are operated must be first analyzed.

4.2 Insulation resistance measurement

4.2.1 Purpose of insulation resistance measurement

Insulation resistance tests (Megger tests) are performed to determine the insulation resistance from individual windings to earth or between individual windings. Knowledge of the insulation resistance is of value when evaluating the condition of the transformer insulation.

4.2.2 General

Insulation resistance is commonly measured in megohms, (MΩ).

It should be stated, that variations in insulation resistance can be caused by numerous factors including: design, temperature, dryness and cleanliness of parts, especially of bushings. When insulation resistance falls below specified value, it can often be brought back to the required value by cleaning and drying.

Insulation resistance varies with the applied voltage. Any measurement comparisons should always be carried out at the same voltage.

IEEE Std C57.12.00 also specifies the insulation resistance measurement between core and earth. It shall be measured after complete assembly of the transformer at a level of at least 0.5 kV DC for 1 minute.

4.2.3 Initial conditions


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(a) Open the transformer’s 1st and 2nd circuit breaker and disconnecting switch

(b) Check whether the transformer is not energized by using detector.

(c) Disconnect the transformer’s neutral point.

4.2.4 Testing procedure

Figure 2 Insulation resistance measurement of power transformer

(1) Measurement of insulation resistance between the winding and the ground

(a) Megohms has an earth terminal (E) and voltage terminal (LINE) like TEST 1. Connect the earth terminal (E) of them with the grounding wire of the transformer.

(b) Connect the voltage terminal (LINE) of a megohms with a terminal of primary winding (P).

(c) After finishing the connection, operate a megohms-meter and measure the insulation resistance between P and E.

(d) Reconnect the voltage terminal (LINE) of megohms with a terminal of the secondary winding (S) and measure the insulation resistance between S and E.

(2) Measurement of insulation resistance between windings

(a) Like following TEST 2, connect one of both terminals (E, LINE) of megohms-meter with the primary winding (P) and connect another with the secondary winding (S)

Transformer Transformer

TEST 1 TEST 2


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(b) Measure the insulation resistance between P and S.

4.2.5 Results

(1) Calculation formula

Minimum allowable value of insulation resistance = 1,000(kVA)outputNominal

(V)voltageNominal+

(2) Minimum safety insulation resistance value

The minimum limit of safety insulation resistance of power transformer should be referred the below table 8.

Table 8 Minimum safety insulation resistance value

Oil temperature (ºC)

Nominal voltage 20 30 40 50 60

More than 66kV 1200 600 300 150 75

30kV 1000 500 250 125 65

11kV 800 400 200 100 50

4.2.6 Considerations when using megohm-meter

(a) Measurer should read the instruction manual and be well aware of usage method. In case of battery type megohm-meter, check whether batteries in it are available or not.

(b) In case of equipment over 1,000V 2,000MΩ Megohm-meter should be used for the insulation resistance measurement. On the other hand, Equipment over 1,000V should be measured with 500V 1,000 MΩ Megohm-meter.

(c) A lead of megohms should be as possible as shorten and its wire should have good insulation to the grounding.

(d) Before using the megohm-meter, measurer should check whether it indicates 0 when the both terminals of lead are short-circuited or whether it indicates ∞ when opened.

(e) Measurer should check whether the terminals of transformer to be measured are charged and disconnect any lead and lightening, etc connected with the transformer.

(f) Error factor of insulation resistance measurement caused by leakage current should be removed by cleaning the wall tube insulator of bushing. If possible there is any


- 29 -GECOL

error, guard-ring could be used to reduce an error.

(g) In case of transformer with large capacity, there is a possibility that the megohm-meter first indicates 0 due to the charging current. But in this case after some time passed out, it indicates correct value, unlike short-circuit.

(h) As the insulation resistance is influenced by the temperature of object measured, in case of transformer this measurement should be carried out at least more than 3 times, that is when the oil temperature in transformer is, directly after interruption for the measurement, the highest, when it is a little down, and when it is similar to its circumstance’s one. In additional a measurer should record the circumstance temperature, the degree of moisture and whether in measurement so that the condition of insulator could be got hold through the comparison with previously measured value.

(i) A measurer should read the average of measured values when the indicator vibrates due to the induced voltage inside of circuit in measurement. But in case of measurement at the place like a substation where the induced voltage brings about so much, a generator type megohm-meter would be better to use.

4.3 Test on on-load tap-changer

4.3.1 Operation test

With the tap-changer fully assembled on the transformer, the following sequence of operations shall be performed without failure:

(a) With the transformer un-energized, eight complete cycles of operation (a cycle of operation goes from one end of the tapping range to the other, and back again).

(b) With the transformer un-energized, and with the auxiliary voltage reduced to 85 % of its rated value, one complete cycle of operation.

(c) With the transformer energized at rated voltage and frequency at no load, one complete cycle of operation.


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Power Transformer Routine Inspection Report Work name:

S/S & equipment name:

Inspection date: 200 . . . Weather & Temperature:

Foreman: Supervisor:

1. Specification Serial number Year of manufacture

Phase 3 Ф Connection

Capacity

Voltage

Power transformer

Plant of manufacture

Series number Year of manufacture

Type

Operating number OLTC

filter Plant of manufacture

2. Routine inspection 2.1 Details of Inspection

Inspection

item Details of inspection standard result

Content of badness &

maintenance

Correspondence of moving equipment and OLTC Tap number

Oil and its leakage in gear box

Grease of gear, shaft, bearing

Relaxation of each bolt & nut, pin

Spring transformation and rust

OLTC

Moving

Equipment

Moisture proof and door packing

Motor operation of pump

Cleanness of filter

Joint of source terminal

Thermostat, pressure gauge, timer

Oil leakage, rust of pipe and valve

OLTC

Filter

Equipment

Ventilation after inspection (work after 30 minutes

since filter operation)


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Operation and damage of fan motor

Operation and damage of oil pump

Leakage and rust of oil pump

Operation of oil flow indicator

Fan Motor

&

Oil Pump

Corrosion of connected cable

Leakage and transformation Tank case

Rust and coating

Leakage, explosion, transformation

Coating and rust

Vibration in motor’s operation

Heatproof

Equipment

Opening and closing of valve

Damage of insulator Bushing

Cleanness and oil leakage

Oil leakage and rust of pipe Conservator

Slope angle of pipe

Operation of winding thermometer

Operation of oil thermometer Thermometer

Resistance value of thermostat

Cleanness of the inside of panel

Rust of terminal block

N.F.B and Magnetic S/W

Relay and transfer S/W

Joint of terminal block

Local Panel

Moisture proof and door packing

Operation of impact pressure relay

Operation of leased safety equipment

1st, 2nd operation of B.H relay

Operation of main body and OLTC oil gauge

Mechanical

Protective

Equipment

Operation of OLTC protective relay

Operation of oil gauge and nitrogen pressure gauge Oil

preservation

equipment Silicagel breather including OLTC

Oil leakage B.C.T

terminal

board Relaxation of nuts of B.C.T terminal


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Tightness of terminal of main circuit Others

Insulating resistance of control panel (500V 1000MΩ)

2.2 Test of Routine Inspection

- Insulating resistance measurement (instrument: 1,000V 2,000MΩ)

(Unit: MΩ)

Description HV-E LV-E HV-LV

H1-E H2-E H3-E X1-E X2-E X3-E H1-L1 H2-L2 H3-L3 30kV

66kV

- Dielectric breakdown voltage test of insulating oil

(Unit: kV)

Times

description 2 3 4 5 7 8 9 10 Average

Before

filtering

After

filtering

※ Average value should be yielded by means of following method

1) Extract 2 samples of insulating oil, and measure each of them 5 times respectively.

2) Sum the rest, 8 values, excluding first one of measured values of each sample and finally average the sum.


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2.3 Opinion on the Inspection Result

Exterior

Interior

Others


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Insulation resistance (MΩ

)

More than 66kV

22kV - 66kV

22kV - 66kV Bad

Good

Oil Temperature of Transformer (ºC)


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II. Gas Insulated Switchgear (GIS)


- 36 -GECOL

1. General

1.1 Description GIS (Gas insulated switchgear) is a total switchgear which includes bus, switchgear, instrument transformer, surge arrester inside of it and is sealed up with SF6 gas which has very good characteristics of insulation and arc-suppression.

1.2 Structure (Cubicle type GIS)

1. View ports

2. Three-position switch operating

Mechanism with auxiliary contacts

3. Three-point switch

4. Pressure sensor

(Temperature-compensated)

5. Circuit-breaker operation mechanism

6. Three-position switch between

Cable and circuit-breaker

7. Grounding switch operating

mechanism with auxiliary

contacts

8. Grounding switch cable side

9. Cable socket

10. Cable plug

11. Main earth bar

12. Voltage resistant cover

13. Measuring sockets for capacitive

voltage indicator system

14. Multifunctional socket for

testing, potential transformer

15. Current transformer

16. Pressure relief disc

17. Circuit-breaker

18. Pressure relief duct

19. Busbar

Insulating Gas


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1.3 Rating

Rated voltage

(kV)

Rated short time withstand

current(kA)

Rated peak withstand

current (kApeak)Rated nominal current (A)

36 31.5 79 1,250 1,600 2,000 2,500 3,150

2. Delivery and storage The switchgear cubicle is supplied covered in plastic and strapped vertically to a pallet. All equipment, for example, the operating mechanisms and the bay computer are assembled in the cubicle on delivery. The switching devices are locked in the disconnected position during transport for reasons of safety. Use a fork lift truck when unloading. There are no lifting eyes, but lifting beams can be fitted to the cubicle’s ends if the plastic sheet is opened. Alternatively, lifting straps can be used if these are placed under the bottom of the pallet so that the pallet bears all the weight of the cubicle when lifting.

When unloading inspect for signs of transport damage. Also check the number of packages against the delivery note and order documents. Allow the packaging to remain in place as long as possible. If the switchgear is to be stored before installation the following applies:

(a) The switchgear may be stored outdoors under a rain cover/roof with undamaged/unopened transport packaging for a maximum of 3 days.

(b) Storage shall take place in a tempered (warmer than 15 °C) and dry indoor building when storing for longer than 3 days.

(c) When storing equipment packed for export in plywood or wooden crates this should be done under a rain cover/roof. Storage can then be done for a maximum of 12 weeks.

(d) A tempered and dry indoor building (warmer than 15 °C) is recommended for storage periods greater than 12 weeks.

3. Inspection In GIS equipment, inspection works to Gas Circuit Breaker shall be basic because it is the key component and more heavy duties than any other component mechanically and


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electrically.

Therefore it is important to follow the procedures about Gas Circuit Breaker including SF6 gas, and the description about it is detailed mainly.

Concerning about the components except Gas Circuit Breaker, it is recommended that they are inspected at the same inspection period as Gas Circuit Breaker, however so detailed procedure as Gas Circuit Breaker are not described because they are basically maintenance-free components, and the required procedure for them are almost same as what will be described in Gas Circuit Breaker.

3.1 Field inspection before operation Use a check list during the installation inspection. The check list can also be used as verification for the completed installation work. When the installation is complete the following supplementary work and inspection should be carried out:

(a) Check that all assembly work complies with applicable drawings and connection diagrams.

(b) Check that the power cables are anchored, i.e. secured in the cable brackets.

(c) Check, with parallel power cables with outer cone connectors, that cable number two is strain relieved by the cable strain relief.

(d) Check insulation to earth using an insulation tester (megger).

(e) Check the cubicle and unit marking and supplement with signs if necessary.

(f) Check that tools, cable residue, insulation material or other foreign objects are not left in the switchgear, operating areas and in the switchgear room.

(g) Vacuum clean and dust if necessary.

(h) Check that the top plates are fitted on all cubicles.

(i) Shut the operating enclosure’s doors and covers.

(j) Check that the end-plates on the switchgear’s outer ends are fitted and that the nuts are tightened.

(k) Check that the end-plates on the lower frame’s outer ends are fitted.

(l) Check that the fronts are fitted on the lower frames.


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3.2 Daily inspection Daily inspection should be taken in order to check to fault or not at the operating condition device. At this time, important checking point is gas pressure.


Daily inspection should be inspected at the same period of patrol time.


(1) Gas pressure

Read pressure on gas pressure gauge and record the gas pressure, ambient temperature. If any SF6 gas leakage is detected, supply the SF6 gas according to the procedure described in each manual before the gas pressure drops to the alarm pressure. After supplying SF6 gas, close the gas supplying stop valve and then accurately install the protection cover.

(2) Operation counter

Check and record the number of operation.

(3) Space heater

When humidity is high, the temperature drops sharply or the ambient temperature is low, turn on the heater in the control cubicle.

(4) Closing spring

Check that charged/ discharged indicator shows charged.

(5) Others

Check for sign of the abnormal noise.

3.3 Routine inspection


Inspection should be performed every 3-year after start of service or when the frequency of operation counter of the GIS in the control panel is over than 500 operation.


- 40 -GECOL


Conduct maintenance and inspection by utilizing service interruption without discharging SF6 gas.

Conduct a routine inspection at the stoppage of electric current without discharging gas.

Be careful with the following items during this inspection.

NOTE 1: Turn off the power source of control circuit in the local control cubicle.

NOTE 2: Before routine inspection, closing spring must be released and tripping spring must be released.

(1) Gas tank

- Check bolts and nuts of flange and cover connection for looseness.

- Check the surface condition of tank, whether rusty or not.

(2) Gas system

- Check bolts and nuts of gas pipe and gas density detector, etc.

- Check gas pressure on gas pressure gauge.

- Gas leak test should be carried out on gas system, if necessary.

(3) Control mechanism assembly

(a) Oil dashpot

- Check the oil level.

(b) Operating rod

- Check nuts and lock plates for looseness.

- Check split pins and joint pins.

(4) Operating mechanism assembly

(a) Auxiliary switch

- Check positive contact and also check each part for normal tightening.

- Contact touching condition should be checked from the terminals of the terminal board.

(b) Link mechanism

- Check the surface condition of pins, hooks etc.


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- Apply designated grease according to the guide of exchanging parts and maintenance.

(5) Wiring and others

- Check terminals for looseness. Tighten terminals.

- Check box interior. Clean up box interior

- Check rusty parts. Paint rusty parts

(6) Operation test

Manual operation should be performed in accordance with operation test manual.

(a) Closing spring can be charged by manual handle.

(b) During charging stage, operation counter shows one added number. And indicator shows "OPEN" name plate.

(c) After charging closing spring pushing the close button after remove manual handle, indicator shows "CLOSE" name plate.

(7) Opening system

- Check the stroke of operating link.

- Confirm that the stroke keeps the space of operating link first manufactured.

(8) Insulation resistance check

(a) Insulation resistance check of main circuit.

(b) Insulation resistance check of control circuit.

3.4 Special inspection It is recommended special inspection of GIS should be performed by manufacturer or special maintenance company under supervision of GECOL engineer.


Inspection should be performed every 6-year after start of service or when the frequency of operation counter of the GIS in the control panel is over than 2,000 operation.



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Conduct maintenance and inspection discharging SF6 gas.

(1) Stationary arcing contact

- When contact surface is found uneven, remove it from interrupter, and contact it with sandpaper.

- When the amount of wear has become value designated on the GIS manual or over, replace the contact with a new one. Apply thin coat of designated grease to the contacts.

(2) Moving arcing contact

- When surface is found uneven, polish the surface with a smooth cut file.

- When the amount of wear has become value designated on the GIS manual or over, replace the contact with a new one.

- Apply thin coat of designated grease to the contacts.

(3) Insulation nozzle and Insulation cover

- Use lint free cloth to clean up the interior and exterior. When the nozzle's or cover's inner diameter is enlarged by value manufacture ensures or more, replace it with a new one.

(4) Absorbent

- Replace with a new one. Exchange it quickly just before vacuum drying.

(5) Insulation material

- Use lint free cloth to clean up the surface.

(6) Oil dashpot

- Remove the oil plug and oil. Then fill with new oil to the position of oil plug. When oil leaks are found, disassemble and check the oil dashpot. (Oil : Transformer oil )

(7) Control mechanism

- Check pin, links, levers, operating rod and split pins.

- Check nuts and lock plates for possible looseness. Apply designated grease to pins.

(8) Closing hook (Tripping hook)

- Clean up and apply a small amount of Lithium base grease to the hook, pins and rollers.

- Check the state of hook engagement under both closed and open position. In case of link mechanism clean up and apply a small amount of the links, pins, and rollers.


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(9) Auxiliary switch

- Check contacts.

- Check terminal for tightening. Apply a thin coat of grease to the linking pin.

- Re-tighten terminal and bolts.

(10) Pressure gauge

- Clean up and calibrate the pressure gauge.

- Be careful not to allow ingress of dust into pressure gauge mounting hole pressure gauge as been disconnected.


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Gas Insulated Switchgear (GIS) Inspection Report Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site GIS ID

Rated Voltage Rated Load Current

Plant of Manufacture Serial Number Year of Manufacture

Item Inspection result Remark

1. Gas tank condition

2. Gas system

3. Interlocking system

4. Control mechanism assembly

5. Operating mechanism assembly

6. Terminals, box interior, rusty part

7. CB operation test

8. Opening system

9. Insulation condition, clean if needed.

10. CT & VT condition, clean if needed

11. Insulating resistance measurement

12. Fitting condition of enclosure

Inspection

Before

Operation ,

Routine

Inspection

13. Clean and dust condition of surrounding

1. Voltage (kV)

2. Load current (A) General item

3. Operation frequency (times)

Remark

Foreman: Date: Sign:

Office / Section supervisor : Date : Sign:


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III. Circuit Breakers


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1. General

1.1 Description Circuit breakers are a special form of switching mechanism, which can open and close circuits under both normal and abnormal conditions. When they are electrically controlled, they can be operated locally or remotely, or by both modes. Oil, SF6 gas, vacuum, and air are the insulating mediums used on most installations. The selection of the insulation generally relates to the voltage level being interrupted.

1.2 Types of medium voltage circuit breaker

1.2.1 Oil insulated circuit breaker

In the past, oil break device has predominated, but now several alternative methods of arc interruption are used in distribution voltage circuit breakers.

Early oil designs featured plain-break contacts in a tank of oil capable of withstanding the considerable pressure built up from large quantities of gas generated by long arcs. After the lapse of time, various designs of arc control device were introduced to improve performance. These were designed such that the arc created between the contacts produces enough to break down the oil molecules, generating gases and vapors which by the cooling and de-ionizing of the arc resulted in successful clearance at current zero. During interruption, the arc control device encloses the contacts; the arc is lengthened and cooled. The use of oil circuit breaker is reducing significantly in most areas of the world because of the need for regular maintenance and the risk of fire in the event of failure.

1.2.2 SF6 Gas insulated circuit breaker

Sulphur hexafluoride (SF6) is the most effective gas for the provision of insulation and arc interruption. A SF6 gas insulated circuit breaker includes a closed tank filled with an insulation gas, one pair of separable contacts disposed in the closed tank, a supporting frame supporting the closed tank, an opening spring for performing an opening operation of the pair of contacts, a closing spring for performing a closing operation of the pair of contacts, and an actuating mechanism box accommodating an opening coil which is adapted to receive a circuit opening command for the contacts, a closing coil which is adapted to


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receive a circuit closing command for the contacts and an actuating mechanism for rendering the opening spring and the closing spring operative in response to an activation of the opening coil and the closing coil. A first spring casing accommodates the opening spring and is secured on the closed tank, and a second spring casing accommodates the closing spring and is secured on the supporting frame.

Figure 3 SF6 gas insulated medium voltage

circuit breaker (Model HD4/R by ABB)

1. Protection relay (on request)

2. SF6 pressure signalling device (on request)

3. Nameplate

4. Shaft for manual closing spring charging

5. Closing push button

6. Reset of protection circuit-breaker of geared

motor (on request)

7. Current sensors for circuit (on request)

8. Mechanical signalling device for circuit breaker

open/closed

9. Opening push button

10. Key lock (on request)

11. Mechanical signalling device for closing springs

charged/discharged

1.2.3 Vacuum circuit breaker

The vacuum interrupter is a simple device, comprising only a fixed and a moving contact located in a vacuum vessel.

The principle of operation of a vacuum interrupter is that the arc is not supported by an ionized gas, but is a metallic vapor caused by vaporization of some of the contact metal. At zero current, the collapse of ionization and vapor condensation is very fast, and the extremely high rate of recovery of dielectric strength in the vacuum ensures a very effective


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interrupting performance. The features of a vacuum interrupter which are key to its performance are the contact material, the contact geometry and ensuring that the envelope (a glass or ceramic tube with welded steel ends) remains vacuum-tight throughout a working life in excess of 20 years. A typical vacuum interrupter is shown in figure 4.

The circuit breaker is located within a switchgear housing. The main insulation in the housing is usually air, although some designs now have totally sealed unit a filled with SF6. Structural isolation is required to support current-carrying conductors; this is normally some type of cast resin. Thermoplastic materials which can be injection-molded are often used for smaller components, but larger items such as bushings which are insulation-covered are usually made from thermosetting materials such as polyurethane or epoxy resin mixed with filler to improve its mechanical and dielectric properties.

Figure 4 Typical vacuum circuit breaker

Moving contact

Ceramic body

Stainless

Steel end

Stainless Steel

bellows Sputter shield

Fixed contact

Stainless

steel end


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1.3 Rating

Rated

voltage

(kV)

Rated short-circuit

breaking current

(kA)*

Rated short-circuit

making current

(kApeak)

Rated normal current (A)**

12.5 31.5 630 800 1250

16 40 630 800 1250

25 62.5 630 800 1250 2000 2500

31.5*** 79 1250 1600 2500 3150 4000

12

40 100 1250 1600 2500 3150 4000

12.5 31.5 630 800 1250

16 40 630 800 1250 1600

25 62.5 630 800 1250 2000 2500

31.5*** 79 1250 1600 2500 3150 4000

36

40 100 1250 1600 2500 3150 4000

12.5 31.5 800 1250

16 40 800 1250

25 62.5 1250 1600 2000 2500 3150

31.5*** 79 1250 1600 2500 3150 4000

72.5

40 100 1600 2000 2500 3150 4000

*, ** : These values shall be determined by GECOL. *** : These are preferred values.

1.4 Consideration for safety practices Before initiating any maintenance inspection which requires touching a circuit breaker, check to ensure that:

(a) The circuit breaker has been tripped (open).

(b) The circuit breaker is disconnected from the circuit on both sides, either by opening disconnect switches or by removing the drawout portion of the circuit breaker from the switchgear dependent upon the installation.

(c) All control circuits are open and potential transformer fuses are removed.

(d) The supply to pneumatically and hydraulically operated circuit breakers is shut off.


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(e) Wound springs in stored-energy mechanisms have been released.

(f) Circuit breakers and controls are properly tagged.

(g) After the circuit breaker has been disconnected from the electrical power, attach the grounding leads properly before touching any of the circuit breaker parts.

(h) Suitable barriers are installed between the circuit breaker and adjacent apparatus that may be energized. In crowded installations, barriers may be of rope or net, with suitable danger flags, or of temporary rigid construction using insulating material.

(i) Requirements of departmental safety practice are being observed.

(j) Do not lay tools down on the equipment while working on it as they may be forgotten when the equipment is placed back in service.


2.1 Delivery The switchboard sections are usually fixed to wooden pallets. Delivery shall be carried out by means of a fork-lift truck or a mobile crane with hoisting tackle. Choose the transportation equipment according to the unit’s weight and center of gravity provided on the packaging and in the accompanying documents.

Be careful not to damage the plastic sheeting since it protects the unit against weather and dirt.

When handling circuit breaker by means of crane hook the lifting bolts to the relevant support. While handling pay the utmost attention not to put any stress on the insulating parts and on the circuit breaker terminals. Before putting into service, remove all the lifting eyebolts. But, handling by means of fork-lift truck can be carried out only after the circuit breaker has been positioned on a sturdy support.


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Figure 5 Faulty delivery of circuit breaker

2.2 Storage When a period of storage is foreseen, ask manufacturer to provide suitable packing for the specified storage conditions. On receipt the apparatus must be carefully unpacked and checked as described in checking on receipt. If immediate installation is not possible, the packing must be replaced, using the original material supplied. Insert hygroscopic substances inside the packing, with at least one standard bag per piece of apparatus. Shall the original packing not be available and immediate installation is not possible, store in covered, well-ventilated, dry, dust-free, non-corrosive ambient, away from any flammable materials and at a proper temperature between –5 °C and +45 °C. In any case, avoid any accidental impacts or positioning which stresses the structure of the apparatus.

3. Inspection

3.1 Medium voltage circuit breakers

3.1.1 Daily inspection

Daily inspection of circuit breaker shall be performed during patrol, making a visual external inspection, looking for oil leaks, loose mechanism parts, oil level, bushing condition, indicating lights, and any other malfunction.


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3.1.2 Routine inspection

3.1.2.1 Interval of inspection

Routine inspection of medium voltage circuit breaker shall be performed every 3-year or after every 2,000 operations, whichever comes first.

3.1.2.2 Inspection method

(1) Oil circuit breakers

The following suggestions are for use in conjunction with the manufacturer's instruction books for the maintenance of medium-voltage oil circuit breakers:

(a) Check the condition, alignment, and adjustment of the contacts.

(b) Thoroughly clean the tank and other parts which have been in contact with the oil.

(c) Test the dielectric strength of the oil and filter or replace the oil if the dielectric strength is less than 30 kV. The oil shall be filtered or replaced whenever a visual inspection shows an excessive amount of carbon, even if the dielectric strength is satisfactory.

(d) Check breaker and operating mechanisms for loose hardware and missing or broken cotter pins, retaining rings, etc.

(e) Adjust breaker as indicated in instruction book.

(f) Clean and lubricate operating mechanism.

(g) Before replacing the tank, check to see there is no friction or binding that would hinder the breaker's operation. Also check the electrical operation. Avoid operating the breaker any more than necessary without oil in the tank as it is designed to operate in oil and mechanical damage can result from excessive operation without it.

(h) When replacing the tank and refilling it with oil, be sure the gaskets are undamaged and all nuts and valves are tightened properly to prevent leakage.

(i) Perform an insulation resistance test.

(j) Perform a speed (timing) test.

(k) Check operation of the operation counter.


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(l) Perform a contact resistance test, if necessary for more detailed inspection.

(2) Vacuum circuit breakers

Direct inspection of the primary contacts is not possible as they are enclosed in vacuum containers. The operating mechanisms are similar to the breakers discussed earlier and may be maintained in the same manner. The following two maintenance checks are suggested for the primary contacts:

(a) Measuring the change in external shaft position after a period of use can indicate extent of contact erosion. Consult the manufacturer's instruction book.

(b) Condition of the vacuum can be checked by a hi-pot test if necessary for more detailed inspection. Consult the manufacturer's instruction book.

(3) SF6 gas circuit breakers

(a) Perform an inspection according to the circuit breaker test and maintenance form. Complete all items listed on the form.

(b) Inspect the mechanism.

(c) Check SF6 gas pressure and density monitor contact surfaces.

(d) If possible, cycle the mechanism electrically. Check:

- Close function

- Trip function

- Reclose function

- Trip free function

(e) Service and inspect the hydraulic system, if any.

(f) Check accumulator or pre-charge pressure.

(g) Check pressure switches.

(h) Service the hydraulic switches, if any.

(i) Measure close and trip coil resistance.

(j) Check stored operations to lockout.


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3.2 Low voltage circuit breakers


Low voltage circuit breakers operating at 600 volts alternating current and below shall be inspected in the process of patrol and at the same time of the apparatus they are attached, depending on their service and operating conditions. And additionally they shall be inspected and maintained if necessary whenever it has interrupted current at or near its rated capacity.


Manufacturer's instructions for each circuit breaker shall be carefully read and followed. The following are general procedures that shall be followed in the maintenance of low-voltage air circuit breakers:

(a) An initial check of the breaker shall be made in the TEST position prior to withdrawing it from to enclosure.

(b) Insulating parts, including bushings, shall be wiped clean of dust and smoke.

(c) The alignment and condition of them movable and stationary contacts shall be checked and adjusted according to the manufacturer's instruction book.

(d) Check arc chutes and replaces any damaged parts.

(e) Inspect breaker operating mechanism for loose hardware and missing or broken cotter pins, etc. Examine cam, latch, and roller surfaces for damage or wear.

(f) Clean and re-lubricate operating mechanism with a light machine oil for pins and bearings and with a non-hardening grease for the wearing surfaces of cams, rollers, etc.

(g) Set breaker operating mechanism adjustments as described in the manufacturer's instruction book. If these adjustments cannot be made within the specified tolerances, it may indicate excessive wear and the need for a complete overhaul.

(h) Replace contacts if badly worn or burned and check control device for freedom of operation.

(i) Inspect wiring connections for tightness.

(j) Check after servicing circuit breaker to verify the contacts move to the fully opened and fully closed positions, that there is an absence of friction or binding, and that


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electrical operation is functional.

4. Test methods

4.1 Contact resistance test

4.1.1 Test method

Before performing the test, make sure the power circuit breaker is de-energized and proper clearance is obtained. Take resistance readings from bushing-to-bushing with circuit breaker closed. Consult the owner’s manual for manufacturer’s recommendations. Readings higher than those listed shall be compared to previous tests and investigated.

Table 9 Example of contact resistance values

Air/Gas/Vacuum Circuit Breakers Oil Circuit Breakers

kV Amperes Microhms kV Amperes Microhms

5-15 600 100 7.2-15 600 300

1200 50 1200 150

2000 50 2000 75

4000 40

23-24 All 500

46 All 700

69 600 500

1200 500

2000 100

115-230 All 800

4.2 DC Hi-pot test for vacuum bottles

4.2.1 X-radiation and electrical charge-built-up


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(a) High voltage applied across open gaps in a vacuum can produce X-radiation. Prolonged exposure to X-radiation at close range can constitute a health hazard unless the source is adequately shielded. In the normal current-carrying mode, no X-radiation is emitted because there are no open contacts. When the contacts are open in service with the specified contact gap at rated voltage (or at 35kV ac or dc for 15.5kV breakers), X-radiation at one meter is below the level of concern. A measure of X-radiation control is provided by the metal shield in the vacuum interrupter and by the metal enclosure of the breaker.

(b) During any Hi-Potting operation and in service at normal operating voltage. The main shield inside the interrupter can acquire an electrical charge that is usually retained after the voltage is removed. This shield is attached to the mid-band ring of the insulating envelop. Always use a ground attached to a hotstick to discharge the ring before touching the interrupter. The discharging operation must connect the mid-band ring to both ends of the interrupter in turn or simultaneously.

(c) When performing DC Hi-Pot test on a substation breaker, place a barrier board between the disconnect support and disconnect to prevent contact with the high voltage during test lead installation.

(d) Always ground the test set before plugging in the power supply.

(e) Unplug the power supply before disconnecting the case ground.

(f) Set the RAISE VOLTAGE control to zero immediately upon completion of the test, and keep the control on zero when not in use.

(g) Remove the ISOLATION PLUS on the Hi-Pot tester before changing lead configuration from open to close breaker test.

4.2.2 Preparing the breaker for testing

Follow these steps to prepare the breaker for testing.

(a) Remove the high voltage compartment covers.

(b) Discharge the interrupter mid-band ring. This is done by touching the interrupter mid-band ring with a ground attached to a hotstick while the breaker is in the closed position and interrupter contacts are at ground potential.

(c) Using a clean dry soft cloth with solvent, wipe off the interrupter insulating envelop and the porcelain bushings to remove any surface contamination acquired during


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shipping, storage, or service.

(d) Verify the contact stroke is properly adjusted according to the manufacturer’s specification.

Caution: Do not energize or Hi-Pot the breaker if the contact stroke is less than the minimum specified.

(e) Replace the high voltage compartment covers.

4.2.3 Test voltage requirements

Each of the different size of interrupters must have the correct test voltage applied. Table 10 shows the voltage ratings and test voltage requirements.

Table 10 Voltage ratings and test requirements

Nominal Voltage Rating of Interrupter

(kV)

Max. Test Voltage DC

(kV)

Max. Test Voltage AC

(kV)

12 18.5 25

36 52.1 73

4.2.4 Test method

The vacuum bottle DC Hi-Pot procedure uses two tests, open bottle, and closed.

Figure 6 shows Hi-Pot tester which is used to provide the stimulus for the test and measurement of the results.


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Figure 6 Example of Hi-Pot tester (Model: Hipotronics 880PL)

4.2.5.1 Open breaker, vacuum bottle integrity

(1) Procedures

Perform the following steps to test the breaker in the open position.

CAUTION: Be sure the RAISE VOLTAGE control is set to zero and the interlocking plug is removed before connecting the test leads.

(a) Connect the Hi-Pot voltage source to one bushing of the pole to be tested and the ground (return) lead to the other bushing. This tests the integrity of the vacuum bottle.

CAUTION: Personnel shall be at least one meter from the breaker suring the test.

(b) Select the correct test voltage using table 10.

(c) Apply the test voltage for one minute. Record the valve measured on the data test sheet.

(d) Turn off the Hi-Pot tester.

(e) Verify the Hi-Pot voltage light is off.

(f) Turn off the AC power.

(g) Remove the interlock plug.

(h) Discharge the center ring of the vacuum bottle.

(i) Remove the return lead and connect it to ground.

(2) Results


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Test results are “GO” or “NO-GO” in nature. Bad-order equipment has a significant amount of leakage current, which trips out the Hi-Pot test set, indicating the bottle has failed the test. Use the Hi-Pot test results (Pass/Fail) in conjunction with the doctor reading and the manufacturer’s dimensional integrity (contact wear measurements) of the bottle to determine whether a bottle shall be replaced.

No attempt shall be made to compare the condition of one vacuum interrupter with another, nor to correlate the condition of any interrupter to low or high values of DC leakage current. There is no correlation.

4.2.5.2 Closed breaker, bushing insulation

(1) Procedures

Perform the following steps to test the breaker in the closed position.

CAUTION: Be sure the RAISE VOLTAGE control is set to zero and the interlocking plug is removed before connecting the test leads.

(a) Connect the Hi-Pot voltage source of the bushing of the pole to be tested and the ground (return) lead to the breaker case. This tests the total pole insulation.

CAUTION: Personnel shall be at least one meter from the breaker suring the test.

(b) Apply the test voltage for one minute. Record the valve measured on the data test sheet.

(c) Using a ground attached to a hotstick, discharge the interrupter.

(2) Results

Test results are “GO” or “NO-GO” in nature. Bad-order equipment has a significant amount of leakage current, which trips out the Hi-Pot test set, indicating that a line-to-ground failure has occurred. Use the Hi-Pot test results (Pass/Fail) to determine whether an interrupter support insulator, bushing, or other component shall be replaced.

No attempt shall be made to compare the condition of one vacuum interrupter with another, nor to correlate the condition of any pole to low or high values of DC leakage current. There is no correlation.


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Circuit Breaker Routine Inspection Report Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site GIS ID



Routine inspection item Inspection result Remark

1. Oil level & leakage

2. Condition, alignment, adjustment of contact

3. Cleaning the tank and parts contacted with the oil

4. Dielectric strength test of oil Basis value: 30kV

5. Insulation resistance test

Oil

6. Contact resistance test

1. Change in external shaft position Vacuum

2. Hi-pot test

SF6 Gas 1. Contact resistance test

1. Mechanical interlocking system

2. Breaker and operating mechanism assembly

3. CB operation timing test

4. CB operation test

5. Cleaning CB Insulator

6. Operation counter

7. Voltage (kV)

General item

8. Load current (A)

Remark




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IV. Disconnecting Switches


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1. General

1.1 Description Disconnecting switch is a mechanical switching device used for changing the connections in a circuit, or for isolating a circuit or equipment from the source of power.

It has no interrupting rating and is intended to be operated only after the circuit has been opened by some other means, such as by a circuit breaker or variable transformer.

1.2 Rating

Rated

voltage

(kV)

Rated short-circuit

breaking current

(kA)*

Rated short-circuit

making current

(kApeak)

Rated normal current (A)**

12.5 31.5 800 1250

16 40 800 1250

25 62.5 1250 1600 2000 2500 3150

31.5*** 79 1250 1600 2500 3150 4000

72.5

40 100 1600 2000 2500 3150 4000

*, ** These values shall be determined by GECOL.

1.3 Consideration

1.3.1 When being installed

1.3.1.1 Personnel safety during installation

Follow the guideline for safety work, as well as manufacturer instructions, user practices. Safety precautions shall be carefully followed.


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1.3.1.2 Instructions for assembly

For satisfactory service, equipment drawings and manufacturer's instructions for switch assembly shall be carefully followed.

1.3.1.3 Alignment

Switches shall be carefully aligned on the supporting structure. Most switches require that the surface on which the bases are mounted shall be flat and true; otherwise, the bases may become twisted when bolted to the structure. Such twisting could cause the switch to be difficult to operate, cause operating parts to be out of alignment, and cause undue strain on the insulator stacks.

1.3.1.4 Rigidity

All switch bases and associated stationary parts shall be rigidly bolted in place.

1.3.1.5 Line conductors

Conductors bolted to the switch terminals shall not subject the switching equipment to undue mechanical forces that could cause contact misalignment.

1.3.1.6 Bus conductors

Bus conductors are acted upon by mechanical forces due to dimensional changes with temperature and by electromagnetic forces. Bus conductors shall be so supported and connected to the switches that these forces will not impair the electrical or mechanical function of the switches.

1.3.1.7 Equipment connections

Contact surfaces shall be clean and smooth. Excess mechanical forces shall be carried by auxiliary supports. When dissimilar metals are combined in a current-carrying joint, adequate protection against galvanic and chemical action shall be provided. Bolted connections shall be adequately torqued as recommended by the switch manufacturer.

1.3.1.8 Ground connections


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The bases and operating handles of substation switches shall be grounded in accordance with the safety guideline. The bases and operating handles of some distribution switches are not grounded. These installations shall follow well-established user practice. The user shall be aware that the grounded base may have been used to establish a predetermined relationship between the phase-to-ground and open-gap withstand voltage values.

1.3.1.9 Adjustments

When the equipment is in place, adjustment shall be made with normal weight or strain on the insulators and current carrying parts.

1.3.2 When being operated

High-voltage disconnecting switches are given no interrupting rating. Low levels of current may be interrupted per the guidelines given in table below.

Table 11 Suggested Guide for interrupting with Vertical-Break Air Switches

Equipped with Arcing Horns and Mounted in Horizontal-Upright Position (Based on

Minimum Phase Clearance to Grounded Objects, Calculated Arc Reach, and

Maximum Operating Voltage)

Rated Maximum

Voltage L-L

(kV)

Rated Withstand

Voltage Impulse

(kV)

Resistive or Transformer

Excitation Current

(Amps)

Bus, Line, or Cable

Capacitive Current

(Amps)

12 110 3.1 1.1

36 200 2.8 1.0

72.5 350 2.2 0.8


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Table 12 Suggested Guide for interrupting with Vertical-Break Air Switches

Equipped with Arcing Horns and Mounted in Horizontal-Upright Position (Based on

Horn-Gap Switch-Phase Spacing (Centerline to Centerline), Calculated Arc Reach,

and Maximum Operating Voltage)

Rated Maximum

Voltage L-L

(kV)

Rated Withstand

Voltage Impulse

(kV)

Resistive or Transformer

Excitation Current

(Amps)

Bus, Line, or Cable

Capacitive Current

(Amps)

12 110 3.1 1.1

36 200 2.8 1.0

72.5 350 2.2 0.8

1.3.2.1 General

Appropriate safety rules shall be followed, and the subsequent general rules apply:

(a) Instructions and procedures for opening and closing a disconnecting switch, whether by direct hookstick or indirect operating handle, gear box, or power operator, shall be given to every person who will operate the switch.

(b) After operating a switch, each blade shall be checked visually to verify that it is fully closed and latched or fully open, as intended.

(c) Undue force shall not be used to operate a switch. The operating mechanism is designed properly for the switch, and any undue force in the nature of an extension of the operating handle, or an extra person on the operating handle of the switch, may cause severe damage to the switch or operating mechanism. A few sharp raps on the vertical operating pipe or sudden applied tugs on the operating handle may help to free an iced switch mechanism.

(d) Power-operated switches shall be operated to be sure that the switches and their mechanisms and control features are functioning properly. Where circuit conditions will not permit operating an energized switch and where the circuit cannot be de-energized for this purpose, the operating mechanism shall be disengaged from the linkage. The control circuits and mechanism shall be checked in this manner unless the overall adjustments are affected.


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1.3.2.2 Disconnecting

(a) Prior to operating a disconnecting switch, a check shall be made to confirm that no load is being carried by the switch, and that a switch flashover will not extend to the switch operator.

(b) Prior to opening a grounding switch, a check shall be made to determine that operation does not remove necessary safety grounds. Prior to closing, check the circuit to confirm that it is not energized.

(c) Disconnecting switches shall be operated rapidly to reduce arcing time and possible burning of contacts. The operator shall be informed that opening or closing of a disconnect switch may cause arcing in normal switching. It is common practice to use these devices for interrupting small currents such as the charging current of a short length of transmission or distribution line, transformer magnetizing currents, parallel and loop currents, and light load currents. Such operations result in unconfined arcs that, under unfavorable weather or circuit conditions, may cause a system fault. These duties impose varying degrees of severity upon the switch. If circuit interruption is contemplated, care shall be taken to understand the circuit conditions to determine what degree of success may be expected.

(d) Particular regard shall be given to the current magnitude and the transient recovery voltage that will appear across the switch immediately following current interruption. Devices such as arcing horns, quick-break horns, and air or gas blast attachments, are available for extending the interrupting capability of a disconnecting switch. For specific current interrupting applications, the switch manufacturer shall be consulted.

1.3.2.3 Operating procedures for transmission line disconnect switches

Before every operation, verify the following conditions are met.

Operate the switch only if all of these conditions are met:

(a) Switch is grounded according to the design standards.

(b) Wire connection between switch operating handle assembly and ground grid is free from visible corrosion, wear, and broken strands.

(c) Flexible braid connection used for bonding rotating control pipe to the operating handle assembly are free from visible corrosion, wear, and broken strands.

(d) Switch bases, operating pipe, bevel gear (or lever box) assembly, and operating


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handle are securely mounted.

(e) Switch supporting pole is not twisted or warped in a way that could cause operating pipe, handle and linkages to bind.

(f) Line conductors or jumpers are not placing undue strain on the switch terminals that could lead to contact misalignment problems.

(g) Switch and vertical control rod (pipe) insulators are in good condition and clean.

(h) If closed, quick break whips (If any) are in adequate condition and properly seated in catches.

(i) Dispatcher confirms switch has the correct attachments for the type of switching planned:

- Interrupting or picking up transformer magnetizing current. - Dropping or picking up line charging current. - Interrupting or marking parallel (loop) current. - Picking up small amounts of load.

2. Delivery and handling

2.1 Delivery Trucking and handling of power switching equipment, after it is received at its destination, shall be done with due regard based on the fact that porcelain is used in practically all switching equipment and that it is easily broken.

Switching equipment shall be properly stored to protect it from damage. Switches shall be stored in a dry, clean location and shall remain in the shipping container during the storage period.

2.2 Unpacking When unpacking switching equipment, it shall be remembered that many parts are fragile and can be broken by sudden jars and careless handling. Therefore, care shall be exercised to prevent breakage or the distortion of parts of equipment, which could result in trouble, delay, or inconvenience in assembly. All parts shall be inspected before assembly.


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2.3 Assembly and rigging Power switching equipment shall be fully assembled and adjusted before it is placed in position insofar as possible in order to facilitate (minimize) final adjustments.

Rigging, which is used for erecting the equipment, shall be adequate and proper for the equipment involved and shall be attached to the bases unless otherwise instructed by the manufacturer. Lifting by insulator units, contacts or operating parts may cause damage. Attachment shall be made to live or other parts only for stabilizing. Switches shall be secured in the closed position before lifting.

3. Inspection

3.1 Field inspection before operation After the switching equipment has been installed, connected, and adjusted, the insulators, contacts, and moving parts shall be cleaned in accordance with the manufacturer's instructions.

After being installed, but before being placed in service, the equipment shall be carefully inspected, checked, and adjusted in accordance with the applicable drawings. The following are suggested as important inspections and checks:

(a) Examine all insulator units for cracked or defective parts.

(b) Check all contacts for any damage that affects fit, proper pressure, and alignment. If recommended by the manufacturer, lubricate the contacts.

(c) Check all bolted connections for tightness.

(d) Examine all switch locks for security, function, and ease of operation.

(e) Check operating mechanism for proper operation, travel, and recommended lubrication; also check for lost motion or binding, excessive deflection of controls or mounting, and check mechanical connections.

(f) Check the adjustment of horns on horn-gap switches.

(g) As a final inspection, check break distances, clearances between live parts and travel of all switches. Check phase-to-phase clearances and phase-to-ground clearances between live parts of switching equipment and adjacent structures.


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Due to operating criteria and mounting configurations, these switches are not readily serviced at frequent intervals. Inspection of disconnecting switches shall be performed every 3-year. Also, this interval of inspection will depend on atmospheric contamination, use of contamination control coatings, frequency of operation, fault current exposure, etc.

If a switch cannot be maintained on a periodic basis, its service life may be affected. Whenever the switch is operated it shall be opened and closed several times if practicable in order to clean the contacts and free the moving parts.


3.2.2.1 For live-line service and maintenance

A visual inspection of a switch when wet, or the use of a temperature-scanning detector (Thermovision) may indicate hot spots that are possible sources of trouble. Directional microphones or ultrasonic detectors can be used to locate local corona sources on switches, and these sources can then be eliminated during normal switch maintenance.

3.2.2.2 For maintaining de-energized switches

The following procedures are suggested for maintaining de-energized switches.

(a) The switch shall be disconnected from all electric power sources before servicing.

(b) Ground leads or their equivalent shall be attached to both sides of the switch.

(c) Inspect the insulators for breaks, cracks, burns, or cement deterioration. Clean the insulators particularly where abnormal conditions such as salt deposits, cement dust, or acid fumes exist. This is important to minimize the possibility of flashover as a result of the accumulation of foreign substances on the insulator surfaces.

(d) Check the switch for alignment, contact pressure, eroded contacts, corrosion, and mechanical malfunction. Replace damaged or badly eroded components. If contact pitting is of a minor nature, smooth the surface with clean, fine sandpaper (not emery) or as the manufacturer recommends. If recommended by the manufacturer, lubricate the contacts. Inspect arcing horns for signs of excessive arc damage and


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replace if necessary.

(e) Check the blade lock or latch for adjustment.

(f) Inspect all live parts for scarring, gouging, or sharp points that could contribute to excessive radio noise and corona. Check corona balls and rings for damage that could impair their effectiveness.

(g) Inspect inter-phase linkages, operating rods, levers, bearings, etc., to assure that adjustments are correct, all joints are tight, and pipes are not bent. Clean and lubricate the switch parts only when recommended by the manufacturer. Check for simultaneous closing of all blades and for proper seating in the closed position. Check gear boxes for moisture that could cause damage due to corrosion or ice formation. Inspect the flexible braids or slip-ring contacts used for grounding the operating handle. Replace braids showing signs of corrosion, wear, or having broken strands.

(h) Power-operating mechanisms for switches are usually of the motor-driven, spring, hydraulic, or pneumatic type. The particular manufacturer's instructions for each mechanism shall be followed. Check the limit switch adjustment and associated relay equipment for poor contacts, burned out coils, adequacy of supply voltage, and any other conditions that might prevent the proper functioning of the complete switch assembly.

(i) Inspect overall switch and working condition of operating mechanism. Check that the bolts, nuts, washers, cotter pins, and terminal connectors are in place and in good condition. Replace items showing excessive wear or corrosion. Inspect all bus cable connections for signs of overheating or looseness.

(j) Inspect and check all safety interlocks while testing for proper operation.


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Disconnecting Switches Inspection Report Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site Disconnecting Switch ID




1. Cracked or defective parts of insulator unit

2. Check contact and lubricate contact if needed

3. Tightening of bolted connections

4. Switch locking system Basis value: 30kV


6. Adjustment of horns on horn-gap switches

Field

inspection

before

operation

7. Break distances, clearances between all switches

1. IR scan Energized condition

2. Directional microphones (or Ultrasonic detector) Energized condition

3. Cracked or defective parts of insulator

4. Switch contact condition

5. Blade lock or latch condition

6. All live part condition and corona balls (rings)

7. Mechanical interlocking system

8. Power-operating mechanism assembly

Routine

inspection


Remark




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V. Surge Arrester


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1. General

1.1 Description A surge arrester is a protective device for limiting surge voltages on equipment by discharging or bypassing surge current. Surge arresters allow only minimal flow of the 50-hertz-power current to ground. After the high-interval lightning surge current has been discharged, a surge arrester, correctly applied, will be capable of repeating its protective function until another surge voltage must be discharged.

The technology of surge arresters has undergone major changes in the last 100 years. In the early 1900’s, spark gaps were used to suppress over voltages. In the 1930’s, the silicon carbide replaced the spark gaps. In the mid 1970’s, zinc oxide gapless arresters, which possessed superior protection characteristics, replaced the silicon carbide arrester.

1.2 Types of surge arrester Surge arresters used for protection of exterior electrical distribution lines will be either of the metal oxide or gapped silicon carbide type. Expulsion-type units are no longer used.

1.2.1 Gapped silicon carbide type

Silicon carbide has more nonlinearity than zinc oxide. Without a gap the increase in leakage current, because of this nonlinearity, would soon burn out the arrester. A gap prevents burnout, but it does mean that the arrester will not operate until the gap sparks over.

Silicon carbide arresters are vulnerable to moisture ingress that leads to failure due to reduction in spark over. Contamination can also upset voltage distribution resulting in spark over reduction. Over a period of time, excessive energy inputs can destroy the ability of the blocks and gaps to interrupt follow current leading to failure of the arrester.

1.2.2 Metal oxide type

The metal oxide arresters are without gaps, unlike the SIC arrester. This “gap-less” design eliminates the high heat associated with the arcing discharges. The metal oxide varistor (MOV) arrester has two-voltage rating: duty cycle and maximum continuous operating voltage, unlike the silicone carbide that just has the duty cycle rating. A metal oxide surge


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arrester (MOSA) utilizing zinc oxide blocks provides the best performance, as surge voltage conduction starts and stops promptly at a precise voltage level, thereby improving system protection. Failure is reduced, as there is no air gap contamination possibility; but there is always a small value of leakage current present at operating frequency.

Therefore, GECOL uses Metal Oxide Arrester as surge arrester in the field.

Figure 7 Comparison of silicon Carbide and Metal Oxide arrester

1.2.3 Polymer/Porcelain Arrester

Polymer arresters are gaining in popularity over the porcelain arresters. When a reclose operation occurs and the fault has not cleared, the arrester is subjected to a second fault current. This second operation often leads to arrester explosion since the porcelain had already been weakened by the first fault. If the pressure relief rating of the arrester is exceeded, the arrester may fail violently, since it cannot vent the excess gasses. This type of failure can lead to other equipment being damaged or injury to personnel who may be in the vicinity of the failure. Due to the ability of the polymer station arrester to vent out the side, the housing is not weakened when exposed to the fault current. Therefore a polymer arrester can be reclosed on multiple times without the fear of a violent failure.

The polymer arresters are less expensive than the porcelain arrester and appear to avoid some of the in service problems, such as moisture ingress, that often occur in porcelain

Shunt Resistor

Valve Element

Gap

Silicon Carbide Metal Oxide

Older Design (MCOV & MOV) Newer Design


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arrester. One manufacturer reports that moisture ingress is the direct cause of failure in 86% of all failures.

Figure 8 Polymer Arrester Figure 9 Porcelain Arrester

1.3 Structure

Line terminal

Spring

Rubber packing

ZnO element

Fixing band

Connected pipe

Stainless cap

Disconnecter

Earth terminal

Porcelain housing


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1.4 Rating

Nominal discharge current

10,000 A 5,000 A 2,500 A

Maximum residual voltage

Rated

voltage

(kV)

Steep Lightning Switching Steep Lightning Steep Lightning

12 31.2~48 27.6~43.2 24~34.8 32.4~48 28.8~43.2 48 43.2

36 93.6~133.2 82.8~118.8 72~93.6 97.2~133.2 86.4~129.6 144 129

72 187.2~266.4 165.6~237.6 144~187.2 194.4~266.4 172.8~259.2 N/A* N/A*

Note: The unit of the Maximum residual voltage is kVpeak

* : Not available

1.5 Classifications of surge arrester Surge arresters are classified by their standard nominal discharge currents and they shall meet at least the test requirements and performance characteristics.

Table 13 Arrester classification

Standard nominal discharge current a Classification

20,000A 10,000A 5,000A 2,500A 1,500A

Rated voltage Ur

(kVrms) 360 <Ur ≤ 756 3 ≤ Ur ≤ 360 Ur ≤ 132 Ur ≤ 36 b

a. It is customary to classify arresters as follows:

- Station for 10,000A and 20,000A arresters

- Intermediate or distribution for 5,000A arresters

- Secondary for 1,500A arresters

b. This low-voltage range is under consideration.


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1.6 Ground resistance value of surge arrester

Table 14 Ground resistance value of surge arrester

Voltage level Object to be protected Ground resistance value (Ω)

Substation facilities 5 66kV

Line facilities 20


Line facilities 20


Line facilities 20

2. Delivery and storage (a) When delivered or moved, surge arresters must be loaded with less than 5 stacks.

(b) Falling of surge arresters would have a bad influence on the quality of surge arresters.

(c) Surge arresters should be stored in sufficiently dried condition and in a room where dusts don’t occur. Storage in outdoor condition or in corrupted circumstance for long time could have a bad influence on proper performance of them.

※ Handling Suspect Arresters: • A damaged seal-gapped arrester should be handled with care. Due to increased

pressure caused by the destruction of internal elements, a defective arrester may become an explosive hazard.

• If the decision is made to perform an internal inspection of the failed arrester, be assured that the arrester has vented properly

• Do not “throw away” a defective arrester – the arrester should be properly vented before disposing

3. Inspection Modern surge arresters require little operational maintenance and the degree to which such maintenance can be done is normally limited by lack of adequate test equipment. This limits surge arrester maintenance to visual inspection and simple electrical tests. It is


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recommended that units found to be defective be replaced rather than repaired: Where an arrester is composed of two or more individually complete units, each unit should be tested separately. Thus, a bad unit may readily be replaced and the good units retained. Surge arresters are almost always applied with one terminal connected to an electrically energized source and one terminal to ground. No work should be done, or contact made with surge arresters, when connected to the energized source.

Visual inspection will not always detect a damaged arrester. Interior damage may result from a broken element, presence of moisture, a severe direct lightning stroke, or the use of an arrester with an incorrect rating. Sometimes these conditions will cause radio interference. Special inspection, to detect inferior arrester units, may be made either in the field or shop. Tests must be made strictly in accordance with manufacturer’s recommendations, and the results interpreted in line with manufacturer’s criteria.

3.1 Substation class arrester

3.1.1 Field inspection before operation

Before and after installation, the surge arrester should be carefully inspected about following items.

(a) Cracks, chips, contamination, damages on the arrester housing

(b) Measuring of ground resistance value

(c) Insulation condition of the primary and secondary side

(Insulation resistance measurement)

(d) Terminal connections condition on the primary and secondary side

(e) Approved design specification

3.1.2 Initial inspection 3.1.2.1 Interval of inspection

Surge arresters first installed in the field shall be inspected within 1 year since in operation.

3.1.2.2 Inspection method Inspection items of initial inspection should be applied in correspondence with routine inspection.


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3.1.3 Routine inspection 3.1.3.1 Interval of inspection

Routine inspection of surge arresters shall be performed on 3-year cycle or whenever necessary.

3.1.3.2 Inspection method Routine inspection should be made periodically using following tests. (a) Meggar test (b) Leakage current test (c) Infrared analysis

3.2 Distribution class arrester 3.2.1 Field inspection before operation

Before and after installation, the surge arrester shall be carefully inspected in the same way as the substation class arrester like 3.1.1

3.2.2 Routine inspection

3.2.2.1 Interval of inspection

Routine inspection of surge arresters shall be performed at the same period as patrol or whenever necessary.

3.2.2.2 Inspection method

(1) Visual inspection should be made to ensure that: (a) The line lead is securely fastened to the line conductor and the arrester. (b) The ground lead is securely fastened to the arrester terminal and ground. (c) The arrester housing is clean and free from cracks, chips, or evidence of external

flashover. (d) The arrester is not located in such a manner as to be subject to:

• Damaging fumes or vapors. • Excessive dirt or other current-conducting deposits. • Excessive humidity, moisture, dripping water, steam, or salt spray. • Abnormal vibrations or shocks. • Ambient temperatures in excess of 55 ºC.

(e) Any external gaps are free from foreign objects and set at proper spacings. (2) Infrared analysis


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4. Test method

4.1 Megger test A megger test is the most usually used for testing surge arrestors. It could simply measure the insulation resistance of surge arrestors. Such a test may indicate shorted valve elements in valve-type arresters. This test can be made to provide additional information on the condition of arresters. But the insulation resistance value of deterioration judgment standard depends on manufacturer and type of surge arrestor. Therefore it is necessary to perform the inspection on the basis of the insulation resistance value the manufacturer recommends.

4.2 Leakage current test Any deterioration of the insulating properties of a metal oxide arrester will cause an increase in the resistive leakage current or power loss at given values of voltage and temperature. The majority of diagnostic methods for determining the condition of gapless metal oxide arresters are based on measurements of the leakage current.

The measuring procedures can be divided into two groups: on-line measurements, when the arrester is connected to the system and energized with the service voltage during normal operation, and off-line measurements, when the arrester is disconnected from the system and energized with a separate voltage source on site or in a laboratory.

Measurements off-line can be made with voltage sources that are specially suited for the purpose, e.g. mobile AC or DC test generators. Good accuracy may be obtained by using the off-line methods, provided that a sufficiently high test voltage is used. The major disadvantages are the cost of the equipment and the need for disconnecting the arrester from the system.

Measurements carried out on-line under normal service voltage are the most common methods. For practical and safety reasons, the leakage current is normally accessed only at the earthed end of the arrester. To allow measurements of the leakage current flowing in the earth connection, the arrester must be equipped with an insulated earth terminal.

NOTE: The insulation of the earth terminal must, also after long-term degradation, be sufficient to prevent circulating currents caused by electromagnetic induction, since these currents may interfere with the measurement of the leakage current.


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On-line leakage current measurements are usually made on a temporary basis using portable or permanently installed instruments. Portable instruments are usually connected to the earth terminal of the arrester by means of a clip-on, or permanently installed, current transformer.

Long-term measurements of the leakage current may be necessary for closer investigations, especially if significant changes in the condition of an arrester are revealed by temporary measurements. Remote measurements may be implemented in computerized systems for supervision of substation equipment.

Measurement of leakage current of metal oxide arresters may be carried out by two methods largely. For more complete detailed instructions on the methods of measurement and procedure, please see the appropriate leakage current measuring instrument manual.

The two measurement methods are as follows

(1) Measurement method of the total leakage current

(2) Measurement method of the resistive leakage current

The measured leakage current data may be compared with information supplied by the arrester manufacturer. To utilize this information, it is important that the operating voltage and the ambient temperature are known at the time of measurement. For efficient use of the diagnostic methods described above, the arrester manufacturer may provide information relevant to the various methods. The information may be comprised of the resistive current, third harmonic current and power loss data for each arrester type as functions of voltage and temperature.

NOTE: Due to the complexity of the measurement methods, it is recommended that the arrester manufacturer be consulted in order to avoid misinterpretation of the measurement results.

4.3 Infrared analysis Infrared analysis of the arrester is gaining in popularity and has been used with good results in identifying higher than normal current flow through the metal oxide components. Routine testing on a normal basis is recommended in hopes of identifying and replacing defective arresters before equipment damage or personal injury.


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Figure 10 Example of surge arrester 10 °C above Ambient

Problem classification Temperature rise of subject component above the adjacent

conductor

Minor Less than 5 ºC

Intermediate 5 ºC to 10 ºC

Serious 10 ºC to 16 ºC

Critical More than 16 ºC

Table 15 Infrared analysis basis


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Surge Arrester Inspection Report

Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site Arrester ID

Type Rating


Inspection result Item

A phase B phase C Phase Remark

Condition of arrester housing

Connection of line lead

Connection of ground lead

Connection with equipment

Condition of arrester location

External

Inspection

Condition of Bracket, Basement

Ground resistance value

Insulation resistance value

(each phase – ground)

Leakage current (mA)

Testing

Infrared Analysis

Remark

Foreman : Office/Section supervisor: :

Signature : Signature :

Date : Date :


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VI. Storage Batteries


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1. General

1.1 Description The battery is at present the most practical and widely used means of storing electrical energy. The storage capacity of a battery is usually defined in ampere-hours (Ah). Batteries can be classified into primary and secondary types. A primary battery stores electrical energy in a chemical form which is introduced at the manufacturing stage. When it is discharged and this chemically stored energy is depleted, the battery is no longer serviceable.

A secondary or rechargeable battery absorbs electrical energy, stores this in a chemical form and then releases it when required. Once the battery has been discharged and the chemical energy depleted, it can be recharged with a further intake of electrical energy. Many cycles of charging and discharging can be repeated in a secondary battery.

Storage batteries as secondary batteries are used in exterior facility electrical distribution systems to provide a power supply to devices whose control response will be damaged by an electrical system power outage. This chapter describes station batteries as they are generally called, as opposed to uninterruptible power system batteries or automotive type batteries. A storage battery is composed of one or more rechargeable electrochemical type cells. Systems are designed for full-float operation, with a battery charger to maintain the battery in a charged condition. Batteries used for control of substation and power equipment are required to provide low currents for long periods and high currents for short periods. A battery’s reserve capacity requirements are based on a duty cycle (usually an 8-hour operating time period) when all continuous and momentary loads must be supplied by the battery with no recharging available from the battery charger.

1.2 Types of storage battery The two electrochemical types in general use for station batteries are lead-acid and nickel-cadmium. Construction types include vented (flooded) and valve-regulated (sealed) units.

There are five basic components to a battery cell: the container, the positive plate (electrode), the separator or retainer, the negative plate (electrode), and the electrolyte.

1.2.1 Lead-acid units


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Lead acid batteries have an acidic electrolyte solution of sulfuric acid (H2SO4). The active materials used are lead dioxide (PbO2) for the positive plate, and sponge lead (Pb) for the negative plate. The active materials for both the positive and negative plates are incorporated in a plate structure composed of lead or a lead alloy. Their nominal battery voltage is defined as 2.0 volts per cell.

1.2.2 Nickel-cadmium units

Nickel cadmium batteries use an alkaline electrolyte (potassium hydroxide). The active materials used are nickel hydroxide for the positive plate and cadmium hydroxide for the negative plate. Their nominal battery voltage is defined as 1.2 volts per cell.

1.2.3 Vented batteries

Vented (flooded) cells are constructed with the liquid electrolyte completely covering (flooding) the closely spaced plates, so that there is a large volume of free electrolyte. The electrolyte maintains uniform contact with the plates. Vented units are characterized by a removable vent cap which allows the electrolyte to be checked and adjusted as needed. Overcharge will produce gases which vent through the cell, requiring regular water replacement. Vent caps must be accessible, so batteries are larger than valve-regulated types and are provided with flame arresters. Gassing requires ventilation to avoid explosive possibilities and possible corrosive damage to battery terminals.

1.2.4 Valve-regulated batteries

Valve-regulated cells are sealed, with the exception of a valve that opens periodically to relieve excessive internal pressure. To limit water consumption, cells are designed to provide recombination of charge gases by passing oxygen evolved from the positive plate over the negative plate, where the recombination reaction occurs. The valve regulates the internal pressure to optimize recombination efficiency (hence the term valve-regulated). The valve opens when the cell’s internal pressure exceeds a set limit and once the pressure is relieved the valve closes and reseals. No cell check of an electrolyte level nor the specific gravity of each cell is required. Outgassing of these batteries is low at normal charge rates, but it can occur when there is a battery or battery charger failure. Cells can pose a hazard if enclosed so as to inhibit cooling air, or installed so as to place them in the heat flow of electronics which may occupy the same enclosure.


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1.3 Nickel-Cadmium Cell Batteries Vented nickel-cadmium rechargeable batteries for stationary equipment shall be generally used as station batteries of GECOL.

1.3.1 Description of nickel-cadmium batteries

The nickel-cadmium technology results in more expensive batteries but these batteries are resistant to mechanical and electrical abuse, and will operate well over a wide temperature range, and can tolerate frequent shallow or deep discharging.

1.3.2 Strong and week point of nickel-cadmium batteries

1.3.2.1 Strong point

(a) Internal resistance is small, a large current discharging is available, and the rate of capacity reduction is small.

(b) Service life is long due to no sulphation and no leakage of the active materials.

(c) Corrosive gas doesn’t occur and the measurement of specific gravity is not required.

(d) It is strong to a vibration or a impact because mechanical intensity of plate is large.

(e) It is suitable for mobile because its efficiency of weight is large.

(f) Maintenance work is small because influences by over-charge, over-discharge, long term storage is small.

NOTE 1: Weight efficiency means the output of power per 1kg of battery weight. Stationary battery is 10 to 15 Wh/kg, mobile battery is 20 to 30Wh/kg, alkaline battery is 20 to 30 Wh/kg.

NOTE 2: Alkaline used as an electrolyte is not directly related to charging or discharging like lead acid battery but responsible for transferring ions, so that there is no variation of specific gravity by charge and discharge.

1.3.2.2 Weak point

(a) The rate of voltage variation is large during the storage.


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(b) The using rate of the active materials is bad

(c) Economical efficiency is low because electromotive force per unit is lower than lead acid battery.

1.3.3 Flooded cells

These units utilize plates made of nickel-oxide for the positive electrode and cadmium for the negative electrode. The electrolyte is an alkaline solution of potassium hydroxide which does not take part in the cell reaction. Accordingly, its specific gravity does not change during charge or discharge, and the electrolyte retains its ability to transfer ions irrespective of the charge level. The majority of cells used in station battery applications are of the vented type. During discharge, vented-type cells can produce hydrogen gas and oxygen gas in a potentially explosive mixture which must be adequately exhausted. Since the gas is free from corrosive vapors, a dedicated battery room is not required, although it is still recommended.


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1.4 Structure (Vented nickel-cadmium cell battery)

1.5 Requirements for nickel-cadmium batteries The nickel-cadmium electrolyte is a solution of potassium hydroxide in water with a specific gravity between 1.180 and 1.200, depending upon the manufacturer. The electrolyte does not enter into the reaction of the nickel-cadmium cell. Therefore specific gravity is not an indication of state-of charge and specific-gravity readings are not part of normal routine

Flame arresting vent

Plate group bus

Connects the plate tabs

with the terminal post.

Plate tabs and terminal

posts are projection welded

to the plate group bus

Plate tab

Connects the plate tabs

with the terminal post.

Plate tabs and terminal

posts are projection welded

to the plate group bus

Plate

Horizontal pockets

of double-perforated

steel strips

Separating grid

These separate the

plates and insulate

the plate frames

from each other.

The grids allow

free circulation of

electrolyte between

steel plates

Plate frame

Seals the plate pockets and

serves as a current collector

Terminal seal

This is mechanically clipped and provides

an excellent seal. This minimizes carbonation deposit


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maintenance. If readings are taken, the temperature correction for the electrolyte is the same as for lead-acid batteries. The electrolyte in a nickel-cadmium cell with a specific gravity of 1.190 will start to freeze (slush) at approximately minus 23 ºC. Occasionally, grayish-white deposits of potassium carbonate may be seen on the cell tops. These deposits form because the electrolyte entrained in the escaping gas reacts with the carbon dioxide in the air. Although not corrosive, this deposit is a conductor when damp and needs to be removed from the battery.

1.5.1 Parameters

Float voltages for nickel-cadmium cells are significantly different from those for lead acid cells. For the same battery terminal voltage, the number of cells will be greater, because a lead acid battery is a nominal 2-volts per cell while a nickel-cadmium battery is a nominal 1.2-volts per cell. Degradation of nickel-cadmium batteries or excessive capacity loss is indicated when the battery capacity has dropped more than 1.5 percent of rated capacity per year from its previous performance test capacity.

1.5.2 Temperature

Nickel-cadmium batteries are less affected by temperature than lead-acid batteries. They can sustain high temperatures more easily, because the chemistry in the active materials is relatively stable. For example, at 32 ºC the normal life of a nickel-cadmium cell is reduced by about 20 percent, compared with a reduction of about 50 percent for a lead-acid cell. With a normal electrolyte, the battery will operate at temperatures as low as minus 30 to 40 ºC. With a higher specific gravity electrolyte, it will operate at even lower temperatures. The available capacity is reduced at low temperatures, but at minus 40 ºC a nickel cadmium battery can still deliver 60 percent or more of its rated capacity.

1.5.3 Memory effect

Nickel-cadmium cells charged at very low rates are subject to a condition known as a “memory effect.” Repeated shallow cycling, to approximately the same depth of discharge, leads to continual low-rate charging and results in a loss of surface area in the negative active material, due to the growth of large crystals. This increase in the cell’s resistance produces a grater voltage drop. The result is a reduction in the effective reserve time of the system. The memory effect can be erased by providing a complete discharge followed by a full charge with constant current. This breaks up the crystalline growth on the plates. The


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conditions of station operation will rarely lead to this type of cycling, but users should be aware of the cause and the cure.

1.5.4 Electrolyte level

Vented type units will need to have the electrolyte level checked, even though a specific gravity reading may not be required.

1.5.4.1 Electrolyte level

Caution must be taken when handling the electrolyte. The electrolyte level in all cells should be checked monthly. The maximum level of the electrolyte is halfway between the tops of the plates and the inside of the cell covers. (Do not include vent heights.) The level can be checked visually if the cell containers are transparent. If not, the level may be determined by inserting an electrolyte-level test tube (plastic or glass) through the vent until it rests on top of the plates. Then place a finger tightly over the exposed end, and withdraw the tube for inspection. The electrolyte must always be returned to the cell from which it was withdrawn. When the electrolyte level is low, distilled water should be added to restore the electrolyte to the proper level, but the cell should not be overfilled. If the cells are overfilled, the electrolyte will be forced out of vents during charging and will saturate trays. This causes electrolysis between the cells, corrosion of the cell containers, and troublesome grounds in the electrical circuit. Overfilling the cells will also dilute the electrolyte to such an extent that the battery’s specific gravity will be reduced and cell plates will be damaged.

1.5.4.2 Electrolyte renewal

When electrolyte is clear and colorless, it is in good condition. Electrolyte that has become contaminated with small quantities of carbon dioxide from the air will form potassium carbonate and will appear cloudy. If the solution becomes colored or cloudy, it is evident that the electrolyte is contaminated with impurities and should be changed. It may also become necessary to change the electrolyte due to overcharging or overflow, which cause the specific gravity to fall outside the manufacturer’s specified range. If the specific gravity is low, continued operation will result in a rapid reduction in the life of the battery. Therefore, when the specific gravity falls below 1.170, the electrolyte should be changed. Follow the manufacturer’s instruction when renewing the electrolyte. The battery warranty may not permit renewal without the manufacturer’s permission.


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1.5.4.3 Charging

Specific gravity or cell voltage readings generally cannot be used to determine the state of charge of a nickel-cadmium battery. To ensure that the battery is fully charged, it should be given a booster charge once a month, after any heavy or intermittent discharges, or after the battery charger has been out of service. Maintenance personnel should maintain a record of the monthly booster charges. The accuracy of the charger voltmeter should be checked against a recently calibrated voltmeter at least once a year.


2.1 Delivery Personnel should be aware of the potential dangers of working on or near batteries, use caution, and wear appropriate personal protective equipment at all times.

When moving a battery from the battery storage room to the installation location, use designated battery pallets, and a vehicle on witch they can be safely secured without hazard to employees or the public. Take precautions to protect the battery from being short-circuited and to prevent electrolyte from being spilled during delivery. Be sure the shipping caps are installed if applicable.

Display “Corrosive” labels when delivering batteries.

2.2 Storage Follow these steps to store batteries after acceptance.

2.2.1 Storage after acceptance

(a) After the battery has been tested and accepted, store it (normally without float charging) in a clean, level, cool, and dry location.

(b) Fill out and insert a storage battery inventory card in the card holder.

(c) Apply an initial charge referring to manufacturer’s literature for information on initial charges.


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2.2.2 Storage after removal from service

(a) When a battery is removed from service, perform a capacity test if one has not been performed within the previous 12 months.

• If the capacity is less than 80%, retire the battery.

• If the capacity is greater than 80%, store the battery.

(b) After the battery has been tested and accepted, store it without float charging in a clean, level, cool, and dry location.

(c) Fill out and insert a storage battery inventory card in the card holder.

(d) Apply an initial charge referring to manufacturer’s literature for information on initial charges.

3. Inspection

3.1 Initial inspection Initial inspection tests may be carried out in the field, preferably after the battery has been on float charge for at least 12 weeks without discharging. Although a field inspection test carried out after less than 12 weeks on float charge will confirm that a battery has adequate capacity, the acceptance test results cannot easily be compared with future performance test results because of the float effect. Field tests should be made at a specific discharge rate and for a duration relating to the manufacturer’s rating or to the purchase specification’s requirements.

3.2 Routine inspection Routine inspections of storage batteries should be made under normal float conditions. Inspection of the battery should be performed on a regularly scheduled basis. The interval should be selected depending on site conditions, charging equipment, and monitoring devices providing remote indications of abnormal operations.

3.2.1 Monthly

Provide recorded checks of the following data:


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(a) Check float voltage measured at the battery terminal.

(b) Observe general appearance and cleanliness of the battery, the battery rack, and battery area.

(c) Check battery charger output current and voltage.

(d) Check electrolyte levels.

(e) Check for cracks in cells or leakage of electrolyte.

(f) Check for any evidence of corrosion at terminals, connectors, or racks.

(g) Check condition of ventilation equipment.

3.2.2 Semiannually

In addition to the monthly items, provide recorded checks of the following data:

(a) Provide a detailed visual inspection of each cell.

3.2.3 Yearly

In addition to the Semiannually items, provide recorded checks of the following data.

(a) Check integrity of the battery rack

(b) Check intercell connection torque

(c) Check condition and resistance of cable connections

Intercell connection torque should be checked at least once after the initial installation. In vibration-free environments, subsequent checks may be performed in accordance with the manufacturer’s recommendations. Intercell connection resistance readings may be substituted for connection torque checks, if the cell design allows. Consult the manufacturer of the battery and/or test equipment for details.

3.3 Special inspection Special inspection of storage batteries should be made at least once each 3-years or whenever a battery experiences an abnormal condition (such as a severe discharge or overcharge) to ensure that the battery has not been damaged. This inspection should include


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capacity test as well as all annual inspection items

NOTE: Do not overtest. Frequent testing will shorten the service life. Subsequent performance tests are recommended at 5-year intervals, until the battery shows signs of degradation or has reached 85 percent of the service life expected.

4. Test methods

4.1 Tools and devices Special equipment may be available or may be rented, dependent upon the site’s maintenance capabilities. Normal test equipment and safety equipment should already be available as a part of the electrical maintenance equipment. The use of safety equipment to protect personnel is mandatory; it should be available to maintenance personnel at all times. Periodically, recalibrate all devices as necessary. A number of new instruments are available which can continuously monitor a battery. These are often provided for systems serving very critical loads. One final caution is that instruments inserted into electrolyte should not be used for different battery types. For example, a hydrometer used on a lead-antimony battery should never be used on a lead-calcium or a nickel-cadmium battery. This cross use of equipment will cause cell contamination.

(a) Goggles and face shields

(b) Chemical-resistant gloves

(c) Protective aprons and overshoes

(d) Portable or stationary water facilities for rinsing eyes and skin in case of contact with alkaline electrolyte. The use of pH buffered neutralizing eyewash solution is recommended.

(e) Spill absorbing/neutralizing materials, or other suitable neutralizing agent recommended by the manufacturer for alkaline electrolyte spillage.

(f) Adequately insulated tools.

(g) Lifting devices of adequate capacity, when required.

(h) Battery capacity tester set


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(i) Battery conductance tester set

(j) Metering of DC (located on the battery charger)

(k) Micro-ohmmeter set

(l) Hydrometer set

(m) Portable infrared temperature measuring device

(n) Terminal protective grease

(o) Torque wrench

(p) Rubber matting

4.2 Visual inspections of batteries Visual inspections will indicate when cleaning is necessary and afford the opportunity to check cells for damage or evidence of improper charging or other mishandling. A flashlight or other localized unsparking light source is essential for inspecting cell components and connections and for checking for evidence of excessive gassing, mossing, sediment, and low electrolyte levels. Check that there is no battery vibration. Under abnormal operating conditions, hydration and frozen electrolytes can occur and if not recognized could cause irreparable damage.

4.2.1 Cell and connection inspections

The jars, plates, and connections should be closely inspected on each cell.

(1) Jars

Jars, covers, and cover-to-jar and cover-to-post seals should be checked for cracks or other structural damage. Failure of any seal will cause the electrolyte to seep out. A light source can be directed through clear jars to locate cracks or structural damage to the jar, cover, and seals. Such defects should be noted and the manufacturer should be consulted for remedial action.

(2) Plates

Unwrapped plates in a clear jar should be examined, as they show the battery’s condition.

The color of the positive plate of the cell will vary from light- to deep-chocolate brown. The darker the color the most likely the battery has been overcharged. The negative plate will be gray in color, with a tendency to darken with age. Check and note any buckling, warping,


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scaling, swelling, or cracking of plates.

(3) Battery terminals

Battery terminals may be inspected using a current/resistance (IR) probe. A connection carrying current with resistance will heat up. Retorquing cell connections without justification will lead to failure. If connection is loose or has high resistance (heating) it must be disassembled, cleaned and reassembled, including torquing. If the nut does not turn on the bolt freely, the bolt and nut must be replaced. A connection carrying current without heating does not need to be retorqued. A connection which is heating needs to be cleaned.

(4) Other checks

Check for electrolyte spillage, evidence of corrosion, and vent cap damage, and correct any problems. Examine cables connecting the battery to the battery charger to ensure there is no strain on the cell posts, and to check that terminal posts and connections are clean.

4.2.2 Excessive gassing

Although some gassing on recharge is normal, excessive gassing can indicate overcharging, and should always be noted. Outgassing, when a cell is on open circuit or on float charge, may be an indication of high local action and undercharging. On the other hands, cells which do not gas during charge may indicate problems such as undercharge, short circuits in the cell, or impurities in the electrolyte.

4.2.3 Mossing

Mossing of nickel-cadium cells is caused by overcharging, or charging at excessively high rates. The manufacturer may provide moss shield protection on the top of the plates for some cell constructions. Mossing results from the accumulation of a sponge-like material on top of the negative plates or straps. The material is shed predominantly from the positive plates and is carried off by gassing. If deposited on the positive plates, gassing simply washes it off again, but the material will adhere if deposited on the negative plates. Over time, the negative plates build up a sufficient deposit to bridge and make contact with positive plates, causing partial shorts. If mossing is found during an inspection, expect to find excessive sediment as well.

4.2.4 Sediment

Observing quantity and color of sediment in clear nickel-cadium battery jars also indicates the battery’s condition.

(1) Excessive sediment


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Excessive sediment usually indicates overcharge or charge at excessively high rates. The sediment from a well maintained cell may look like a layer of dust on the bottom of the jar. The sediment from a poorly maintained cell may completely fill the space provided under the plates and resemble hills. Partial short circuits will occur when the sediment hills reach the plate bottoms.

(2) Color of sediment

Dark or chocolate brown sediment hills beneath the positive plates indicates continuous overcharge. Gray sediment in hills beneath the negative plates indicates continuous undercharge. Excessive but somewhat mixed sediment hills, showing both positive and negative materials, indicate the battery has probably undergone random periods of undercharge and overcharge. Where excessive sediment is noted, examine cells for mossing.

4.2.5 Battery racks

Battery racks should be checked during visual inspections. Included are checks for structural integrity, corrosion, and proper grounding.

(1) Corrosion

The jars normally rest on corrosion-resistant supports or plastic jar supporting channels installed on the rack structure. Check these and all items composing the rack for corrosion.

(2) Seismic

If the battery rack is a seismic type for installations requiring earthquake protection, additional checks of the rails and spacers must be made. Seismic racks use rails and spacers to prevent movement of cells during an earthquake, and the spacers function to prevent adjacent cells from knocking together. The side rails are covered by a corrosion-resistant cover (such as a plastic channel) where they touch the jars. Check to ensure that all side rails, end rails, and spacers are in place, and that bolts are properly torqued. Portions of the rack seismic equipment may occasionally be disassembled to allow maintenance to be performed on the battery or for cell replacement. The ability of the rack to protect the battery during an earthquake will be impaired if rack reassembly is not properly tightened.

(3) Grounding

Check that ground connections are correct, tight, and uncorroded.

4.2.6 Damaging actions to be noted

Low electrolyte levels, vibration, hydration, or frozen electrolyte can often damage batteries beyond repair ability and such batteries should be noted for prompt replacement.


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4.2.7 Low electrolyte levels

Water should be added to cells when inspection reveals electrolyte levels below the high level line. The manufacturer should be consulted immediately about cells where the electrolyte level is below the plate tops. Water should not be added to these cells until the manufacturer has agreed that this is the proper action or has inspected the cells and recommended filling. Electrolyte levels below the plate tops can cause permanent cell damage, and the cell may need to be replaced. A record of the amount of water added to each cell should be kept and checked with the battery manufacturer’s normal cell water consumption requirement. Water consumption in excess of the manufacturer’s requirement is an indication of overcharging. A cell that has been recently moved or transported should not have water added until it has been placed back on charge for the period of time recommended by the manufacturer. If the plates were exposed while moving cells, consult the manufacturer for recommended action. Vibration during movement will tend to free hydrogen bubbles attached to the plates. The loss of these bubbles will cause a decrease in the electrolyte level. Once the cell is installed, the bubbles will reappear, and the electrolyte level will increase. Never add alkali to a cell, nor any additive which claims to rejuvenate cells.

(1) Vibration

Check the surface of the electrolyte for indication of any battery vibration. Battery life will be reduced in proportion to the length of time and action of any severe systematic vibration. Excess sediment, when there is no apparent reason for that sediment (the battery has not experienced overcharging or undercharging), can indicate recurrent vibration. Where signs indicate vibration, reexamine the battery supporting/restraining system and eliminate this source of damaging activity.

(2) Hydration

Overdischarge of a nickel-cadmium battery without immediate recharge can cause hydration. This can happen if the battery charger is shut down or if a nickel-cadmium battery is kept in storage for an extended period without recharging. The cell must be replaced if irreversible damage is indicated, for example, by a whitish “bathtub ring” visible approximately halfway up a clear jar. The lead and lead compounds in the cell dissolve in the water released during over-discharge and form lead hydrate, which is deposited on the separators. Thousands of short circuits between the positive and negative plates will occur when the battery is recharged after hydration.


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4.3 Connection resistance measurement A connection resistance check is very important but is often neglected, even though it can be conducted with the battery in service. The instruments normally used are the same as those used to measure a power circuit-breaker’s contact resistance. A moderate to high current is passed through the connection under test and the voltage drop is measured and converted at the meter output to microhms. The test, performed at the initial installation, should be repeated periodically and the results compared. High connection resistance, if not detected, can cause severe damage, especially in a stationary cell required to discharge at a high current rate for a period of time. High connection resistance can actually melt battery posts.

4.4 Capacity tests The only true indication of battery condition and capacity is a discharge test. Stationary cells designed for float operation should have no more than two deep discharges per year. The duration of these tests, test setup, personnel needed, and other requirements make frequent testing impractical. Another consideration is that the battery is not available to serve its load during a capacity test, requiring a system protective shutdown or provision of a redundant or replacement battery.

For these reasons, voltage tests are used to periodically monitor the battery condition. Recognize that these readings indicate state-of-charge, but do not indicate the capacity of the battery.

(1) Use of capacity tests

The results of the capacity test can be used to determine the need for a replacement battery. Three types of battery capacity tests are described in the standards: acceptance, performance, and service tests. Of these, the last two are required for normal maintenance testing.


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Figure 6 Battery Capacity Testers

(2) Comparison of results

It is important to compare the results to prior test data to establish a trend. Battery capacity may be less than 100 percent of nameplate rating during the first few years of operation, unless 100 percent capacity at delivery was required by the purchase specification. The capacity of a new battery (normally 90 to 95 percent of nameplate) will rise to its rated value after several charge-discharge cycles or after several years of float operation.

5. Charging of nickel-cadmium batteries

5.1 Battery charging precautions Batteries are normally connected to their permanent charging equipment, but there may be occasions where testing or charging of new batteries requires connection to a test-shop charging device.

(1) All charging

The following precautions will always be taken:

(a) Use tools with insulated handles.

(b) Prohibit smoking and open flames, and keep possible arcing devices removed from the immediate vicinity of the battery.

(c) Ensure that the load test leads are connected with sufficient cable length to prevent


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accidental arcing in the vicinity of the battery.

(d) Ensure that all connections to load test equipment include short-circuit protection.

(e) Ensure that battery area ventilation is operable.

(f) Ensure unobstructed egress from the battery area.

(g) Avoid the wearing of metallic objects such as jewelry.

(h) Remove vent plugs from cells only to take readings or add water.

(i) Ensure that there are no unintentional grounds.

(2) Test-shop charging

Use only direct-current equipment having the proper voltage. Connect the positive terminal of the charging circuit to the positive terminal of the battery and the negative terminal to the negative terminal.

5.2 Charging of nickel-cadmium batteries

5.2.1 Initial charge

An initial charge should be applied after installation. Filled and charged nickel-cadmium cells require recharging to compensate for self-discharge losses during shipment and storage. Cells shipped in a discharged condition have to be given a complete charge.

The initial charge consists of the following procedures:

(a) Inspect all cells to ensure that the electrolyte level is between the high-level and the low-level lines.

(b) Follow the manufacturer’s recommendations for applying an initial charge. If the charge voltage exceeds the system voltage limit, perform the initial charge off-line from the dc system.

(c) Upon completion of the initial charge, return the charger to float voltage.

(d) At the end of 72 hours, read and record all individual cell voltages, and the electrolyte temperatures of every tenth cell for corrective action and for records.

(e) Add distilled or other approved-quality water to bring the electrolyte level of all cells up to the high level line.


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5.2.2 Float charge

(a) Float charge voltage should be maintained at 1.43 volts to 1.45 volts per cell to avoid gassing.

(b) Maintain constant voltage charging to prevent the battery from discharging at a depressed voltage level.

(c) To prevent excessive water consumption, avoid charging the battery at higher values than recommended.

5.2.3 5.2.3 Booster charge

(a) The booster charge should be 1.65 volts per cell and made monthly.

(b) A fully discharged battery in good condition can be fully charged in 4 hours.

(c) If the float charge has maintained the battery in a fully charged condition during the month, the monthly booster charge will be minimal.

(d) The booster charge should be continued until the charging current has leveled off for two consecutive readings one-half hour apart.

(e) When applying a booster charge, it is important to watch the electrolyte temperature in the cells. If the temperature reaches 43 ºC, the charging rate should be reduced at once.

6. Placing a new battery in service

6.1 Placing nickel-cadmium batteries in service. Batteries will generally be supplied “filled and discharged”, but “filled and partially charged” units can be provided. Either type should be capable of being stored for up to one year without a recharge. Vented (flooded) units can also be provided as “discharged and empty” and can be stored indefinitely. All vented batteries must be firmly fitted with vent plugs during transit. Check plugs periodically to ensure integrity of the seals. Charging during storage, charging prior to putting in service, and filling empty cells should be done in accordance with the manufacturer’s instructions and using the manufacturer’s electrolyte.


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6.2 Connections for batteries Clean all points of electrical contact to be certain of good conductivity through terminal connections. If connections are copper, apply a coat of petroleum jelly (such as Vaseline) to prevent corrosion.

7. Replacement of a battery Generally, if a battery’s capacity is less than 80 percent of the rated capacity, the recommended action (by industry consensus) is replacement. The urgency of the replacement will depend upon the available capacity margin, and the sizing criteria compared to normal load requirements. Whenever replacement is dictated, the maximum delay should be no more than 12 months.

(1) Other replacement criteria

Significant differences in the capacities of individual cells, cell polarity reversal, failure to hold charge, and inability to maintain an acceptable specific gravity are conditions which require further investigation. Replacement of individual cells may be required in order to maintain capacity.

(2) Cell replacement

Replacement cells must be compatible with the remaining battery cells and should be discharge tested before installation. As a battery installation approaches the end of its service life, it is not recommended that individual cells be replaced.


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Storage Batteries and Charger Inspection Report Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site Installation Date Rated Voltage

Plant of Manufacture Battery Charger


1. Voltage, current of battery charger in floating operation

2. Voltage, current of battery charger in boosting operation

3. Operating temperature (by touch)

4. Operating voltage of voltage sensitive relays

Charger

4. Timers and all meters operation condition


1. Float voltage at the battery terminal

2. Appearance and cleanliness of batteries and accessory

3. Battery charger output current and voltage

4. Electrolyte level

5. Cracks in cell or leakage of electrolyte

6. Corrosion at terminals, connectors, racks

7. Ventilation equipment condition

8. Visual inspection of each cell

9. Integrity of battery rack

10. Intercell connection torque

11. Condition and resistance of cable connections

Batteries

12. Capacity test

Remark




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Storage Batteries Measurement Report Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site Installation Date

Plant of Manufacture Cell Type A/Hour

Cell

No.

Cell

Voltage

Connection

Resistance

Capacity

Test

Cell

No.

Cell

Voltage

Connection

Resistance

Capacity

Test

Cell

No.

Cell

Voltage

Connection

Resistance

Capacity

Test

1 21 41

2 22 42

3 23 43

4 24 44

5 25 45

6 26 46

7 27 47

8 28 48

9 29 49

10 30 50

11 31 51

12 32 52

13 33 53

14 34 54

15 35 55

16 36 56

17 37 57

18 38 58

19 39 59

20 40 60

Remark




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VII. Battery Charger


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1. General

1.1 Description Battery charger is a rectifier unit used to change alternating to direct power for charging a storage battery. Also it is known as charger.

1.2 Types of battery chargers There are several types of rectifiers used for battery charging. All operate on the same principle permitting current to pass freely in one direction, while permitting little, if any, current to flow in the reverse direction.

1.2.1 Silicon-controlled rectifier (SCR) type

This type uses silicon diodes to provide the rectification of ac voltage input to dc voltage output. Units may include transistor-controlled magnetic amplifiers. If not filtered, units can cause electromagnetic interference (EMI) and radio frequency interference (RFI). A properly filtered unit will eliminate this problem. However, the filter capacitor may take several minutes to discharge, even after isolation of the battery charger from the ac input and the battery. This feature shall be noted by a warning label on the battery charger.

1.2.2 Controlled ferro-resonant type

This is an improved version of the simple ferro-resonant type, which was the first static battery charger developed, and which used a constant voltage transformer and selenium stacks. The simple ferro-resonant type was quieter and much easier to use than a motor-generator, but had serious control shortcomings. The controlled ferro-resonant type includes a control winding, a triac, and a control circuit to overcome these problems. It is very important for personnel to distinguish between “simple” ferro-resonant units and “controlled” ferro-resonant units to be sure that the dual-rate (float/equalize) requirement for battery charging is acceptable.

1.2.3 IGBT (Insulated Gate Bipolar Transistor) switching type

IGBT based chargers have recently emerged in the material handling market place offering


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a potential replacement to SCR and ferro-resonant counter parts in opportunity and fast charge applications. Unlike SCR and ferro-resonant chargers, IGBT chargers can switch at higher frequencies (kilo-hertz range) and provide better regulation of output voltage and current.

1.3 Rating

Number of input phases Rated output voltage (V) Rated capacity (A)

38

48

60

110

Single phase

125

10, 20, 30, 50, 75, 100, 150, 200 (A)

38

48

60

110

Three phase

125

10, 20, 30, 50, 75, 100, 150, 200 (A)

1.4 Battery charging requirement A battery cannot function without a device which maintains its properly charged condition. A well designed battery charger shall provide the correct balance between overcharging and undercharging so as not to damage a battery. Additionally, a battery charger may have features to limit or alarm when the battery discharges to the point where the cells approach exhaustion, or where the voltage falls below a useful level (usually about 80 percent of the battery’s rated capacity). Overcharging, if done frequently, results in increased water use. Overdischarging tends to raise the temperature, which may cause permanent damage.

1.4.1 Current flow

Batteries are connected to the battery charger so that the two voltages oppose each other, positive of battery to positive of battery charger and negative to negative. Battery current is the result of the voltage differences between the battery and the battery charger which flows through the battery’s extremely low opposing resistance. The voltage of the battery which


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rises during charging starts to limit current flow. Battery chargers are designed to limit charging currents to values that keep the charging equipment within a reasonable size and cost. Battery chargers must also maintain a sufficiently high current throughout charging, so that at least 95 percent of the complete storage capacity is replaced within an acceptable time period. This recharge time is usually not more than 8 hours for station service.

1.4.2 Charging equipment

Batteries must be charged by direct-current. The available sources are an ac-to-dc rectifier and an ac-to-dc motor-generator set. The use of motor-generator sets to supply station batteries is an unusual practice now because the function is so reliably and economically handled by rectifier type battery chargers. If motor generator sets are used, maintenance shall be in accordance with the manufacturer’s instructions.

1.5 Accessories for battery chargers Dependent upon the specific unit, battery chargers will be provided with various accessories. The maintenance of these devices shall be as recommended by the manufacturer. Included in the category of accessories are meters, equalizing control, indicating lamps, dc voltage level alarm, ground detection alarm, and electrolyte level alarm. Meters and indicating lamps shall be connected to the load side of the circuit breakers on the circuit being monitored. Connections on the line side can give a false indication of power availability.

1.5.1 Equalizing control

Equalizing control shall include a manual switch for transferring the lower rate float charge to the higher rate equalizing charge. Optional accessories include equalizing timers and automatically-controlled equalizing timing for adjustable interval settings.

1.5.2 Input and output

Input and output circuits are always provided with protection. Fuses are standard accessories. Circuit breakers are optional, but are a preferred means of isolating the battery charger for maintenance.


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2. Inspection

2.1 Routine Inspection


Battery chargers are designed to require a minimum of maintenance. There are no rotating parts, except in the optional timer, and all components normally have an indefinite life and no aging effects. However, it is possible for a diode or rectifying stack to fail at long intervals, either by open circuiting or short-circuiting. Therefore, it is recommended inspection of battery chargers shall be monthly inspected altogether with their battery inspection. Failed items shall be replaced in accordance with the manufacturer’s instructions.


Battery chargers shall be kept clean, dry, and checked to make sure all connections are tight. If necessary, dry air may be used to blow dust out of the interior. In the event of any irregular operation, examine and tighten, if necessary, all internal and external connections and check circuits for continuity. If the difficulty cannot be remedied, contact the manufacturer.

2.1.2.1 Checking

Regardless of the quality of the battery charger, its operation shall be checked, at the same time as its battery is inspected, to ensure that it is functioning properly. Any radical trouble will be indicated by overheated components on either the battery charger or the battery installation, by blown fuses, or by failure to complete the charge. In such cases the trouble must be located and remedied. Certain adjustments may gradually “drift” from their normal position and require correction. At each monthly inspection provide recorded checks on the following data:

(a) Check the voltage of battery chargers in floating operation.

(b) Check the current output and/or voltage of battery chargers in cycle operation, during normal se.

(c) Check the operating temperature of equipment, (by touch)


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(d) Check the operating voltage of voltage sensitive relays.

(e) Check the operation of timers.

(f) Check that all meters are at zero calibration.

2.1.2.2 Slope characteristic

In the event of any apparent improper operation, the battery charger slope characteristics shall be checked. Every battery charger has a relationship between the output voltage and the output current throughout its complete range. For any given voltage, the battery charger will always deliver a given current and vice versa. This slope characteristic is inherent in the battery charger and is not affected by the size or type of battery. If actual readings of voltage and current fall on or reasonably near the slope line, the battery charger is not at fault and the trouble is elsewhere.


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VIII. Protective Relays


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1. General

1.1 Description A relay is an electric device designed to interpret input data. When specific input conditions occur, the relay responds to cause contact operation or a similar sudden change in associated electric control circuits.

These sections describe electric power apparatus relays and relay systems which are designed to operate circuit breakers and contactors, usually medium-voltage units. Relays can be set more precisely than fuses. Relays are adjustable with respect to both time and current, a feature that also applies to solid-state, direct-tripping, low-voltage circuit breakers.

Input data analyzed is usually electrical, but may be mechanical or thermal, or evaluate other conditions or a combination of conditions. Electrical conditions can be overcurrent, overvoltage or undervoltage, a combination of current and voltage, current balance, direction of current flow, frequency, impedance, or other electrical data.

1.2 Type of relay All relays operate in response to one or more electrical or physical quantities to open or close contacts or trigger power electronic devices, such as thyristors. Relays will generally be of the electromechanical or solid-state type.

1.2.1 Electromechanical relays

These relays have been used for years and provide simplicity, reliability, security, low-maintenance, and long life. Basic units are constructed to respond instantaneously or with a time-delay to the actuating quantity.

1.2.1.1 Instantaneous units

Instantaneous units act on an electromagnetic attraction operating principle wherein a plunger, solenoid, hinged armature, or balance-beam is pulled into a coil or pole face of an electromagnet. They can be used in both ac and dc power systems.

1.2.1.2 Time-delay units


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Time-delay units act on an electromagnetic induction operating principle, whereby torque is developed in a movable rotor (disc or cup) which rotates between two faces of an electromagnet. These units can only be used in ac circuits. Time overcurrent and time under/overvoltage relays are generally of the disc design type, while high-speed overcurrent, directional, differential, and distance relays are more often of the cup (cylinder) design type.

1.2.2 Solid-state relays

Solid-state relays are extremely fast in their operation, as they have no moving parts. Other advantages are lower burden, high seismic-withstand, and reduced panel space. Many are programmable, allowing increased choices of time-current characteristics.

Solid-state relays shall be used for protective relay of distribution system in correspondence to GECOL specification standard. Solid-state relays require no preventive maintenance, but they do require a periodic maintenance check.

2. Delivery and storage Relay products require careful handling before installation on site. Examine the delivered products to ensure that they have been damaged during transport. If a product has been damaged, a claim shall be made to the transport contractor and the local representative of manufacture shall be promptly notified. And the device contains components which are sensitive to electrostatic discharge. Unnecessary touching of electronic components must therefore be avoided.

To store relay products safely, keep containers tightly closed in a cool, well-ventilated place.

3. Inspection and test

3.1 Field inspection before operation

3.1.1 New installations (Initial inspection)

Before placing a new installation into operation, polarity of instrument transformers and the wiring to the relays shall be checked. In some cases, the manufacturer's polarity marking has been found to be incorrect. New relays shall be inspected carefully and all blocking put in by the manufacturer removed. The test man shall read instruction books furnished by the


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manufacturer to become familiar with construction and operating principle of the relays.

3.1.2 Initial operations

A sufficient number of initial operations shall be made by manually operating relay contacts to make sure that all devices which shall be operated by the relay, function freely and properly, including auxiliary contacts and targets within the relay. Breaker trip coils and other devices operated by the relay shall be checked to see that proper operation is obtained at voltages considerably below normal (approximately 56 percent of normal voltage for breaker trip coils). The voltage drop in trip circuits and tripping current required shall be checked. Factory adjustments on relays, other than taps, or other adjusting devices intended for customary adjustment shall not be changed unless tests show that factory adjustments have been disturbed, in which case the manufacturers' instruction books shall be followed.

3.2 Inspection and test for solid-state relays

3.2.1 Daily inspection

Daily inspection of protective relay shall be performed at the same period of patrol in correspondent to patrol procedure regarding circumstance condition, each relay condition (operation position, movement, smell, damage, etc.), switches position, and visual inspection.

3.2.2 Routine inspection and test

3.2.2.1 Interval of Inspection

It is recommended that protective and auxiliary relays be given a complete calibration test and inspection at least once a year. Testing may be necessary after a relay operation. Visual inspections of the target shall be made any time other area visual inspections are required. Relay settings shall be checked at least once a year and after any incorrect operation or redesign of the system. These inspections, supplemented by suitable tests, shall be thorough enough to detect any faulty relays, settings, or wiring errors before trouble is encountered.

3.2.2.2 Test considerations

(a) Relays shall be completely disconnected from any live circuit when they are


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inspected or tested. Only specially trained electricians shall be permitted to repair and adjust relays. The manufacturer’s instructions shall be checked for the proper procedures.

(b) Before starting to test any relay on equipment in service, the test man shall become familiar with the relays and the circuits involved. Where test blocks are used, the test man must make sure that in removing or inserting plugs that a current transformer circuit will not be opened, resulting in a voltage being built up which may be dangerous to personnel, property, or equipment, or cause an important circuit to trip out. In old installations where test blocks are not available, current transformer circuits must be short circuited by jumpers having reliable clamping devices which will not come loose, before the relay current circuit is opened.

(c) Tests shall simulate normal operating conditions. Avoid overtesting because such tests can often cause more problems than they correct. Consider the variables that can cause problems, such as relay complexity, environment, and history. Other considerations are relay age and relay stress (relays operated at greater currents and/or control voltages because of station expansions).

3.2.2.3 Test tools and devices

A good set of testing equipment and relay tools are important. The test equipment for field testing must be portable, so tests can be made at the relay panel. For most of the common relays, the following will be needed: a variable voltage autotransformer, a multi-range ac and dc voltmeter, a multi-range ac and dc ammeter, an ohmmeter, auxiliary current transformers, a timer, a three phase shifter, and auxiliary relays. Test plugs, leads, non-inductive resistors, and a relay tool kit will also be required. In general, most laboratory test equipment is portable and can be used in the field. Test instruments are available in prepackaged test sets. The use of these sets simplifies testing.

3.2.2.4 Inspection and test method

(1) Visual inspection

All relays shall be given an annual routine inspection. This inspection shall include the following:

A visual inspection shall be made of all relays on a terminal including the tripping


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auxiliaries and accessories. Any drawout type relay shall be withdrawn from its case for a closeup examination. All other, including auxiliaries, shall at least have covers removed. Included in this visual inspection shall be a check for loose connections, broken studs, burned insulation, and dirty contacts.

(a) Keep equipment clean by periodic vacuuming or blowing out of dirt, dust, and other surface contaminants.

(b) Keep the equipment dry and protected against moisture and corrosion.

(c) Inspect to see that all connections, leads, and contacts are tight and free as possible from effects of vibration.

(d) Check to see that there is adequate ventilation to conduct heat away efficiently.

(e) Preventive measures shall not be applied unnecessarily as this may contribute to failures. For example, printed circuit cards shall not be pulled from their racks to be inspected if there is no real need. Operating test switches unnecessarily may introduce damaging voltage transients.

(2) Performance test

Static relays shall be annually tested in accordance with manufacturer's recommendations given in relay instruction books. As there are no moving parts in static relays, there is no physical wear due to usage and no need for lubricants.

A test trip shall be made of all relay systems. All relay elements which initiate some protective function shall be checked. This includes reclosing, carrier starting, or any similar type function. After proving that tripping relays will successfully trip the circuit breaker and that all reclosing schemes work, continuity checks shall be used, where applicable, to complete the checkout of the circuit breaker trip circuits.

4. General requirements for test

4.1 Circuit burden measurements for CTs When CT circuits are modified such as by addition of relays, meters, or auxiliary CT's, measurements shall be taken to determine the burden of the overall CT secondary circuit. These measurements shall normally be on a phase-to-neutral basis. When auxiliary CT's are


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involved, additional and separate measurements shall be taken on the secondary circuit of the auxiliary CT's.

4.2 Grounding CT and PT circuits The CT and PT circuits shall be grounded at only one point. Relay misoperations can be caused by grounding the neutral at two points, such as one ground at the switchyard and another at the relay panel. At least once every 3 years with the primary de-energized, the known ground shall be removed and the overall circuits shall be checked for additional grounds and insulation breakdowns.

4.3 Open-secondary circuits Secondary circuits of CT's must not be open while primary current flows.

Extreme care shall be taken to avoid breaking the secondary circuit while primary current is flowing. If the secondary is open-circuited the primary current raises core flux density to saturation and induces a high voltage in the secondary which can endanger human life, and can damage connected apparatus and leads. If it is necessary to change secondary conditions while primary current is flowing, the secondary terminals must be short-circuited while the change is being made. Caution shall be exercised when working with differential circuits as shorting a current transformer in an energized differential relaying circuit could result in a relay operation. It is recommended that the secondaries of all current transformers be kept short-circuited at all times when not installed in a circuit such as being held in stock or being transported.

5. Test records A complete record shall be kept of all test data and observations made during tests and inspections, including identifying numbers of test equipment used. The following relay test reports are available at maintenance department and one copy of each is included:

(1) Overcurrent and earth fault relay test report

(2) Differential relay test report

(3) Distance relay test report


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IX. Grounding Inspection


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1. General

1.1 Description The term grounding implies an intentional electrical connection to a reference conducting body, which may be earth (hence the term ground), but more generally consists of a specific array of interconnected electrical conductors. The resulting circuit is often referred to by several terms, such as: ground plane, ground grid, mat or ground system. Grounding systems shall be serviced as needed to ensure continued compliance with electrical and safety codes, and to maintain overall reliability of the facility electrical system. Action must be initiated and continued to remove, or reduce to a minimum, the causes of recurrent problem areas. When possible, maintenance inspections shall be performed at times which have the least affect on user activities.

1.2 Purpose of grounding Adequate grounding is essential to the protection of life and equipment. Reasons for grounding include:

(1) Safety for the public

Any metallic equipment that could expose the public to a source of dangerous potential must be grounded.

(2) Safety for utility worker

Any part that does not normally carry current shall be considered energized until it is grounded.

(3) Equipment and personnel protection

Grounds help stabilize circuit voltages and provide a path for ground faults so that protective devices will operate. Grounds help limit system overvoltage and neutral imbalance problems. Grounds provide a path for surges, which helps eliminate equipment insulation failures.

1.3 Safety precautions while making ground tests


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1.3.1 Station ground tests

It shall be strongly impressed on all test personnel that a lethal potential can exist between the station ground and a remote ground if a power-system fault involving the station ground occurs while ground tests are being made. Since one of the objectives of tests on a station-ground system is to establish the location of remote earth for both current and potential electrodes, the leads to these electrodes must be treated as though a possible potential could exist between test leads and any point on the station ground grid. Some idea of the magnitude of this possible potential may be gained from the consideration that even in the larger stations the ground grid shall have impedance in the order of 0.05 W to 0.5W. Assuming for this example that the ground-fault current through the grid is in the order of 20 kA the potential to remote earth (ground potential rise) will be in the order of 1.0 kV to 10 kV. For higher ground impedance or greater fault currents, the rise of station-ground voltage may exceed 10 kV. The preceding discussion points to the necessity of caution when handling the test leads, and under no circumstances shall the two hands or other parts of the body be allowed to complete the circuit between points of possible high potential difference. It is true that the chances are remote that a station-ground fault will occur while test leads are being handled, but this possibility shall not be discounted and therefore the use of insulating shoes, gloves, blankets, and other protection devices are recommended whenever measurements are carried out at an energized power station. In all cases, safety procedures and practices adopted by the particular organization involved shall be followed.

1.3.2 Surge arrester ground tests

These grounds fall in a special category because of the extremely high short-duration lightning currents carried by surge-arrester grounds. These currents may be in excess of 50 000 A for surge currents, with a possibility of fault system currents in the case of a defective surge arrester. An isolated surge arrester ground shall never be disconnected to be measured, since the base of the arrester can be elevated to the line potential. A surge-arrester ground can be tested as long as precautions axe taken to minimize arrester discharge.

1.3.3 Small isolated ground tests

Another precaution concerns possible high-potential gradients around the current electrode. If current is passed into a remotely located electrode, as in the fall-of-potential method, it is worthwhile to ensure against a curious person being allowed near the current electrode while tests are in progress. Similarly, in rural areas grazing animals shall not be allowed near the test current electrode.


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1.4 Standard of grounding resistance

Voltage Level (kV) Distribution facilities

66 30 11 0.4 Remarks

Overhead ground wire 30Ω 50Ω - - Every pole

Surge arrester for feeders 20Ω 20Ω 20Ω -

Outer metallic parts of devices 10Ω 10Ω 10Ω 100Ω

Cable connection parts 10Ω1) 10Ω1) 10Ω2) -

Legs of steel tower 30Ω 30Ω - -

Steel post - - 10Ω -

Overhead transformer - 10Ω 25Ω -

Underground transformer 5Ω 10Ω 10Ω -

Installation of a reactor for 66kV &

30kV

Surge arrester for transformers 5Ω 15Ω 15Ω

The neutral line of the last pole of low voltage lines - - - 100Ω Every branch line

NOTE: 1) 30kV and 66kV cable connection parts should be earthed by cross bonding type.

2) 11kV cable connection parts should be earthed by solid ground type on both ends.

2. Inspection

2.1 Inspection after installation

(1) After completion of installing a counterpoise, perform the measurement of normal

ground resistance and transient ground resistance, considering the follows described below.

(a) Ground resistance varies according to the water content of a stratum. Therefore, conduct the measurement of the grounding resistance for the period when the grounding resistance value is high as sunny days continue.

(b) In spite of installing an auxiliary electrode well, the grounding condition of electrode is bad and the sensibility of a galvanometer is poor, perform the measurement after making contact condition good by pouring some saltwater around the electrode.


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(c) Be careful of voltage from the ground resistance meter, which is very high.

(2) The grounding shall be constructed according to the design and construction standard for

ground.

(3) In case of exceeding the basic grounding resistance value, the auxiliary grounding shall be made and ground resistance lowered using the chemical for reducing earth resistivity.



Voltage level Inspected objects Inspection interval

Overhead line 1 time per 3 years

Underground line When needed 66, 30kV

66 kV main substation Sampling check every 5 years

11kV Overhead and underground line, substations 1 time per 2 years


(1) Check the connection condition of grounding connection parts.

(2) Measure the ground resistance of grounding wire and ground grid.

3. Testing method The methods of measuring ground resistance shall be divided into two cases that a grounding wire is not connected to system neutral and connected to system neutral. When a grounding wire is not connected to system neutral a battery type ground resistance tester using auxiliary electrodes shall be used and when the grounding wire is connected to system neutral on the energized line, a Hook-On Earth Tester shall be used for measurement.

3.1 When grounding wire is not connected to neutral


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3.1.1 Direct method

This methods requires the least time but shall be used only when the resistance of the system neutral is known. This method is best used on stations that have not yet been energized, as it allows for easy removal of the system neutral.

Figure 11 Direct method for ground resistance test

(a) Disconnect the ground grid from the system neutral.

(b) Connect the ground resistance meter as shown in Figure 11.

(c) Take the resistance reading.

(d) Calculate the ground grid resistance from the below formula:

R2=X-R1 where

X is the reading from the meter

R1 is the known system neutral resistance

R2 is the ground grid resistance

(e) Record R2 on the Substation Ground test Data sheet.

(f) Reverse the meter connections so P1 and C1 are connected to the grid, and P2 and C2 are connected to the neutral. Repeat steps (c), (d) and (e). Resistance readings shall be approximately the same.

3.1.2 Two prove method

This method requires more labor time and must be used when the resistance of the system neutral is unknown.

Grid (R2) Neutral (R1)

X=R1+R2

Total (x)

P1 C1 P2 C2


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Figure 12 Probe placement for measuring ground resistance of station grid

(a) Install the remote current C2 and potential P2 probes as shown in Figure 12. The remote probes consist of 3 to 4 interconnected ground rods spaced 1.5 m apart.

(b) Record all test information and a drawing of the test layout on the substation ground test data sheet.

(c) Use a multi-meter to measure the residual DC and AC voltages between each remote probe and the station grid.

(d) Connect meter terminals P1 and C1 to the ground grid. Connect the C2 probe lead to meter terminals P2 and C2. Take the reading.

(e) Repeat step (d) with the P2 probe lead connected to meter terminals P2 and C2. If either reading is above 500 ohms, reduce the probe resistance by pouring saltwater around the remote probes or by installing more ground rods.

(f) Connect terminal P2 to the remote potential probe, and C2 to the remote current probe. Leave terminals P1 and C1 connected to the ground grid.

(g) Read the apparent resistance between the station grid and remote earth.

(h) Exchange the P2 and C2 test lead connections at the meter and repeat (f)-(g). Readings must be in agreement for a proper test.

Station grid Angle must be greater than 90º

Remote current Probe C2

Remote current Probe C2

1..5 m or More 1..5 m or More


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Figure 13 Example of using a battery type ground resistance tester for ground

resistance measurement

3.2 When a grounding wire is connected to system neutral

3.2.1 Method of using a Hook-On Earth Tester

(1) Ready before using Hook-On Earth Tester

(a) Check batteries inside a used Hook-On Earth Tester. Replace the batteries if LOW signal is shown on the tester’s display when selecting “A” or “Ω” out of the ranges of function selection switch

(b) Remove a contaminant on contact part of the clamp CT clearly.

(c) Check the error using a resistance ring before measurement.

(2) Measuring the ground resistance

(a) Grip the clamp CT to a ground wire to be tested.

(b) Select “Ω” out of the ranges of function selection switch.

(c) Take reading, pushing hold switch in the condition that reading is not flickering when the ground resistance is shown on the LCD.


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Figure 14 Example of using a Hook-On Earth Tester

4. Reducing ground resistance

4.1 Methods of getting optimum ground resistance

(1) Using a number of electrode

It is possible to get minimum ground resistance by laying a number of electrodes with the most effective spacing.

(2) Using a long earth bar

It is effective to use long earth bar at the place where ground resistance is lower than where to reach by using earth bar with standard length. In general, ground resistance became rapidly low when earth bar contacts with soil with low ground resistance in laying it.

(3) Using a chemical for reducing earth resistivity

It makes ground resistance lower effectively to use high intensity chemical for reducing earth resistivity including carbonic acid materials, cements, special additives, etc at the ground with high resistance.

(4) Using together with methods described above

In order to easily lower the ground resistance to targeted level, it is necessary to use together with more than two of methods described above.

4.2 Constructing a chemical for reducing earth resistivity


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(a) Mix a chemical for reducing earth resistivity and water in a bottle. At the moment, refer the instruction book because the mixture rate of a chemical for reducing earth resistivity and water depends on products.

NOTE: Generally a high intensity chemical for reducing earth resistivity is constructed mixing water 4~6L per 10kg or in case of earthon, water 10~20L per 5kg.

(b) Refill up after applying electrodes or grounding wires so as to wrap enough using mixed chemical for reducing earth resistivity.

NOTE 1: when it is hard to use water because of surrounding conditions such as mountains, refill up after applying a pulverulent body on the electrodes or grounding wires directly.

NOTE 2: It will be enough that each 10kg of chemical for reducing earth resistivity is used to at the area of about 0.5 to 1m3.


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Substation Ground Test Data (Direct Method)

Page: of Substation: Weather: , ºC Date: . . .

Test No. Location of C1, P1 Location of C2, P2 Ohms(X)

1 Grid Neutral

2 Neutral Grid

Test Instrument used System Neutral Resistance (R1)

Ground Grid Resistance (R2=X-R1)

Remark

Foreman : Office / Section supervisor :


Date : Date :


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Substation Ground Test Data (Two-Probe Method)

Page: of

Substation: Weather: , ºC Date: 200 . .

Grid isolated from system neutral Test No.

Location of P2

Probe

Location of C2

Probe Ohms

Yes No

1

2

3

4

Test Instruments Used: Earth Resistance meter Resistance of Ground Mat in Ohms :

Ground Mat Connections tested satisfactorily:

Probe Mat Distance to

Probe Location

Prob to Mat

Voltage AC

Probe to Mat

Voltage DC Probe Resistance

Number of

Ground Rods

A m Ohms

B m Ohms

External Grounds Tied to Substation Mat



Date : Date :


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Distribution Ground Resistance Test Data

Page: of

Weather: , ºC Date: 200 . . .

Test result Grid isolated from system neutralNo.

Equipment

or Device Location

Tested

Ohms OK Not OK Yes No

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Remark



Date : Date :


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X. Pole


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1. General

1.1 Description Pole is main stuff among supporters and materials on the overhead distribution line. Its kinds are wood pole, concrete pole, metal pole. Pole is mainly used on the 30kV or less distribution line.

1.2 Type of poles

1.2.1 Concrete pole

Reinforced concrete poles have a projected life of 60 to 80 years and should require no attention, except for replacement when damaged.

Concrete poles are preferred under conditions where the life of wood poles would be unduly shortened by decay or pests. When hauling concrete poles, they must be secured so they cannot bounce.

Hard bouncing in transit will crack or chip the poles, especially when traveling over rough ground, roads, or railroad tracks. Concrete poles also require special attention if field drilling is required or there is a need for special banding or other attachment methods. Poles setting depths may in some cases be the same as wood poles, when the pole has been designed to be the equivalent of a wood pole of the same class and length. Engineering personnel should evaluate pole setting depths, guying, and foundation requirements.

1.2.2 Wood pole

The average life span of a full-length pressure-treated wood pole can be maintained and even extended another 10 to 20 years with a proper inspection, treatment, and reinforcement program.

1.3 Characteristics of poles


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Table 16 Characteristics of poles

Concrete poles Wood poles

Diameter (mm)

Diameter at top (mm) Class

Nominal length

(m)

Tip Butt

Normal Burial Depth Line Min. Max.

Diameter at 1.5m from butt end (mm)

Normal Burial Depth Line

9 140 275 1,500 125 150 180 1,500

10 140 290 1,700 125 160 185 1,700

11 140 305 1,800 125 160 195 1,800 Light

13 - - - 130 170 210 2,200

9 190 325 1,500 150 180 220 1,500

10 190 340 1,700 150 185 230 1,700

11 190 355 1,800 150 190 240 1,800

13 - - - 160 200 260 2,200

Medium

16 - - - 170 215 305 2,700

9 270 405 1,500 190 240 275 1,500

10 270 420 1,700 190 245 285 1,700

11 270 435 1,800 190 250 295 1,800

12 270 450 2,000 - - - -

13 270 465 2,200 195 255 320 2,200

14 270 480 2,200 - - - -

15 270 495 2,500 - - - -

Stout

16 270 510 2,700 200 265 365 2,700

1.4 Consideration

1.4.1 Pole foundations

Other than for poles, the use of concrete in pole-line structures is limited almost entirely to the foundations. Where used for metal structures, the foundation may often be reinforced and extend above ground. Any small cracks should be filled with a high-strength grout. If


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substantial damage is found on existing foundations, remove loose concrete, clean surfaces, and restore the foundation to its original size. For wood and concrete pole-line structures, the backfill may be of concrete to provide better bearing in soft soils, and may or may not be visible at the surface. No maintenance is required.

1.4.2 Pole platforms

Platforms supported by one or more poles are used to mount transformers, regulators, or other heavy equipment above-ground. They are usually built with wooden stringers and flooring, or with wood flooring on steel beams. Many platforms now in use are composed of untreated timbers; these should be treated with suitable preservative to extend their useful life. When replacement is necessary, use fully treated timbers or consider installing ground mounted equipment.

2. Handling and storage

2.1 Concrete pole

2.1.1 Storage

(a) Store on dunnage placed 1/5 of the total length from each end. Location of temporary support points may vary from this rule for both storage and handling. Dunnage is ideally made from 4 x 4 fir, pine, or similar wood which is finished enough to have opposite sides flat and parallel (no logs or branches). The dunnage should be in one piece for the full width of the stack and be of sufficient thickness as to allow the placing of slings or the insertion of forklift fingers between the layers of poles. Weathered lumber is better than newly-cut because the latter may stain the concrete when moisture is present.

(b) Store on a level surface (if surface is not paved, be certain the ground is solid enough so that the dunnage does not sink into it).

(c) When poles are stored in more than one layer, each piece of dunnage must be placed one above the other, so that the weight of the poles above is transmitted directly downward through the dunnage and does not induce bending stresses in the poles.

(d) Distribution poles should be stacked no higher than nine layers and smaller poles no higher than twelve layers.


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(e) Each succeeding layer of poles should be placed with the tips in the opposite direction of the layer below.

(f) Poles should be aligned so that the tips in each layer form a straight line normal to the center line of the poles.

(g) Place wedges on the dunnage next to the poles to prevent their rolling.

(h) Do not step on the cantilevered tips of small poles in storage. Handle poles with reasonable care so as to avoid dropping or otherwise striking them against each other or other hard, solid objects.

2.1.2 Handling

(a) In lifting the pole from a single pick-up point, use either a choker sling or a loop sling with one complete extra turn around the pole just above the balance point.

(b) When lifting the pole using two pick-up points from a single hook, a choker-type attachment should be used on the pole.

(c) Poles with a polished or textured surface should be handled with a nylon or other non-metallic sling. For these poles, fingers of a forklift should be fitted with protective covers.

(d) When using a forklift to handle poles, always use softeners on the fork tines. Also, always use wedges to prevent poles from rolling.

2.2 Wood pole Poles treated with oil borne preservatives should be installed soon after treating to minimize lateral movement of preservative to the extent that subsequent durability of the treated product will be reduced. This is a particularly important consideration in procurement programs for poles that might normally be expected to be in storage for a minimum of one year.

Poles treated with creosote or oil base preservatives stored in a horizontal position for over 18 months can lose preservative due to bleeding and volatilization or the preservative can migrate in the wood. To minimize this loss, poles should be rotated periodically while in storage.

Migration or loss of preservative during storage is not a problem with water-borne


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preservatives.

Figure 15 Incorrect Storage

Figure 16 Incorrect Storage

Figure 17 Correct Storage

Figure 18 Handling by crane


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3. Inspection

3.1 Concrete pole inspection


Inspection of concrete poles shall be performed at the same period of patrol time.

3.1.2 Inspection methods

(1) Examine the general physical and installation condition of the pole for deficiencies such as:

(a) Broken

(b) Visible cracks which penetrate through the pole shell thickness.

(c) Leaning or badly leaning pole

(d) Mechanical damage

(e) Horizontal cracks

(f) Loose foundation

(g) Missing or unreasonable pole tags (pole number)

(2) Take note of the condition of the immediate area around the pole such as:

(a) Hazardous (pole installed on the road, prone to mechanical damage, etc)

(b) Inside house or private property

(c) Installed at or very rice field or grassy area or near creek

3.2 Wood pole inspection


Inspection of wood poles shall be performed at the same period of patrol time. But sounding inspection and boring test of wood poles will be performed only when the condition of a


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wood pole is needed to be inspected in more detail in the process of inspection.


3.1.2.1 Visual inspection

Visually inspect the exposed portion of the wood pole from groundline to the top.

(1) Examine the pole for signs of degradation such as:

(a) External decay (shell rot, exposed decay pockets)

(b) Insect infestation (beetle exit holes, termite tunnels)

(c) Bird nest at the pole top

(2) Examine the general physical and installation condition of the pole for deficiencies such as:

(a) Broken

(b) Pole split

(c) Burned top

(d) Bad pole checks (checks exposing untreated heartwood)

(e) Leaning or badly leaning pole

(f) Mechanical damage

(g) Horizontal cracks

(h) Loose foundation

(i) Missing or unreadable pole tags (pole number)

(j) Holes left by removed bolts and other fasteners

(3) Take note of the condition of the immediate area around the pole such as:

(a) Hazardous (pole installed on the road, prone to mechanical damage, etc.)

(b) Inside house or private property


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(c) Presence of the termite mounds

(d) Installed at or very rice field or grassy area or near creek

3.1.2.2 Sounding inspection

Perform sounding inspection as follows:

(1) Using a hammer, pound the pole in a spiral direction around it, starting from groundline near the widest check and reaching up to the point of secondary attachment.

Notes:

(a) A properly sounded pole bears hammer marks. Special effort should be made to determine the soundness of the pole at groundline.

(b) A sharp ring (or solid sound) indicates “good” pole.

(c) A hollow sound (like a drum) or a dull thud indicates rot.

(2) Repeat pounding the pole, but this time in a downward direction, until the entire circumference has been sounded.

3.1.2.3 Boring test

(1) Bore pole with a sharp increment borer which extracts a core approximately 5 mm in diameter.

(a) Bore pole toward the center of the pole by using the increment borer, applying steady pressure to start, and in as nearly a horizontal line as possible.

(b) When boring below the ground line, the pole surface at the spot bored should be thoroughly cleaned of soil and grit by shaving or brushing.


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Figure 19 Increment borer and its use

(2) Plug all bored holes by hammering in a tight-fitting treated wood plug as shown in figure

19, regardless of whether the pole needs to be replaced.

(a) Habitually and promptly drive a plug in each hole before boring another or before proceeding with other work. Otherwise, a bored hole may be overlooked, opening the way for future internal decay.

(b) The plugs, made of doweling, may be obtained from most pole suppliers.

Those pointed on one end are preferable but not required. They should be 80 to 100 mm long with a diameter 0.8 mm larger than the hole bored to provide a snug fit.

(c) The borer, an adequate supply of plugs, and a hammer should be kept together as a kit.


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Figure 20 Sealing a test hole with a treated wooden plug

(3) Evaluate the extracted core from borings test

(a) The extracted core should be carefully examined for wood integrity or evidence of decay, extent of any decay pocket, and the amount of original preservative in the wood.

(b) Decay will be evidenced by crumbly wood in part of the core. If a pole is badly decayed, a core may not be withdrawn intact. Borings may sometimes be soft and moist, but not decayed, if preservative is present and the wood fibers are strong.

Figure 21 Cores extracted with an increment borer

4. Wood pole reinforcement Pole reinforcement technology has developed several methods of pole repair which can


- 144 -GECOL

restore poles to their original groundline strength. Engineering personnel should evaluate the selected method to ensure that the proposed installation is adequate.

4.1 Stub pole A length of pole of the same size as the existing pole, and long enough to extend from the butt of the pole to about 1.5 meters above the ground line, is set flush alongside the existing pole. Follow criteria for setting a new pole and band it to the existing pole at the top and about 400 millimeters above the ground line.


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Figure 22 Wood stub pole

4.2 Steel reinforcing If several poles need reinforcing, steel reinforcing may be more economical than the use of stub poles. The steel reinforcement consists of a “C” shaped galvanized steel section (as shown in figure 23, which is pneumatically driven to below the pole butt and then strapped to the existing pole. The equipment for driving the reinforcing is specifically designed for the purpose, but its use will be more economical than digging holes for several stub poles. Although the steel reinforcing can be installed by in-house forces, it would probably be advantageous to have this work done by a firm specializing in this service. Steel reinforcing also provides extra protection from vehicles in congested areas. Engineering is required to ensure proper installation since the overall strength of the steel truss and pole combination depends on the strength of the banding system.

Wrap with two layers of 1360 kg guy strand use (26 to 30m) of strand

Stubbing Strand washer

20º

1.52

to 1

.6 m

1.32

to 1

.47

m

1.52

to 1

.6 m

0.

2 m

Wire clamp

Staple

Tension strand with Double arming bolt

(cut off after installation)

Direction of lead


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Figure 23 Steel reinforcing for a wood pole

4.3 Compound set methods There are a number of compound set methods. Engineering evaluation should select the appropriate method.

(1) Compound

The simplest method requires a compound (mixed in a completely self-contained mixing unit) which fills a hole slightly larger than the pole diameter. It is suitable also for straightening poles.

Seals

Band

Band

“C” shaped steel truss

Band

Treating Hole

Decay

1.2m

254 mm

381 mm

Ground Line


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(2) Compound and casing

The decaying region is first treated with a liquid fumigant. A split-metal casing is driven below grade by rotary-driven equipment. The casing is filled with an epoxy-aggregate for stabilization and extra strength. The filler may also contain an approved preservative additive that migrates to the outside surfaces of the pole under a time-delay release action.

(3) Compound, rebars, and collar

This method requires a 0.6-meter deep trench to be excavated around the pole and several 1.2-meter long rebars to be stapled about the pole. An inert 0.9 to 1.2 meter collar descends to about 0.6 meters below the ground line and is filled by funnel with hand or electric mixed epoxy-resin compound. Periodic tamping is needed to ensure proper compound setting. The trench is then backfilled after the compound has cured.

5. Recommendations The following recommendations are general in nature. The actual and final recommendations essentially rest the sound judgment of the inspector.

5.1 Concrete pole inspection results

Findings Recommendations

Broken Replacement

Visible cracks which penetrate through the pole shell thickness

Replacement

Mechanical damage Minor Repair Severe Replacement

Horizontal cracks Replacement Loose foundation Reinforcement with readable correct pole tag Pole tag Unreadable or wrong Replacement with readable correct pole tag

Missing pole tag Installation of correct pole tag Installed in hazardous locations or inside house or private property

Relocation


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Installed near creek Relocation or reinforcement of pole foundation (if still needed)

5.2 Wood pole inspection results When a pole is recommended for technical evaluation or treatment, it shall mean that the pole shall be evaluated or treated in accordance with procedures manual.

5.2.1 Visual inspection results

Findings Recommendations

Signs of decay

Early stage of decay Technical evaluation Extensive decay (rotten) Immediate replacement

Insect infestation Early stage of infestation Further inspection using; adder/bucket truck Extensive termite infestation Immediate replacement

Bird nest on pole top Further inspection using ladder/bucket truck Broken Immediated replacement Pole split

Split running through bolts holding the crossarm or top insulator

Replacement

Split 90° to the bolts or is minor Usually no replacement needed. Use good judgment

Burned top Use good judgment Bad pole checks Treatment Leaning pole Mechanical damage

Exposing untreated portion of pole Treatment Severe Replacement

Compression breaks or horizontal cracks Replacement Loose foundation Reinforcement of pole or pole foundation Pole tags

Unreadable or wrong Replacement with readable correct pole tag Missing pole tag Installation of correct pole tag

Installed in hazardous locations or Relocation


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inside house or private property

Installed in areas with termite mounds or installed at or very near rice fields or grassy areas

Replacement with concrete pole

Installed near creek Relocation or reinforcement of pole foundation (if still needed)

Holes left by removed bolts and other fasteners

Treatment of and plugging with treated wood plug or dowels all holes

5.2.2 Sounding inspection results

Finding Recommendations

Sharp ring sound (“good” pole) Retreatment, if scheduled for retreatment

Hollow or dull thud sound (rotten pole) Replacement Neither sharp nor hollow sound For technical evaluation Suspicious portion beyond reach of inspector For reinspection using ladder/bucket truck

Guideline for inspection of materials

- 150 -

Distribution Pole Inspection Report No.

Pole Identification Visual Inspection Above Ground Inspection of

Pole vicinity

Sounding

Inspection

Pole

No.

Pole

Location

Pole

Typ

e

Year

inst

alle

d/la

st tr

eate

d

Exte

rnal

dec

ay

Inse

ct In

fest

atio

n

Bird

nes

t on

the

pole

top

Bro

ken

Pole

split

Bur

ned

Top

Bad

pol

e ch

ecks

Lean

ig p

ole

Mec

h. d

amag

e

Com

pres

sion

bre

aks

Hor

izon

tal c

rack

s

Loos

e fo

unda

tion

Mis

sing

tag

Unr

eada

ble/

wro

ng ta

g

Bol

t hol

es (w

ood

pole

)

Cra

cks t

hru

shel

l(con

c)

Haz

ardo

us lo

catio

n

Insi

de h

ouse

/priv

.pty

With

term

ite m

ound

s

Ric

e fie

ld/g

rass

y ar

ea

Nea

r cre

ek

Solid

soun

d (G

ood)

How

llow

soun

d (r

otte

n)

Susp

icio

us

Recommendation/

Remark

Foreman: Office/Section supervisor: Signature: Signature: Date: . . . Date: . . .


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XI. Insulator


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1. General

1.1 Description of insulator The function of an insulator is to support a conductor or conducting device safely. An insulator, being of a nonconductive material, physically and electrically separates the supported item from any grounded or energized conductors or devices.

1.2 Types of insulator

1.2.1 Porcelain insulator

Porcelain insulators are manufactured from special clays to produce a plastic-like compound which is molded, oven dried, dipped in a colored glazing solution, and fired in a kiln. The glossy surface of the glaze makes the insulator surface self-cleaning. Large porcelain insulators are made up of several shapes cemented together. A chemical reaction on the metal parts from improper cementing can result in a cement growth which can be sufficiently stressful to crack the porcelain.

Suspension porcelain insulator Pin Porcelain Insulators

Figure 24 Types of porcelain insulator

1.2.2 Glass insulator

Glass insulators are made from a mixture of sand, soda ash, and lime which is mixed and


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melted in an oven, then molded, cooled, and annealed.

Figure 25 Suspension glass insulator

1.2.3 Composite (Polymer) insulator

Recently, some electric utilities have begun converting to composite for some types of insulators which consist of a central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or EPDM. Composite insulators are less costly, lighter weight, and they have excellent hydrophobic capability. This combination makes them ideal for service in polluted areas. However, these materials do not yet have the long-term proven service life of glass and porcelain.

Figure 26 Polymer insulator


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2. Deliver and storage (a) When handling insulators, care must be taken to be sure that rigging is applied

properly to prevent damage to the insulator and/or to adjacent equipment and personnel.

(b) Cracked or chipped porcelain or glass produce sharp edges which can result in severe cuts on the hands and arms of personnel working around them.

3. Inspection Insulator assemblies are used in overhead power transmission and distribution lines to mechanically support high-voltage conductors while providing adequate insulation to withstand switching and lightning over-voltages. Since the useful life in service of the individual insulator elements making up these strings are hard to predict, they must be verified periodically to insure that adequate line reliability is maintained at all times. Over the years many testing methods have been used for this purpose, each one with its own advantages and disadvantages.

3.1 Interval of detection

3.1.1 Insulators on the 66kV or 30kV distribution line

(a) Inspection for detecting faulty insulators shall be periodically performed every 5-year. At this time, in case of insulators installed on a new line, the interval of detection of it shall be calculated on a delivery date basis.

(b) Detection of faulty insulators shall be performed every 3-year to the insulators on the lines where an inferior insulator occurs or is worried to occur.

(c) Maintenance department shall adjust the inspection interval by years of manufacture to the lines required to be managed an aging deterioration as a result of inspection to the insulators.

3.1.2 Insulators on the 11kV distribution line

There is no interval of inspection for detecting each faulty insulator periodically on the 11kV distribution line. but, in case of being founded faulty or faulty-doubted insulators in


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the process of patrol focusing on visual inspection to 11kV distribution lines, those insulators shall be tested as the same methods as insulators on the 66kV or 30kV distribution line.

3.2 Inspection method

3.2.1 Suspension insulator

When insulators become deteriorated, many kinds of phenomenon occur.

First, microwave including many kinds of interval components will occur. Secondly, as leakage current flows on the surface of insulators, the temperature on the surface of them will increase and furthermore lights may occur due to partial discharging phenomenon. And this deteriorating of insulators will make their insulation resistance lowered and voltage allotted to insulators deteriorated. These phenomena are factors that weaken insulators and for the long time, it will cause insulator damaged and bring about line faults.

The methods used to inspect faulty insulator on site are as followings;


(a) After climbing poles or tower, look for fractures, chips, deposits of dirt, salt, cement dust, acid fumes, or foreign matter which under moist conditions may cause a flashover.

(b) Check for cracks in insulators by tapping gently with a small metal object only when de-energized, about the size of a 15 centimeter wrench. Insulators free of cracks emit a ringing sound when tapped; cracked ones sound dull and hollow. To avoid damaging good insulators, tap them; do not hit them hard.

3.2.1.2 Insulation resistance measurement

This measurement is measuring methods to measure insulation resistance, using a megohmer (1,000V meggar). First, after immersing insulators to be measured, polish the surface of them and dry, measure insulation resistance is more than 1,000 MΩ.

If the value is less than 1,000 MΩ the there is possibility that cracks occur at the head of insulator. But this test is available on a dead line and the reliability of it is low such that insulators in good condition over 1,000 MΩ are evaluated as inferior goods.


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3.2.1.3 Distributed voltage measurement of insulator

It is method of measuring the difference in potential across each insulator and is available to decide whether insulator is a good condition on site by reading the measured values.

Capacity of each insulator in a string is different by its locations, and it makes the sharing rate of line voltage different. In case of a 3-insulators string, the voltage distributed to an insulator on the line side will become the biggest and the one on the middles of insulator in a string will become the lowest. But if an insulator is deteriorated, the voltage distributed on it becomes lower than healthy one and 0 (zero) extremely if the insulation resistance is 0.

This measuring method is evaluated as the best in detecting the faulty suspension insulator.

Table 17 Example of faulty insulator detector

Maximum using

voltage (kV)

Maximum scale

(kV)

Tool for

measurement

Voltage

measurement

Judging of

condition Manufacturer

35 11 Universal fool(8”)

Measuring of

charging voltage

flowing

on an insulator

In case of about

below 30%

than normal

measurement value

AB Chance

company

3.2.2 Pin insulator


This inspection shall be performed by the same as methods of inspecting a suspension insulator.

3.2.2.2 Ultrasonic noise detector (Ultra phone)

This method is to judge the condition of a pin type insulator by detecting the strength of a radio wave or an ultrasonic wave (about 40khz) emitted by the internal discharge of an


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inferior insulator by reading a meter or listen to a sound through a receiver composed of a parabolic reflector and ultrasonic microphone. The receivable range of ultrasonic is below 20 to 30m and therefore, it is used for the purpose of judging the condition of a pin type insulator at the ground.

But, there are possibilities of misjudgment due to a surround noise. Therefore it is necessary to try to do high sensitive measurement considering the direction, sensitivity and measuring distance of microphone. This method has many difficulties to measure, even attending to engine noises of driving cars, etc.

3.3 Results

(a) Results of faulty insulator detection shall be recorded and managed on the faulty insulator detection record.

(b) When found, inferior insulators shall be promptly replaced as soon as possible on the de-energized condition.

(c) In case that inferior insulators occur during the insurance terms, the detection department shall submit a report about the defect occurrence to the distribution networks maintenance sub-department in regional department. And the distribution networks maintenance sub-department shall inform it to the stores and purchasing department so that the inferior insulators shall be managed by the defect management guideline.

(d) The predictive maintenance division shall perform the testing of aging changes through extracting sample insulators and consider countermeasures after conferring with the general department of distribution.

4. Cleaning of insulators Line insulators are made of ceramic and polymeric materials. Cleaning distribution insulators entails different concerns than transmission line insulators due to the lesser voltage involved and the respective clearance distances. The insulator shall be washed so that the watersheds just cleaned will maintain adequate insulation. (For example, on vertical insulators the washing would be started at the bottom and work upwards.) One of the main concerns of washing is the potential problem of overspray. When overspray presents a problem, washing from different positions may help, but will take more time and reduce production.


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4.1 Interval of insulator cleaning Interval of cleaning varies depending upon the degree of contamination, the weather conditions, and the particular insulator design.

4.1.1 Interval of cleaning

The interval of insulator cleaning is as following table 2. But, the manager of maintenance department shall adjust the number of cleaning interval, depending on a pollution condition of insulators on site.

Table 18 Interval of insulator cleaning

(Unit: year)

Pollution level

Voltage I II III IV

66kV 4 4 2 2

30kV 2 2 1 1

11kV 4 4 2 2

(1) Interval of insulator cleaning shall be increased, depending on the characteristics of

regional pollution to the areas where a fault occurs or would be assumed to occur due to pollution and pollution rapidly is developed.

(2) Insulators shall be washed prior to the time of reaching the critical contamination level. This point can be estimated from the following:

(a) Past experience on periods between flashovers, or pole fires

(b) Allowable equivalent salt-deposited density (ESDD) obtained from de-energized test insulators or from energized insulators

(c) Degree of scintillation during damp weather conditions

(d) Complaints of radio/television interference

(e) Proximity and exposure to the pollution source

(f) Type of contaminant, and its rate of buildup on the insulator

(g) Weather conditions (it is noted that the danger of flashover and pole fires is


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particularly great after a long, dry period, either in winter or summer, followed by a light drizzle or fog condition)

(h) Sensor insulators that indicate contamination level (to be used for areas of consistent contamination levels or worst-case areas)

Table 19 Pollution level by equivalent salt deposit density (ESDD)

Pollution level I II III IV

ESDD Below 0.03 to 0.06 0.10 to 0.20 0.30 to 0.60 -

4.1.2 Time of cleaning

(1) The time of insulator cleaning is in principle as following, the manager of maintenance department could have the cleaning performed after adjusting it depending on conditions.

(a) In case that cleaning interval is 1 time: before September

(b) In case that cleaning interval is 2 times:

• First half of the year: April to May

• Second half of the year: July to August

(2) In case that there are possibility of being frozen in the process of water washing, insulator cleaning work shall not be performed.

4.2 Insulator cleaning method

4.2.1 Polymer insulators

Manufacturers shall be consulted prior to cleaning for advice on their respective products and applicability of cleaning methods.

4.2.1.1 General guidelines for water pressure washing

Table 20 shows a general guide for washing different types of polymer insulators with water pressure washing.


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Table 20 Water pressure washing for polymer insulators

Type Water pressure Remark

Silicone

(Direct molded units)

Low- to high-pressure water washing

(200 psi to 1,000 psi)

This type of insulator is used on the 30kV

distribution line of GECOL

4.2.1.2 Other cleaning procedures

Polymer insulators may be cleaned by methods other than water washing.

(1) De-energized cleaning

If the insulators can be de-energized for cleaning, they may be hand washed with rags or wiping cloths in mild detergent water. This shall be followed by a low-pressure flood rinse with clean water to remove any residue. Solvents or harsh abrasives are normally not recommended. Wetting agents or additives can be used to improve the washing action of the cleaning water. Solvents may be used, provided all cleaning residue is removed by the final clean water rinse and only after manufacturer approval.

(2) Energized cleaning

Compressed air/dry abrasive cleaning: This procedure involves the use of compressed air and dry abrasive cleaning media. The abrasive cleaning compounds often consist of ground corncob mixed with ground walnut or pecan shells.

The actual cleaning process is similar to sandblasting in that a pressurized air stream is used to bombard the insulator surface with abrasive media. After cleaning, the contaminant and abrasive residue remaining on the insulator surfaces are blown off with dry, clean, compressed air.

With proper cleaning media and procedures, virtually any contaminant can be safely removed from the insulator surfaces without the need for area cleanup of the abrasive residue. Abrasive cleaning techniques are not recommended for silicone rubber insulators since they can temporarily destroy the surface hydrophobicity of the polymer.

4.2.2 Ceramic insulators

Porcelain and glass insulators with galvanized hardware are the most common insulators to


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be cleaned. Any cleaning technique used shall not damage or deteriorate the item to be cleaned. Ceramic insulators can be cleaned in a number of ways, and they can either be energized or de-energized.

The most common methods used are the following:

(a) High-pressure water (400 psi to 1,000 psi) cleaning

(b) Medium-pressure water (300 psi to 400 psi) cleaning

(c) Hand cleaning

4.2.2.1 Energized

(1) Pressure water

(a) High-pressure water

High-pressure water washing utilizes a narrow stream of water with typical pressures ranging from 400 psi to1000 psi at the nozzle.

(b) Medium-pressure water

The concept of medium-pressure washing has proven to be effective. This system involves many of the same procedures used in the high-pressure handheld and remote-control jet nozzle procedures. While effective washing is maintained, the advantages are reduced equipment stress and employee fatigue because of the lower operating pressures. Tests indicate that the leakage currents through the water stream using this method are within safe operating limits. The pressures used for this method are in the 300 psi to 400 psi range

(2) Handheld jet nozzle

The handheld nozzle is the most common type of nozzle used for high-pressure washing. The line worker either climbs the tower or uses an aerial lift to raise the hose and nozzle to the wash position. The line worker may also connect a detachable hose and nozzle to a standpipe permanently installed on the tower.

Substation insulators may also be washed using a handheld nozzle while on the ground or in


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an aerial basket.

(a) The resistivity/conductivity of the water from the wash truck reservoir shall be checked by a resistivity/conductivity meter each time water is added. The wash truck is positioned so that the wash hose will come off the hose reels at the tower leg to be climbed. In this way, the hose does not have to be dragged around the tower.

Wire braid conductive hose is connected to bond the truck to the tower. The continuity of this bonded connection is checked prior to the start of the job. Routinely, all bonding connections shall be checked for corrosion and cleaned, as required. Since the wash truck may acquire a relatively high potential, it is important when washing that no person gets on or off the truck and that all persons on the ground are kept away from the truck. Persons on the truck must also avoid reaching out and touching adjacent trees, poles, towers, or other objects.

(b) Next, the qualified worker climbs the tower carrying a hand line. The truck driver sends up the hose, gun, and nozzle. The qualified worker bonds the nozzle to the tower steel or pole bond wire. The point is that the qualified worker, the nozzle, and the tower must be at the same potential.

The qualified worker then directs the truck driver to increase the water pressure. If the unit is equipped with a demand throttle, the pressure (revolutions per minute - rpm) will be automatically increased when the gun is opened. The water is directed away from the insulator string until full pressure has been achieved. The line worker on the tower then directs the wash stream at the insulator. The nozzle-to-conductor distance shall not be less than the established minimum wash distance. See Table 5.

(c) Suspension insulator strings are washed by first directing the stream of water at the insulator nearest the energized conductor in such a manner as to take advantage of both the impact and the swirling action of the water to remove deposits. After the bottom insulators in the string are washed, the wash stream is moved up a few units. These units are washed and the stream then is directed on the clean units below to re-rinse them. This process is repeated, moving up a few insulators at a time until the entire string is clean. Failure to rerinse lower insulators before moving further up the string can lead to flashover. The stream must be moved away from any energized part of the insulators before the water pressure is reduced. Care shall be taken to prevent the spray from unduly moistening nearby dirty insulators, particularly in the station.

(d) Deadend insulators must be washed carefully to keep overspray from causing


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flashover. Begin washing on the downwind end of the insulator string and then work upwind.

It is important that the above procedures and the established wash parameters are strictly adhered to when conducting hot-line washing.

4.2.2.2 De-energized

All of the methods discussed in 4.2.2.1 may also be utilized in addition to hand cleaning, when the facility is deenergized (and grounded). When the system is de-energized (and grounded), the requirements of water resistivity are the same as for an energized system. However, the clearance issue is not there, thereby allowing different washing conditions.

(1) Hand cleaning

Cleaning insulators by hand wiping is thorough and effective, but it is also a tedious, time-consuming, and expensive process that requires equipment outages. Hand wiping is generally used only when washing is impractical because of problems of access by heavy vehicles, height or design of structures, or type of contamination. Hand wiping is normally used on station insulators where high-pressure washing is either impractical due to proximity of energized equipment or ineffective due to hardness of surface deposits.

Some insulators can be cleaned using only soft, dry wiping rags. Additional materials, such as wet or paraffin-soaked cloth, solvents, steel brushes, or steel wool, may be needed for other insulators.

(a) Nonabrasive nylon pads

Nonabrasive nylon pads are used when rags and paper towels are ineffective.

(b) Steel wool

Steel wool is sometimes used when rags and paper towels or nylon pads are ineffective. Caution shall be exercised to remove all the metal particles left by the steel wool.

(c) Solvents

Solvents may be used to aid the cleaning. Care shall be taken with strong cleaning agents because of fumes or residue. After cleaning, the insulator shall be rinsed with clean water


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to remove residue. For polymeric insulators, in general no solvent can be used, unless advised by the manufacturer.

4.3 Results Results of efficient insulator cleaning can be judged by the following.

4.3.1 Visible (clean-shiny)

Surface condition of both the top and bottom of the insulator skirts shall be visually clean and shiny after the water or solvents have dried.

4.3.2 Insulator vibration (ringing)

Mechanical vibration (ringing) of insulator skirts under impact of high-pressure washing and exhibiting evidence of efficient swirling cleaning action.

4.3.3 Absence of corona

Blue corona discharges extend from the metal cap to the porcelain during energized high-pressure washing and may be heard for a few seconds after completion of cleaning.

If this discharge continues for more than a few seconds, it may indicate incomplete washing of the insulators, in which case the wash stream shall be reapplied.

4.3.4 Clarity of runoff

Clarity of the water runoff may also indicate the effectiveness of contamination removal. Clarity of water runoff may be difficult to observe due to distance, sunlight, wearing of sunglasses, etc.

4.4 Technical considerations for energized cleaning with water

4.4.1 Leakage current

Leakage current is defined as the current that flows through normally nonconducting elements such as hoses.


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The level of 1 mA is the approximate perception threshold current that a person detects as a slight tingling sensation in his hands or fingers due to current flow. When the nozzle grounding braid is properly grounded, no appreciable leakage current shall flow through a person’s body during the washing operation. Nevertheless, a person shall anticipate the possibility that the nozzle grounding braid can accidentally open or become disconnected. For this reason, leakage current in the wash stream shall be limited to 2 mA.

The washing equipment, the wand, the structure, and the washing person shall be at the same potential.

In substations, nozzle operators using handheld nozzles wear rubber boots, rain clothes, and rubber gloves to avoid getting wet. In addition, the wet hose is in direct contact with the ground. The operator has both hands on the nozzle while the stream is contacting energized equipment. It shall not be difficult under these circumstances to limit the leakage current by adjusting washing distance, pressure, orifice, and water resistivity.

The parameters that influence the leakage current in the wash water stream are as follows:

(a) Line voltage

(b) Distance from the nozzle tip to the energized parts

(c) Water resistivity or conductivity

(d) Water pressure

(e) Nozzle orifice diameter

Currents exceeding 1 or 2 mA are to be guarded against by the following:

(a) Using water that falls within the acceptable range of conductivity or resistivity

(b) Replacing worn nozzles

(c) Carefully maintaining safe working distance


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4.4.2 Working distance

Table 21 Minimum distance for energized washing

Line voltage

(kV)

Minimum nozzle-

to-conductor

distance

(m)

Minimum water

resistivity

(Ω•cm)

Minimum nozzle

pressure

(kPa)

Maximum orifice

diameter

(mm)

2.74 5000 2758 4.76 66

3.66 5000 2758 6.35

2.44 5000 2758 6.35 30

2.44 5000 2758 4.76

1.82 5000 2758 4.76 11

1.82 5000 2758 6.35

Nozzle-to-conductor distance for a given line voltage and nozzle diameter is the most important parameter that influences the leakage current and the washing effectiveness of the water stream. Washing effectiveness and the magnitude of leakage current decrease with increasing nozzle-to-conductor distance. In cases where the wash distance is limited by the tower dimensions, demineralized water can be used.

Table 5 gives minimum distance between the energized parts and the nozzle tip for various line voltages.

4.4.3 Establishing a maximum stream length distance

Everyone involved with cleaning energized insulators understands the need for establishing a minimum stream length distance. The maximum distance between the nozzle and the insulators being washed is the distance that a high-pressure compact stream can be maintained. The compact stream is more effective in washing contaminants from the insulators and can be directed with better accuracy to avoid wetting adjacent unwashed/energized insulators. Beyond that distance, the stream will break into a spray, which can result in insulators not getting adequately washed, or in the worst-case scenario, flashing over the insulator.

Also, failure to establish a maximum distance can place the worker at risk and affect the reliability of the circuit being washed. When establishing the maximum stream length distance, the following, additional factors need to be considered:


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(1) Type of insulator to be cleaned

(a) Cap and pin

(b) Post

(c) Ball and socket

(2) Insulator configuration

(a) Vertical

(b) Horizontal

(3) Stream impact on insulator surface

(4) Contamination level on insulator surface

(5) Configuration of the wash stream at a given distance

Each of these factors shall be considered in establishing the maximum stream length distance that can be used and still provide a safe and effective cleaning.

Tests proved that insulator cleaning is ineffective when performed from too great a distance, and all that is actually accomplished is a wetting of the surface of the insulator, which can increase the risk of flashover. Everyone who performs energized insulator cleaning using pressurized water must consider establishing a maximum stream length distance. This will help to ensure that an effective wash is achieved and reduce the risk of insulator flashovers.

4.4.4 Water quality

4.4.4.1 Water resistivity

This is the insulating value of water. The unit to measure the resistivity of water is the ohm-centimeter or ohm-inch. This is determined by measuring the resistance between opposite faces of a cube of water, 1 cm or 1 in one apart.

Water resistivity or water conductivity is another important parameter that influences the leakage current of the water stream. A low value of water resistivity could lead to insulator flashover or injury during washing.

NOTE 1: Ohm is a measure of resistance. Ohm-cm is a measure of the resistivity. The higher the reading, the better the quality of water. Microsimens/cm is a measure of


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conductivity. The lower the reading, the better the quality of water.

Test conductivity with each filling of the tank. If the reading does not fall within the acceptable range, obtain water from another source.

NOTE 2: To convert ohm-inch into ohm-cm, multiply by 2.540. To convert ohm-cm into ohm-inch, multiply by 0.3937. The following table shows some typical values (here 2.5, not 2.54 is used to convert from Ω•cm to Ω•inch):

Table 22 Water resistivity/conductivity

Resistivity

(Ω•cm)

Resistivity

Ω•in (Ω•cm/2.5)

Conductivity

μS/cm

5,000 2,000 667

Water having a resistivity greater than 5,000Ω•cm (2,000Ω•in) shall be used and can usually be obtained from city hydrants.

4.4.4.2 Water temperature

As the temperature of water increases, its resistivity decreases. In other words, the conductivity increases with the increase of temperature. Because the water resistivity changes with temperature, it is necessary to measure resistivity periodically, especially in hot weather.

To prevent water from heating up, the pump must be idled back and the recirculating valve opened when washing is not in progress. Water that has been in the hose long enough to warm up must be flushed out before washing starts.

4.4.4.3 Water resistivity measurement

An instrument to measure the resistivity/conductivity of the water is required, since it is very important that the washing crew know the resistance of the water before using it to clean energized insulators, to ensure that the resistivity is sufficiently high.

(1) Resistivity meters

Commercial resistivity/conductivity meters are available in portable models, which are


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utilized for testing of each tank of water before and after filling (before hot washing).

A constant resistivity monitoring system provides continuous metering of the water resistivity while the washer is operating. It consists of a remote probe with a sensor lead from the bottom of the tank outlet and provides for metering and washer control.

NOTE: The tester shall be non-temperature compensated.

(a) Portable handheld

A portable handheld resistivity meter shall be utilized for testing the resistivity qualities of water sources before filling the washer tank. Also, wash practices shall call for testing of each tank of water after filling, before hot washing, unless the washer is equipped with a constant monitoring system.

A typical tester has a self-contained sample well, a padded unbreakable case, is powered by a battery, and has a battery test and calibration circuit. The meter has a display in ohms per cubic inch or ohms per cubic centimeter with minimum limits highlighted in red and accurate to within ±2% of full scale.

(2) Continuous monitor

Hard-mounted solid-state circuitry, with a waterproof high impact case and meter scales as previously described, is utilized. A remote probe with a lead from the tank bottom outlet provides a sensor for the meter and control. A continuous measurement of the water is made while the unit is operating. An operator warning and complete shutdown occurs if the minimum preset resistivity limit is reached.

NOTE: If de-ionized or boiled water of high resistivity is utilized for washing, a dual range meter may be required.

4.4.5 Water supply

Washing water may be obtained from a municipal supply or other clean source, such as a running stream. Water containing chemicals or salts must not be used. Under no circumstances shall detergents be added to the water. Only approved chemicals, such as polymer additives, may be added to the water. The operator must make sure there is sufficient water in the tank to finish the job once it is started.

Each tank of water must be tested even if the water has been taken from a source that


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previously tested good. The conductivity of all water used for washing insulators must be within the limits.

A tank of water that has warmed up since it was originally tested must be retested to ensure that it still meets resistivity requirements.

4.4.6 Water pressure

Water pressure is related to the working distance and may be adjusted accordingly. The pressure will decrease as the distance increases, and if the distance is too far, washing will not be effective. Safe working distances must always be maintained. The cleaning effect is directly related to the water force or impact of the water on the insulators. High water pressure and a compact stream are required to

(a) Perform the best cleaning job with the smallest amount of water.

(b) Cut down overspray and hence minimize the flashover of insulators during washing.

(c) Ensure that sufficient water can be delivered to extinguish an electrical arc shall it develop.

4.4.7 Nozzles

The size and design of the nozzle orifice affects the size and performance of the water stream, thus affecting the water pressure and leakage current. The nozzles must be inspected daily when in use. If nicks, which would cause the water stream to break into a spray, are observed, the orifice must be rehoned. Worn out nozzles that do not do a satisfactory cleaning job must be repaired.

4.4.8 Grounding

The body of the truck is insulated from ground by the tires and can thus become a large capacitor. If the truck is not grounded, it is possible that it can build up charge to a dangerously high voltage. Hence, the truck must be grounded while washing is in progress. It is of utmost importance that no human contact be made with the truck to avoid establishing a parallel ground through a person’s body. Adherence of the requirements stated in the preceding subclauses will limit the leakage current to safe limits. Additional protection is provided by placing the washing gun operator in an equipotential zone by bonding and grounding appropriately.


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Faulty Insulator Detection Record Line

name T/L (D/L) Working time Weather

Description Faulty information Name of detector

Total number of insulators EA

Inspected insulators number EA

Faulty insulators number EA

Working

content

Faulty rate %

#1 T/L (D/L) #2 T/L (D/L) Tower

(Pole)

number

Source

side

Load

side

Year of

Manufacture Manufacturer

Source

side

Load

side

Year of

Manufacture Manufacturer

Foreman : Office/Section supervisor :


Date : Date :


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Insulator Cleaning Report Cleaning Date: 200 . . . Whether & Temperature: , ºC

Line name T/L (D/L)

Total cleaning number Line voltage kV

Water resistivity Ωcm

Water temperature ºC

Nozzle orifice size Energized

Grounding condition

Cleaning method

De-energized Cleaner type

Name

Worker

#1 T/L (D/L) #2 T/L (D/L) Tower (Pole) number

Cleaning

Number Source side Load side Source side Load side Remark



Date : Date :


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XII. Distribution Transformer


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1. General

1.1 Description The transformer that connects the high voltage primary system (4.16 kV to 34.5kV) to the customer (at 480 volts and below) is usually referred to as a “Distribution Transformer”. These transformers can be either single-phase or three-phase and range in size from 5 kV to 1,000kVA.

1.2 Types of distribution transformer Distribution transformer is divided into ground-mounted transformers and pole-mounted transformers by installed locations. Ground-mounted transformers, used for underground service come in about the same ratings and sizes with the exception that 3 phase ground- mounted unit can be rated as high as 2,500 kVA.


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1.3 Structure

1.4 Rating

Rated power (kVA) Type of transformer

Single-phase Three-phase

Pole-mounted 50, 75, 100 50, 75, 100, 200, 300

Ground-mounted - 300, 500, 750, 1000

(1)

(2) (3) (4) (5) (6) (7)

(8) (9)

(10) (11)

(2) (4)

(12)

1. Lifting lugs

2. Drain valve

3. Thermometer pocket

4. Earthing terminals

5. LV neutral bushing

6. LV bushings

7. Filling hole

8. Off-circuit tap changer

9. HV bushings

10. Securing lugs

11. Rating plate

12. Underbase with rollers (roller base)


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2.1 Delivery When an overhead crane is used for unloading, the transformer must be lifted by means of a cling and spreader bar utilizing the tank-mounted lifting lugs. Do not lift the entire unit with the lifting eyes on the cover. The lifting eyes are only to be used to untank the internal assembly which is attached to the cover.

2.2 Storage If the transformer is not to be placed into immediate use, it can be stored with minimal precautions. Store the unit where the possibility of mechanical damage is minimized.

3. Inspection

3.1 Field inspection before operation Before connecting the distribution transformer to the line, perform the following inspection.

(a) Check oil gauge. Look for visible signs of oil leakage.

(b) Examine series arrester for damage, if any. If damaged, install a new arrester of same voltage rating.

(c) Inspect porcelain bushings for damage or leaking seals. If there is a suspicion that moisture has entered unit, remove handhole cover and inspect for evidence of moisture such as rust or water tracks in oil. If moisture has entered that tank, dry transformer and filter oil before putting unit in service. Refer oil test method of power transformer, for values that oil shall meet. Be sure to properly replace handhole cover.

(d) Check indicator for damage. When cleaning the faceplate, do not use solvent or fuel.

(e) If regulator has been stored for some time, test dielectric strength of oil.


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3.2 Daily inspection Daily inspection of distribution transformer shall be performed in the process of patrol through regular visual checking a transformer without any interruption.

(a) Check any corrosion, rust, contamination on main body or bushing

(b) Check the status of oil through oil level gauge.

(c) Check operation status of over pressure relief valve

(d) Read and record the oil temperature indicators provided on the transformer.

(e) During the inspection, pay attention to any abnormalities such as noises, irregular vibration, discolorations, smoke etc.

(f) Record ambient temperature, load and voltage

(g) Perform IR scan



Routine inspection of distribution transformer shall be performed every 3-years.


(1) Transformer temperature

(a) Check and record the oil temperature.

(b) Record ambient temperature, load and voltage.

NOTE 1: The transformer temperature directly affects the life of the insulating material.

NOTE 2: The maximum temperature rise limits are specified for both oil and winding temperature. During the daily inspection, check not only that temperatures are within the maximum limit, but also that these temperatures lie within a satisfactory range by comparing their values with the test results in the test report, load conditions and ambient temperature.

(2) Oil level


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- Check and record the level of oil shown by the oil level gauge.

- Check that the glass of oil level indicator is not dirty.

(3) Noise

- Check for any abnormal sound and vibration etc.

Note: Learn by hearing an average and regular sound; If an irregular noise is heard, compare with remembered normal sound and further investigation should be done immediately.

(4) Oil leakage

- Check for oil leaks at any connections such as valves, meters and particularly welding points.

(5) Breather

- Pay attention to the discoloration of the silica gel.

(6) Pressure relief

- Check for cracks, damages and traces of oil overflowed from the pressure relief device.

(7) Bushing

- Check visually the extent of any contamination on the bushing.

- Check the over heat of terminals.

(8) Loose connections

- Check for any loose connections such as connectors of main circuits, grounding circuits, foundation bolts and the like.

(9) Mounting platform

- In case of pole mounted distribution transformer, check the condition of mounting platform.


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(10) IR scan

- Perform IR scan to check abnormal part.

(11) Sampling oil (if necessary)

- Test dielectric strength of sampling oil after extracting it from oil sampling cock, if necessary.

- Dielectric strength of oil test method is the same as a power transformer.


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Distribution Transformer Routine Inspection Inspection date: 200 . . . Weather & Temperature: , ºC

Installation site Distribution TR ID Voltage

kVA Rating Serial number

Plant of Manufacture Year of Manufacture

Item Check points Inspection result Remark

Check enclosure & main body Corrosion, rust, contamination

Insulating oil Oil level, leakage,

Ambient temp. Ambient temperature ºC

HV cable Cable temperature ºC

Main body Insulating oil temperature ºC

Temperature

measurement

2nd bushing Low voltage terminal ºC

X1 A X1-X2 V

X2 A X2-X3 V

X3 A X3-X1 V Load current

X0 A

2nd Voltage

-

IR scan Infra red scan to all parts

Ground resistance Below the standard of ground resistance Ω

Sampling oil Dielectric strength When necessary

Breather (silica gel) condition

Pressure relief

Bushing

Connection of main(grounding) circuit, bolts

Mounting platform

General item

Any noise, vibration



Date : Date :


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XIII. Power Capacitor Banks


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1. Generals

1.1 Description Power capacitors for use on electrical distribution systems provide a static source of leading reactive current. Power capacitors normally consist of aluminum foil, paper, or film-insulated cells immersed in a biodegradable insulating fluid and sealed in a metallic container. Depending on size and rating, they are available as either single- or three-phase units. Power capacitors are rated for a fundamental frequency, voltage, and kilovar (kilovoltamperesreactive) capacity and are generally available in voltage ratings up to 34,500 volts and 200 kilovar. Individual units may be connected in series and multiples to provide banks of various capacities and voltage ratings.

1.2 Types of power capacitor The terms “series capacitor” and “shunt capacitor” are used to identify the type of connection and do not indicate a difference in the power capacitor construction.

1.2.1 Series power capacitors

Series power capacitors are primarily used for voltage regulation and receive very limited application in electrical distribution systems. In the usual application for power service, the series-capacitor kilovar rating is too low to improve the power factor significantly.

1.2.2 Shunt power capacitors

The shunt power capacitor is a capacitive reactance in shunt with the electrical load or system and is fundamentally provided for power-factor improvement. The benefits of improved voltage level, released system capacity, reduced system losses, and the reduction in the power bill all stem from the improvement in power factor.


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1.3 Structure

Figure 27 Example of pole mounted capacitor bank installation (Qpole by ABB)

1.4 Rating

Nominal Voltage (Line to Ground/Line to Line) 6,350/11,000V 17,320/30,000V

System highest voltage 12kV 36kV

Number of phases 3

Number of capacitor units 3

Rated frequency 50Hz

Lightning impulse withstand voltage 75kV 170kV

Power frequency short duration withstand voltage 28kV 70kV

Connection of the bank Star (Neutral point unearthed)

Operation place Outdoor

1.5 Application Shunt capacitors are used on distribution circuits to reduce the kilovoltampere load on a low power factor circuit. Fixed shunt capacitors are used to improve the voltage level and


- 184 -GECOL

switched shunt capacitors are used to improve voltage regulation. All capacitor banks shall be equipped with a means to disconnect them from the electric system.

1.6 Capacitor unit capabilities Capacitors are intended to be operated at or below their rated voltage and frequency as they are very sensitive to these values; the reactive power generated by a capacitor is proportional to both of them (kVar ≈ 2 π f V2).

These standards stipulate that:

(a) Capacitor units shall be capable of continuous operation up to 110% of rated terminal

rms voltage and a crest voltage not exceeding 1.2 x 2 of rated rms voltage, including harmonics but excluding transients. The capacitor shall also be able to carry 135% of nominal current.

(b) Capacitors units shall not give less than 100% nor more than 115% of rated reactive power at rated sinusoidal voltage and frequency.

(c) Capacitor units shall be suitable for continuous operation at up to 135%of rated reactive power caused by the combined effects of:

• Voltage in excess of the nameplate rating at fundamental frequency, but not over 110% of rated rms voltage.

• Harmonic voltages superimposed on the fundamental frequency. • Reactive power manufacturing tolerance of up to 115% of rated reactive power.

1.7 Considerations

1.7.1 Ensuring safe capacitor de-energizing

Capacitors retain a charge after they are de-energized. After capacitors are de-energized allow at least 5 minutes for discharge and then short the capacitor terminals to ground and to each other. These grounding provisions shall remain until work on the installation is completed. Although most power capacitors have a discharge resistor installed to automatically discharge them after they are disconnected from the circuit, it is not advisable to depend entirely on such resistors for safety.

1.7.2 Ventilation of power capacitors


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Power capacitors are very efficient but do generate some heat which must be adequately ventilated. Make sure that airflow around the individual capacitor units is not obstructed. Be especially careful in checking vertical capacitor banks, where heated air around the lower units rises to the top rows. Improperly ventilated housings on such installations may result in excessive operating temperatures.

1.7.3 Temperature influence on power capacitors

Power capacitors are designed for operation at a maximum ambient temperature as given in table 23 (which occurs at rated voltage and frequency and while subjected to the direct rays of the sun). Conditions resulting higher operating temperatures may injure the insulation and shall be avoided. Capacitors are designed for continuous operation at a maximum ambient temperature of 40 ºC. Capacitors that are normally de-energized, or operate intermittently at or below an ambient temperature of minus 20 ºC, shall be carefully inspected. At extremely low temperatures liquid insulation can crystallize which decreases insulation strength and failure may occur when the capacitor is re-energized. For installations where low temperature is a problem, units shall be kept energized.

Table 23 Ambient temperature for continuous operation

Description of temperature Temperature limit (degree C)

Maximum ambient air temperature + 50

Minimum ambient air temperature - 10

Monthly average temperature of the hottest month + 40

Yearly average temperature + 30

1.7.4 Exposure influence on power capacitors

Care shall be taken to eliminate or minimize exposure of capacitors to damaging fumes or vapors, salt air, unusual dampness, contamination, abnormal shock, or vibration. Corroded or rusted capacitor cases and mountings shall be cleaned and painted. Capacitor bushings and busbar supports, subject to accumulation of dust or foreign materials, shall be cleaned periodically. The intervals will depend on the severity of the condition.

1.7.5 Voltage influence on power capacitors

Shunt capacitors cause a voltage rise at the point where they are located and are likely to operate at overvoltages. Capacitors are designed to operate continuously up to 110 percent


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of rated voltage rms; provided that the crest voltage, including all harmonics, does not exceed 1.2 times the square root of 2 times the rated rms voltage; and provided that the 135 percent maximum permissible rated kilovars has not been exceeded. Since operation in excess of voltage and temperature limits may shorten the life of a capacitor, the voltage shall be checked periodically to ensure that it is within design limitations.

1.7.6 Fuses for power capacitors

A capacitor fuse is not used for overload protection in the same manner as a fuse is used for overload protection of other electric apparatus. The current rating has to allow for inrush current, and capacitor fuse ratings typically range from 165 to 250 percent of the capacitor current rating. Fuse ratings shall always be those recommended by the manufacturer, since the fuse’s time-current characteristic must be matched to the capacitor’s tank-rupture time-current characteristic. The blowing of a properly rated fuse may indicate a capacitor fault, as well as a circuit overcurrent operating condition. When inspection reveals blown fuses, do not replace such fuses until a check determines that the capacitor unit is still serviceable. When fuses are replaced, be sure they are of proper voltage and current ratings and in compliance with the capacitor manufacturer’s recommendations.

2. Handling Check the capacitor when received to make sure that no damage occurred during shipment. Minor damage such as small dents will not harm the capacitor's performance, but capacitors with large dents, leaks or broken bushings shall not be installed. In case of major damage, file a claim against the carrier and also notify the manufacturer for instructions regarding the disposition of the capacitor.

Check the capacitor's nameplate to make certain that the voltage rating is the same as the applied voltage. According to specification the recommended maximum continuous-working voltage to be applied to the capacitor shall be 110 percent of the nameplate rating.

The peak continuous working voltage, including all harmonics, shall be 1.2 x 2 x the nameplate voltage rating. Any lower voltage is permissible.

Some failed capacitors may be found considerably bulged due to internal pressure from gassing prior to circuit clearing. Such capacitors shall be handled very carefully. A failed capacitor shall be short-circuited before handling. It is further recommended that a bulged capacitor be permitted to cool before handling. This will lower the internal pressure, reducing the possibility of case rupture.


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3. Inspection

3.1 Initial inspection The initial inspection shall be made within 24 hours after energizing a new power capacitor banks installation. This inspection shall be made at a time of maximum circuit voltage, usually during the first period of light load on the circuit.

In addition to visual observations, this inspection shall include voltage and current readings to ensure that voltages and currents do not exceed capacitor rating limits. Operating kilovars (the sum of the fundamental frequency kilovars and any harmonic frequency kilovars) shall not exceed 135 percent of the capacitor rating.



Routine inspection of power capacitor banks shall be performed at least 4 times per year in energized condition.


(a) Perform an external inspection.

Inspect the tank and accessories of each bank to check rust, defect, any change, leaks.

And check whether bushings and insulators crack or are contaminated.

(b) Check the condition of terminal tightening.

The poor connection of terminal causes heating. Re-tighten the heating terminal and change a wire.

(c) Check the ambient temperature and the case temperature.

In case that ambient temperature is over 40 ºC or the case temperature exceeds 55 to 65 ºC, more detailed inspection shall be made.

(d) Check whether the terminal is in overheating.


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The maximum temperature of terminal shall be lower than 90 ºC in the condition that ambient temperature is 40 ºC.

(e) Check whether some strange smelling like when something is burned.

(f) Observe whether any transformation on the case is.

(g) Observe the operation of protective devices such as cutting of fuse.

(h) Check the indicator of ammeter.

The movement of ammeter shall not exceed 120% of rating and unbalance of each phase shall not exceed 20% than the average of 3 phases.

(i) Check the indicator of voltmeter

Bus voltage in light load shall not be bigger than 109% of rating.

3.3 Special inspection


Special inspection of power capacitor banks shall be performed in de-energized condition at least once each 3-year or when an abnormality of equipment is inspected.


(a) Check the looseness and discoloration of terminals.

(b) Check the damage of bushing insulator such as cracks, defects.

(c) Check the condition of earth wire such as disconnection of earth wire and looseness of connection screw.

(d) Measure the insulation resistance of power capacitor banks.

(e) Measure the earthing resistance.

(f) Perform the capacity test each unit.

4. Test method


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4.1 Insulation resistance measurement (a) Insulation resistance shall be measured after cleaning the bushings of power

capacitors.

(b) Perform the measurement after interrupting the circuit and ensuring there is no residual electric charge by using a voltage detector. If not, it is dangerous because there is electricity equal to the maximum voltage of circuit in the power capacitors to be tested.

(c) Measure the insulation resistance between the terminals, and between terminal and ground.

(d) Each measured value from this measurement shall exceed 1,000 MΩ.

4.2 Capacity test (a) Use a capacitance meter to measure capacitance of power capacitor.

(b) Connect the test leads to the capacitor bushings. Compare the measured value on the meter to the appropriate values in table 3. The measured values shall be fall within the range specified in the table.

(c) Shorted capacitors measure near zero; open capacitors give erratic results.

(d) If the measured values are not within the acceptable range, and there is no visible sign of failure, replace the capacitor.

(e) If the measured values are within the acceptable range, and there is no visible sign of failure, remove the shorts and grounding jumpers and re-energizing the capacitors bank.


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Table 24 Capacitance limits of power capacitor

Capacitance Unit size kVAR

Min Max

6,350 Volt μF μF

300 19.7 22.7

200 13.1 15.1

150 9.9 11.3

100 6.6 7.6

50 3.3 3.8

17,320 Volt μF μF

300 2.7 3.0

200 1.8 2.0

150 1.3 1.5

100 0.9 1.0

50 0.4 0.5

Note: Minimum capacitance: 2kV

kVAR2.65

minC =

Maximum capacitance: 1.15 CLimit Lower max

C ×=


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Power Capacitor Banks Inspection Inspection kind: Inspection date: 200 . . . Weather & Temperature: , ºC

Installation site ID Voltage

kVAR Rating Serial number

Plant of Manufacture Year of Manufacture


1. External inspection of accessories

о Dust, defect of tank and accessory

о Cracks or contamination of bushings and insulators

2. Tightness of terminals in the main circuit

3. Ambient temperature, case temperature ºC Less than 55 ºC

4. Terminal temperature ºC Less than 90 ºC

5. Abnormal smelling

6. Transformer of case

7. Operation of protective device

8. Load current Less than 120% of rating

Less than unbalance 20%

Initial

Inspection ,

Routine

Inspection

9. Voltage Less than 109% of rating

1. Looseness and discoloration of terminals

2. Damage of bushing insulator

3. Earth wire condition

4. Insulation resistance measurement

5. Ground resistance measurement

6. Capacity test

Special

Inspection

7. All the items of routine inspection

Remark




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XIV. Step Voltage Regulator


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1. General

1.1 Description To measure the quality of electric power, consumers evaluate service continuity and voltage regulation. Heavy air-conditioning and heating loads plus the ever increasing demand for electric energy can tax electric systems beyond acceptable limits. Since all electrical equipment is designed for use within narrow limits, poor voltage conditions can result in undesirable and unacceptable equipment performance such as distorted TV reception, flickering lights and/or burned out motors. Step voltage regulators on distribution systems deliver dependable voltage levels, to meet customer demands for improved voltage control.

1.2 Rating

Nominal voltage (V) Load Current (A) Rated kVA BIL(kV)

50 32

100 64

150 95

200 127

300 191

400 254

500 318

6,350/11,000Y

600 381

95

50 87

100 173

150 260

200 346

17,320/30,000Y

300 520

150kV


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1.3 Structure (Single-phase voltage regulator by Cooper electric company)

High-voltage terminals (3)

High-voltage bushings (3)

Internal assembly

HI-AMPtm upper limit switch

Upper filter press and oil fill

Shunt arrester mounting

Regulator lifting lugs

kVA label

Laser-engraved nameplate

Tank grounding

Bolt-down provisions (4)

Series arrester (MOV)

Cover-mounted terminal

Block enclosure

HI-AMPTM lower limit

Switch (hidden) Automatic pressure relief device

Tap position indicator

Oil level sight gauge

Control cable

Control enclosure

Laser engraved nameplte

Pole mounting brackets (2)

Drain valve and oil


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2.1 Delivery When an overhead crane is used for unloading, the regulator must be lifted by means of a cling and spreader bar utilizing the tank-mounted lifting lugs which are shown in figure 1. Do not lift the entire unit with the lifting eyes on the cover. The lifting eyes are only to be used to untank the internal assembly which is attached to the cover.

2.2 Storage If the regulator is not to be placed into immediate use, it can be stored with minimal precautions. Store the unit where the possibility of mechanical damage is minimized.

3. Inspection

3.1 Field inspection before operation Before connecting the regulator to the line, make the following inspection.

(a) Check oil sight gauge. Look for visible signs of oil leakage.

(b) Examine series arrester for damage. If damaged, install a new arrester of same voltage rating.

(c) Inspect porcelain bushings for damage or leaking seals. If there is a suspicion that moisture has entered unit, remove handhole cover and inspect for evidence of moisture such as rust or water tracks in oil. If moisture has entered that tank, dry regulator and filter oil before putting unit in service. Refer oil test method of power transformer, for values that oil shall meet. Be sure to properly replace handhole cover.

(d) Check position indicator for damage. When cleaning the faceplate, do not use solvent or fuel.

(e) If regulator has been stored for some time, test dielectric strength of oil.



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3.2.1 Interval of Inspection

Routine inspection of step voltage regulator shall be carefully performed every year in energized condition without interruption.


(a) External inspection of main body

• Operation condition

• Oiling of stroke end

• Corrosion

• Bolts tightness

• Modification, damages, leakage

(b) External inspection of accessories

• Cooling apparatus and their accessories

• Radiator leakage, external modification, valve condition

• Oil preservation system

(c) Tightness of terminals in the main circuit

(d) Crack, contamination and cleaning of bushings

(e) Connection condition of control circuit and connectors

(f) Operation condition of accessories and cleaning

3.3 Special inspection


Every 3-year or whenever the frequency of operation counter of SVR is over than 10,000 operation or whenever something wrong is found out, special inspection of SVR shall be performed.


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(a) Insulating oil test

Oil in a SVR shall be inspected as following methods after gathering an oil sampling from the drain valve of SVR.

- Dielectric breakdown voltage test

- Acid value measurement

- Moisture measurement

NOTE: This gathered oil sample shall be sent to GECOL laboratory or special institute for insulating oil inspection of SVR.

(b) Insulation resistance measurement

(c) Transformation, leakage, rust, cleaning condition of pressure relief device, conservator, cooling pan

(d) Packing condition of each part

(e) Inspecting and filtering of insulating oil

(f) Inspecting tap contact of OLTC

• Abrasion condition of contact

• Whether each terminal looses

(g) All the check-items of routine inspection


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Step Voltage Regulator Inspection Report Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site SVR ID

Voltage Load Current KVA rating


Inspection result Item

A phase B phase C Phase Remark

1. External inspection of accessories

о Cooling apparatus and their accessories

о Radiator leakage, conformation, valve condition

о Oil preservation system

2. Tightness of terminals in the main circuit

3. Crack, contamination, and cleaning of bushings

4. Connection condition of control circuit and connectors

5. Operation condition of accessories and cleaning

Inspection

Before

Operation ,

Routine

Inspection

6. Insulating resistance measurement (before operating)

1. Transformation, leakage, rust, cleaning condition of

pressure relief device, conservator, cooling pan

2. Packing condition of each part

3. Inspecting and filtering of insulating oil

4. Inspecting tap contact of OLTC

о Abrasion condition of contact

о Whether each terminal looses

5. Insulation resistance measurement

Special

Inspection

6. All the items of routine inspection

1. Input voltage (kV)

2. Out voltage (kV)

3. Load current (A)

4. Operation frequency (times)

General item

5. Tap location (Tap)




- 199 -GECOL

XV. Auto Recloser


- 200 -GECOL

1. General

1.1 Description An automatic circuit recloser is a self-contained device with the necessary circuit intelligence to sense over-currents to time and interrupt the over-currents and to reclose automatically to re-energize the line. Reclosers are provided with a predetermined sequence of opening and reclosing, followed by resetting, hold closed, or lockout. If the fault should be “permanent” the recloser will “lock open” after a preset number of operations (usually three r four) and thus isolate the faulted section from the main part of the system.

Most faults on overhead distribution systems-perhaps as high as 70 to 80 percent – are likely to be temporary in nature and last only a few cycles to a few seconds at the most. Automatic circuit reclosers, with their “trip and recloser” capability, eliminate prolonged outages on distribution systems due to temporary faults or transient over-current conditions.

1.2 Types of auto-recloser Automatic circuit reclosers are classified on the basis of single or three phase, hydraulic or electronic controls, and oil or vacuum interrupters. Reclosers may be insulated with oil, SF, or EPDM (silicon-ruber). They may be magnetically or electronically operated. Some circuit breakers are provided with reclosing relays and other devices, which act in the same manner as automatic reclosers.

At present, GECOL uses three phase electronically controlled recloser of SF6 gas insulated or solid insulated method as automatic reclosers according to specification.

Figure 7 GVR made by Whipp and Bourne


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1.3 Structure (Model: GVR by Whipp and Bourne)

Figure 8 Circuit breaker tank assembly

Figure 9 Main features

1. Single piece, aluminium or copper-cored EPDM or

silicone rubber bushings, with grooves to take

optional wildlife guards/MV boots.

2. Current transformers are mounted within the tank’s

controlled environment, while optional capacitive

voltage divide voltage signals for use by Panacea or

an RTU.

3. Aluminum housing with lightweight, moulded

baseplate, secured by stainless steelbolts and

incorporating rubber ’O’ ring seals.

4. Pressure-relief disk offers the highest levels of safety.

5. Mechanical ON/OFF position indication visible

trough clear viewing window from ground level.

6. Hook stick-operated manual trip and lockout control.

7. A single moulding supports the three phase vacuum

interrupter assembly, magnetic actuator mechanism

and one-piece drive beam.

8. The patented, single coil magnetic actuator is based

on a solenoid plunger, held in the tripped or closed

position by permanent magnet.


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1.4 Rating (Model: GVR by Whipp and Bourne)

Product GVR15 GVR38

Impulse Withstand Voltage 110kV 150kV

Frequency 50/60Hz 50/60Hz

Continuous Current 560A, 630A 560A, 630A

Symmetrical Interrupting Current 12.5kA 10kA

Symmetrical Making Current 12.5kA 10kA

Asymmetrical Making Current 32kAp 25kAp

Weight-Recloser 145kg 155kg

Weight – Control Cubicle

Lithium Batteries 45kg 45kg

Weight – Control Cubicle

Lead Acid Batteries 95kg 95kg

Protection CT Ratio 100/200/300/1A 100/200/300/1A

SF6 Gas Filling Pressure (gauge) 0.3 Bar 0.5 Bar

Rated SF6 Gas Pressure 0.0 Bar 0.3 Bar

Control supply voltage

LiMno2 Polarr Relay (Control Units only) 90V 90V

Control supply voltage

Lead Acid Polarr Relay (Control Units only)60V 60V

Ambient operating temperature range -40ºC to +50ºC -40ºC to +50ºC


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2. Delivery and storage The recloser should be lifted off the pallet using the lifting brackets on the tank sides. And this time, the recloser should be moved far from about 30cm above ground. The sling arrangement should be such that lifting hook is above the level of the bushings and matched weight center of the recloser not to contact the left and right bushings.

Figure 28 Lifting the tank and the control box

When lifting the control box, care should be taken that the umbilical cable is not trapped or strained. Larger control boxes should be lifted a sling arrangement.

NOTE: When the recloser is lifted off, using the bushings or the terminals of bushings must be prohibited. In this case, SF6 insulating gas would be leaked or the bushing would be damaged. They would cause a fatal blow to the recloser.

3. Inspection

3.1 Field inspection before operation Before and after installation, the recloser should be carefully inspected as follows in order to verify whether there are any problems on it.


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(1) Check whether bushing is cracked and the assembling status of primary connecting terminal.

(2) Check whether the window for ON – OFF status indicator is damaged.

(3) Check SF6 gas pressure or whether gas pressure drop lamp is on.

Note: If the pressure drop lamp is on because SF6 gas leaks, stop installing the recloser and inquire the manufacture at once.

(4) Check control box

(a) Verify whether an outdoor cover of control box is attached strongly

(b) Verify whether all LED is normally operated pushing the lamp button.

(c) Check whether packing inside the door is damaged

(d) Verify the status of external appearance of batteries and connection of connectors

(e) Record polar relay setting values already calculated on the designed form.

(5) Bypass and isolate the recloser by suitable means, if possible and perform operating tests of recloser using the operation switch on the control panel and manual trip lever. Examine the switch position indicator of recloser and the status lamp of control box. Operating tests can disclose possible troubles and do prevent the accumulation of high-resistance oxides on contact surfaces.



All the reclosers shall be inspected on a month cycle or whenever they operate by some reasons.


Follow these steps to inspect a recloser and controller per the recloser inspection form.

(1) Inspecting the recloser

(a) Do visual inspection of physical conditions such as paint, bushings, cleanliness,


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gaskets of the recloser focusing on external conditions.

(b) Gas pressure condition

(2) Inspecting the control box

(a) Check up the polar relay settings comparing with the prior setting values.

(b) Check up the condition of control box

• Physical conditions such as paint, gasket, locking mechanism, cables

• Internal conditions such connections, corrosion

• Contact conditions

• All the batteries (primary and secondary) conditions

• Operating tests including lights, switches, lockout, counter

NOTE: If need, do operating tests several times after closing the bypass switches.

4. Test method

4.1 Operating test (a) Connect the umbilical cable to the tank socket.

(b) With reference to the Polarr relay manual, select local control on the front panel.

(c) Check the operation condition of recloser, pressing the open or close button

(d) Check the trip operation of recloser, pulling manual trip lever through approximately 45 degrees.

4.2 Battery test If the capacity of all the batteries which are used for operation of auto recloser becomes less than 80% of the original capacity, they must be replaced to guarantee their proper performance.

4.2.1 Battery rating


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(1) Main control battery ratings

Description Primary (Non-Rechargeable) Secondary ( Rechargeable)

Nominal Pack Voltage 90 Volt 60 Volt

Capacity 10Ah 2.5Ah

Type LiMn02

(Lithium Manganese Dioxide)

Sealed Lead (Starved Electrolyte)

(Includes 12V Polarr Relay battery)

W&B Part Number 2801115-4 4801797-T

Fuse Type Bussman MDA 8 Automotive Blade Type 10A

(2) Polarr relay battery ratings

Description Primary (Non-Rechargeable) Secondary ( Rechargeable)

Nominal Pack Voltage 15 Volt 12 Volt

Capacity 10Ah 2.5Ah

Type LiMn02

(Lithium Manganese Dioxide)

Sealed Lead (Starved Electrolyte)

(Includes 60V Polarr Relay battery)

W&B Part Number 2800817-6 4801797-T

Fuse Type Automotive Blade Type 3A Automotive Blade Type 3A

Alternative fuse type 1 1/4”X1/4” 3A TYPE F

4.2.2 Primary battery

The batteries for the main control are the Lithium Manganese Dioxide type. The manufacturers estimated life of these cells (to 80% capacity) is 10 years at 25 ºC.

Both the main control and relay batteries have sufficient capacity to provide in excess of 20,000 trip close operation.


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(a) Main control battery

Perform the operational testing. The battery condition is only indicated correctly following a close operation on the recloser.

(b) Polar Relay Battery

To find out the condition of non-rechargeable batteries, check their condition, pressing the condition verify key on the polarr relay. In case of the polar relay battery, the percentage capacity remaining is calculated.

4.2.3 Secondary battery

Check the condition of a battery, pressing the corresponding test button on the battery and charger checking facilities in the control box panel. If the battery terminal voltage is above the required threshold level, the healthy lamp will illuminate.

Note: In order to check the rechargeable batteries, additional battery and charger checking facilities are required.

Figure 29 Battery and charger checking facilities

4.3 Vacuum interrupter contact test The vacuum interrupter life is mainly dependant upon the number and magnitude of short-circuit operations. The table below shows the anticipated contact life in number of opening operations at different levels of short circuit current.


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Table 25 Anticipated contact life in number of opening operations of GVR

15.5kV 12kA 38kV 10kA

Current switched Switching life in Current switched Switching life in

Amps, rms Number of operation Amps, rms Number of operation

500 10,000 500 10,000

630 10,000 630 10,000

1,000 10,000 1,000 10,000

1,250 10,000 1,250 10,000

2,000 10,000 2,000 3,600

3,000 5,000 3,000 1,600

4,000 2,100 4,000 900

5,000 1,000 5,000 576

6,000 500 6,000 400

8,000 155 8,000 225

10,000 99 10,000 144

12,000 69

Check the condition of contact of vacuum interrupter on the display of control box through “CONDITION VERIFY” of diagnostics function.

If existent capacity of the contact becomes less than 20%, the replacement of the vacuum interrupters is required and maintenance personnel should contact manufacturer for the replacement.


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Auto Recloser Inspection Report Inspection Type: Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site Auto recloser ID

Type Rating

Plant of

Manufacture Serial Number Year of Manufacture


External physical conditions

Gas Pressure condition Recloser

Operating test

External physical conditions

Internal conditions

Operating test

Contact condition %

Type Primary Secondary

Main V V

Control

Box

Battery

test

Polarr Relay V V

Remark

• Number of operating counter before inspection on the control box:

• Number of operating counter after inspection on the control box:



Date : Date :


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Polarr Relay Settings Unit Requirements Input Chart System Settings

Number of Trips Dead Time(s) Secs Reclaim Time(Secs)

Phase Sequence 1st CT Ratio 100/200/300//1

Earth Sequence 2nd Seq Coordination IN/OUT

S.E.F. sequence 3rd Cold Load Pickup IN/OUT

Phase Settings

Trip Number 1st 2nd 3rd 4th

Prot. Curve

Time Multiplier

Added Delay (Secs)

M.R.T. (Secs)

Inst Trip

Trip Delay

Earth Settings

Trip Number 1st 2nd 3rd 4th

Prot. Curve

Time Multiplier

Added Delay (Secs)

M.R.T. (Secs)

Inst Trip

Inst Delay (Secs)

S.E.F Trip Time


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High I Lockout Phase Earth

Active Trip No

Multi Min Trp

Added Delay (Secs)

One-Shot Phase Earth

Prot Curve

Time Multi.

Inst. Trip

Inst. Delay (Secs)

Cold Load Pickup Phase Phase

Port. Curve

Time Mult.

Inst. Trip

Inst. Delay (Secs)

Fault Level Percentage Setting

Phase % Iset = setting % X Ict

20% to 320% in steps of 20%

E/G % Iset = setting % X Ict


S.E.F. % Iset = setting% X Ict



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XVI. Ring Main Unit


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1. General

1.1 Description The RMU has a completely sealed system with a stainless steel tank containing all the live parts and switching functions. A sealed steel tank with constant atmospheric conditions ensures a high level of reliability as well as personnel safety and a virtually maintenance-free system. The RMU offers a choice of either a switch fuse combination or a circuit breaker with relay for protection of the transformer.

1.2 Type of RMU RMU units are separated into extensible type RMU and Non extensible type RMU.

The extendable type RMU for feeder is equipped with one ring switch for a feeder and one for transformer is equipped with one CB for the T-off circuit linked to a distribution transformer.

The non extensible type RMU is equipped with two ring switches for feeder and one CB for the T-off circuit linked to a distribution transformer.

Example of Extendable circuit breakers and switches

(CE2, CE6, SE6 by Merlin Gerin)

Example of Non extensible circuit breaker and switch

(CN2, SN6 by Merlin Gerin)


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1.3 Structure (Example: Model CN2/SN6 Type)

1. Facia

2. Operating handle (padlockable)

3. Auxiliary/Protection compartment

4. Test access key (within LV pilot box)

5. Data plate/pilot box

6. Main circuit label on pilot box

7. Transformer earth switch

8. Gas pressure indicator

9. Tripped on fault flag

10. Main selector lever


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1.4 Rating

Extensible Non-extensible Type

Item Ring switch T-off CB T-off CB

Number of way 2 way 1 switch 3 way 3 switch

Rated voltage (kV) 12kV

Rated current (A) 1

Rated frequency (Hz) 50Hz

Rated short-time current (kA) 16

Rated peak withstand current (kA) 40

Power frequency withstand voltage 28

Impulse withstand voltage 75

Rated line-charging breaking

current (A) 1

Rated cable-charging breaking

current (A) 10

Insulating medium SF6 Gas

Installation type Indoor and outdoor

1.5 Protection system The RTU uses two types of protection system to protect the transformer: a switch fuse combination and a vacuum circuit-breaker.

In case of a switch fuse combination, the transformer will be protected by current-limiting HV fuses in combination with a load break switch. The load break switch is equipped with a stored spring energy mechanism which can be tripped by the fuse striker pin.

On the other hands, if using a vacuum circuit breaker, the transformer will be protected by a vacuum circuit breaker combined with relays and current transformers. The standard relays are based on digital technology and do not require an external power supply.


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2.1 Delivery RMU is shipped without covers closed and bolted, and with temporary shrouds over projecting through bushings.

To lift the RMU, use the crane on the top of the RMU, and lift with ropes or something similar. Failure to do so may result in variation or malfunction. Move the RMU on the flat place. Failure to do so may result in variation or malfunction. When placing the RMU on the ground, be careful not to drop or to impact the RMU. Failure to do so may result in variation or malfunction.

2.2 Storage Outdoor RMU can be stored for short periods provided that all apparatus are covered. Unit shall not be considered weatherproof until the paint work has been inspected and if necessary and damage shall be retouched. If the unit is to be stored for long periods a dry well ventilated area shall be provided. (If the unit has to be stored outside the chambers shall be filled with oil.) Covers shall be left closed to minimize breathing – especially in situations with wide daily temperature changes.

Indoor RMU must not be left outdoors. They shall be stored in a warm, dry, switch room and protected against dust and debris.

3. Inspection

3.1 Field inspection before operation Perform the following inspections after installing the RMU and before applying the current.

(a) Check the electrical wires and bus bars are fastened securely to the external line connection main terminal.

(b) Check any conductive foreign objects, such as screws, nails, processing chips from the panel and also connecting lead wires for the withstand voltage tests, are left around the terminals

(c) Check the front cover, base, etc is cracked or damaged.


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(d) Check the RMU has been flooded or there is condensation of dew.

(e) Examine the exterior of the unit for oil or compound leaks.

(f) Check the correct fuse-links are fitted.

(g) Check the gas pressure is adequate (normal minimum commissioning pressure is indicated on the green pressure range).

(h) Conduct a full sequence of operations to ensure proper working order.

3.2 Routine inspection All components within the SF6 insulated tank are maintenance free for the life expectancy of the unit. The tank is made of stainless steel. Scratches or other damage to panels must be repaired. Mechanical parts located outside the sealed tank are surface treated or made of corrosion resistant materials. These parts are lubricated during manufacture for the unit’s life expectancy. Units installed in extreme conditions are likely to require inspection depending on the nature of the environment. Where an outdoor enclosure is used, this shall be checked periodically for scratches or corrosion and the base of the stand must be kept clear of vegetation and well ventilated.


It is recommended that routine inspections are periodically performed every 3-years according to the guidelines for inspection to ensure a stable, long-term use of the RMU.


3.2.2.1 External appearance of the RMU

Inspection Item Inspection Method Criteria Treatment Method

Dust and soiling Visual inspection

There must be no

detrimental deposits of

dust and dirt.

Blow with air upon each

periodic inspection or

clean and remove the dust

with a dry cloth

Loosening of the

main circuit terminals

Tighten with a torque

wrench

Tightening torque in

correspondence with Retighten if necessary


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manufacturer’s instructions

Flooding, Immersion

in water

There must be no flooding

or immersion

There must be no

flooding or immersion

Replace the product if

flooding or immersion

has occurred

Loosening of the

Control terminals

Tighten with a screw

driver

Must be tightened

securely Retighten if necessary

Cracks, breakage or

Deformation

of the front cover,

base, control circuit

terminal black

Visual inspection

There must be no

cracks, breakage or

deformation

Replace the parts if there

are any abnormalities on

the front cover or the

control circuit terminal

block

3.2.2.2 Conductive part of the main circuit


Discoloration of the

moving and fixed

conductors

Visual inspection There must be no

Detrimental discoloration.

Replace the RMU if

there is any detrimental

discoloration

Soiling of the main

circuit conductors Visual inspection

There must be no

detrimental deposits of

dust or soot

Put methyl alcohol on a

cloth, etc and wipe.

Discoloration and

deformation of the

main circuit junction

Visual inspection

There must be no

discoloration of the

junction or deformation

of the flat spring

Replace the RMU if

there are any

abnormalities


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3.2.2.3 Switching mechanism part


Manual charge

operation of closing

spring

Manual operation

Must be able to perform

the charge operation

smoothly

Repair or replace the

RMU

if there are any

abnormalities

3.2.2.4 SF6 GAS


Leakage of SF6 Gas pressure gauge Indication shall be

on the green pressure range

Contact local

manufacturer’s office

4. Gas sampling and filling The gas density gauge on the front of the unit shows the density of SF6 gas in the unit. All units are tested to ensure that any leakage rate is so low as to give service life (about a thirty-year). During switching, the arc formed will cause the gas to dissociate. Once the arc is extinguished the SF6 reforms. A molecular sieve is fitted inside the switching enclosure to absorb any remaining ion products. When samples are required these are taken through the fitting of the gas density gauge on the front of the unit in the fuse compartment. Therefore, the fused switch must be switched to the earth position and the selector placed in the blocked position. The sample must be taken with the sampling kit available from manufacturer. This will ensure that any gas escaping during the sampling process is minimized. Gas is added through the same connection used to take samples. The filling adaptor of manufacturer allows the pressure inside the switch to be monitored during filling. Full details are included with the filling adaptor.


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Ring Main Unit Routine Inspection Report Inspection Date: 200 . . . Whether & Temperature: , ºC

Installation Site RMU ID

Voltage Load Current Type


Inspection Item Inspection result Remark

Dust and soiling

Loosening of the

main circuit terminals

Flooding, Immersion

in water

Loosening of the

Control terminals

External

appearance

Cracks, breakage or

Deformation

Discoloration of the

moving and fixed conductors

Soiling of the main

circuit conductors Conductive part

of the main circuit Discoloration and

deformation of the

main circuit junction

Switching

mechanism part

Manual charge

operation of closing

spring

SF6 GAS Leakage of SF6



Date : Date :


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XVII. Distribution Box,LV Panel, Pillar Box, Fuse Box


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1. General

1.1 Description

1.1.1 Distribution box and LV panel

An electric distribution box (LV panel) serves for the distribution of two phases, or of two phases and an earth and has a back member which receives, according to choice, two mounts which are each appropriate to the respective method of current distribution, these mounts comprising selector means which only permit couplings with compatible current connector plugs.

1.1.2 Pillar box

Pillar box is a metal box set into a wall to hold switches, receptacles, or similar electrical wiring components.

1.1.3 Fuse box

An electric fuse box is a box containing the switches and fuses (usually encased in a small glass or ceramic tube with metal ends) which lead into an electrical system serving eg. a whole building or part of it.


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1.2 Rating

1.2.1 Distribution box

Secondary current (A) MCCB rating (A) Rating capacity (kVA) Single-phase Three-phase Single-phase Three-phase

25 109 - 100 -

50 217 72 200 80

75 326 108 315 100

100 435 144 400 160

200 - 289 - 315

300 - 433 - 400

Table 26 MCCB rating of overhead transformer

1.2.2 Low voltage panel

MCCB rating (A) Transformer rating (kVA) Main Branch

300 1×400 1×400

500 1×800 2×400

750 1×1600 4×400

1000 1×1600 4×400 or 6×400

1500 1×1600 and 1×800 4×400 and 2×400

2000 2×1×1600 2×4×400

Table 27 MCCB rating of low voltage panel

1.2.3 Pillar box

Category Rated capacity (A) Cable size

Removable rink - 3.5C×240mm2


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80 4C×25mm2

100 3.5C×35mm2

160 3.5C×70mm2 Second MCCB

200 3.5C×95mm2

Table 28 MCCB rating of pillar box

1.2.4 Fuse box

Size of fuse-holder

Rated current of fuse-link

Size of fuse-holder


Size of fuse-

holder


16 A

20 A

25 A

32 A

40 A

50 A

63 A

80 A 80 A

100 A 100 A

125 A 125 A

160 A 160 A

200 A 200 A

250 A 250 A

315 A

Size 00 (160 A)

Size 1 (250 A)

Size 2 (400 A)

400 A

Table 29 Fuses capacity of fuse box


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2. Inspection

2.1 Daily inspection The daily inspection of distribution box, low voltage box, pillar box, fuse box shall be performed at the same time as patrol.

This inspection shall be carried out focusing on visual check such as locking condition of door, proper fuse use, condition and any damage, ventilation, evidence of overheating, strange sounding, signs of vermin, general cleanliness.


2.2.1 Inspection interval

The routine inspection of distribution box, low voltage box, pillar box, fuse box shall be performed annually.


(1) Check switchboard for;

- Condition and any damage.

- Ventilation.

- Evidence of overheating.

- Audible discharge.

- Signs of vermin.

- Combustible materials.

- General cleanliness.

(2) Insulation (if necessary)

- Check condition of all insulation, especially for, damage, cracks, signs of tracking or blistering and any defects.


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- Undertake thermal tests on boards with full loads.

- Conduct resistance tests with 500 volt insulation meter where power can be isolated without disruption to the site.

(3) Contactors

- Check operation of all contactors, if applicable.

(4) Contacts

- Check condition of contacts especially for pitting or damage.

- Check operation of contacts, especially backing springs pressure, contact and alignment, if applicable.

(5) Arc control devices

- Clean and check condition of arc shields and phase barriers.

(6) Mechanisms

- Clean and check condition and operation of ;

Mechanisms, especially rolling or sliding surfaces in trip mechanism

- All auxiliary contacts, if applicable.

(7) Connection s and cable terminations

- Check all main electrical connections;

for signs of overheating or verdigris.

are tight and making good contact.

- Use heat sensitive detector to locate any hot spots or joints.

- Check main earthing for continuity and mechanical protection.

- Check integrity of main earth electrode.

- Check integrity of main earth conductor.

- Check size of main earth conductor for compliance.


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- Measure current in main earth conductor, record in logbook.

- Measure neutral current, record in logbook.

(8) Auxiliary equipment

- Check condition and operation of auxiliary equipment, if applicable.

(9) Busbars

- Check condition of busbars, especially for; Discolouration from heating Damaged insulation Deformation Adequate support

- Check all neutral bars or links.

(10) Fuses, circuit breakers, switches and switch units

- Check condition, operation and correct rating.

(11) Other maintenance and inspection

- Check that all wiring duct covers are fitted.

- Check all equipment for security of mounting.


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XVIII. Diesel Generator


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1. General Diesel generators are used to maintain the voltage within prescribed limits on the LV network during emergency and maintenance periods, provide temporary supply to isolated sections of the distribution network, and supply load which cannot be held in LV parallel.

1.1 Structure Refer to figure 1. The major components of the generator are clearly shown. Stationary or mobile units are available with each package including an alternator, diesel engine, exhaust, cooling system, and a control system.


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Figure 30 Typical generator set configuration

No. Name No. Name

1 Diesel engine 8 Bellows

2 Alternator 9 Bed frame

3 Fan 10 Load terminal

4 Control Panel 11 Air cleaner

5 Radiator 12 Fuel filter

6 Terminal box

7 Turbo Charger

1.2 Instruction (a) Manufacturers provide specific instructions for the use and care of each of their

products. Their instructions are the result of wide experience obtained under varying conditions and should be followed closely. Maintenance personnel should always check equipment first for signs of physical damage before performing any other checks.

(b) Routine maintenance instructions consist of scheduled inspections of engines, generators and exciters, and switchgear. When a need for service or repair is indicated, refer to the manufacturer’s literature for specific information. Service records of the auxiliary power systems are filed in the maintenance’s engineering office.

(c) Maintenance information provided in this manual supplements the manufacturer’s instructions but does not supersede them. Checklists and schedules furnished herein are intended as guides for operators and service personnel.

(d) Electrical systems acceptance tests are functional tests to verify the proper interaction on all sensing, processing, and action electrical devices. It is critical that these tests be performed on standby generator power systems to ascertain the safe and operational reliability of a system. A system must be tested as a united series of devices in addition to the testing of individual components. For systems that include auto-start, auto-transfer, and/or auto-synchronizing equipment, every six months utility electrical power should be removed (open main circuit breaker) from part of the facility that is supplied electrical power by commercial power/generation combination to ascertain that the system will operate under abnormal conditions.


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1.3 Consideration

1.3.1 Mechanical safety considerations

(a) Do not attempt to operate the generator set with safety guards removed, while the generator set is running do not attempt to reach under of ground the guards to do maintenance or for any other reason.

(b) Keep hands, arms, long hair, loose clothing and jewelry away from pulley, belts and other moving parts.

(c) Some moving parts can not be seen clearly when the set is running.

(d) Keep access doors on enclosures, if equipped, closed and locked when not required to be open.

(e) Avoid contact with hot coolant, hot exhaust gases, hot surfaces, and sharp edges and corners.

(f) Wear protective clothing including groves and hat when working around the generator set.

(g) Do not remove the radiator filler cap until the coolant has cooled. Then loosen the cap slowly to relieve any excess pressure before removing the cap completely.

1.3.2 Chemical safety considerations

Fuels, oils, coolants, lubricants and battery electrolyte used in generator set are typical of the industry. However they can be hazardous to personnel if not treated properly.

(a) Do not swallow skin contact with fuel, oil, coolant, lubricants or battery electrolyte. If swallowed, seek medical treatment immediately. Do not induce vomiting soap and water.

(b) Do not wear clothing that has been contaminated by fuel or lube oil.

(c) Wear an acid resist apron and face shield or goggles when serving the battery. If electrolyte is spilled on skin or clothing, flush immediately with large quantities of water.


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1.3.3 Noise safety considerations

Generator sets that are not equipped with sound attenuating enclosures can produce noise levels of 1005dBA. Prolonged exposure to noise level above 5dBA is hazardous to hearing.

(a) Ear protection must be worn when operating or working around an operating generator set.

1.3.4 Electric safety considerations

Safe and efficient operation of electrical equipment can be achieved only if the equipment is correctly installed, operated and maintained.

(a) The generator set must be connected to the load only by trained and qualified electricians who are authorized to do so, and in compliance with relevant electrical codes, standards, and other regulations. Where required, their work should be inspected and accepted by the inspection agency prior to operating the generator set.

(b) Ensure the generator set is effectively grounded/earthed in accordance with all relevant regulation prior to operation.

(c) Generator set should be shutdown with the battery negative (-) terminal disconnected prior to attempting to connect or disconnect load connection.

(d) Do not attempt to connect or disconnect load connections while standing in water or on wet soggy ground.

(e) Do not touch electrically energized parts of the generator set and/or interconnecting cables or conductors with any part of the body or with any non insulated conductive object.

(f) Replace the generator set terminal box cover as soon as connection or disconnect of the load cables is complete when it is worn or damaged. Do not operate the generator set without the cover securely in place.

(g) Make sure the bolt securing the load line to the terminal is not loosened or released. Keep the bolt tight at all times.

(h) Connect the generator set only to load and/or electrical systems that are compatible with its electrical characteristics and that are within its rated capacity.

(i) Be sure all electrical power is disconnected from electrical equipment being served.

(j) Keep all electrical equipment clean and dry. Replace any wiring where the insulation


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is cracked, cut, abraded or otherwise degraded or corroded. Keep terminals clean and tight.

(k) Insulate all connections and disconnected wires.

2. Delivery and handling Do not lift generator set by the lifting eyes attached to the engines and/or alternator. These lifting eyes are only used during generator assembly and are not capable of supporting the entire weight of the generators. The mounting skid of each generator set includes four holes for attaching the lifting device. These holes are strategically placed to avoid damage to generator components by lifting cables and to maintain balance during lifting. In some cased, it may be necessary to remove protruding generator components (air cleaner) to avoid damage by lifting cables.

A four-point lifting method is necessary to lift the generator set.

To maintain generators balance during lifting, the lifting apparatus must utilize the four skid lifting holes mentioned in the previous paragraph. One method of lifting generators uses and apparatus of hooks and cables joined at a single rigging point. The use of spreader bars is necessary with this method to avoid damage to the set during the lifting procedure.

The spreader bars should be slightly wider than the generator skid so the set is not damaged by lifting cables and only vertical force is applied to the skid while lifting. The generator sets may also be lifted by placing bars through the skid lifting holes and attaching hooks to the ends of the bars.

In all cases, be sure the components of the lifting device (cables, chains, bars) are properly sized for the weight of the generator set.

3. Inspection

3.1 Weekly inspection If generator set is used as emergency equipment or used around once a week, you must check up by running the generator set once a week at least. The table 1 shows the summary of daily maintenance. For details, refer to the manufacturer’s specific instructions.


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Table 30 Weekly maintenance or at each start up

No Check point Result Remedy

1 Generator Set Potential leaks from the engine fuel system cooling

system or lubrication leaks Tighten

Obstructions in the cooling air ventilation screens 2 Alternator

Heavy accumulation of dust and dirt

3 Control panel Heavy accumulation of dust and dirt

Clean any heavy

accumulations

4 Air cleaner

element Heavy accumulation of dust and dirt Replace if necessary

5 Fuel gauge Fuel level Replenish if necessary

Engine coolant level

Radiator cap condition Replenish

6 Radiator

Obstructions of air flow

7 Fan Rotation condition

8 Belts Tension condition

9 Hoses Connection condition

Tighten or replace if

necessary

10 Oil level Engine oil level and condition Replenish if necessary

Terminals for corrosion Removal

Electrolyte level Fill with distilled water

if necessary 11 Battery

Voltage level Recharging

12 Engine Specific engine maintenance requirements Refer to the engine

maintenance manual

Start the generator set after all checks have been made

13 Exhaust system Exhaust gas leakage Tighten

14 Noise or

vibration Any abnormal condition

Fluid leakage 15 Generator set

High temperature

16 Items Dispose of any unnecessary items in the vicinity of

the generator set Clean if necessary

17 Control panel Indications of abnormal operation Refer to service manual


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3.2 Routine inspection Routine inspection of diesel generator set should be made every 6-months or 250 hours.

(a) Repeat the daily requirements.

(b) Check all safety devices by electrically simulating a fault to ensure that all system will function properly in the event of a fault

(c) Clean all battery cap vents.

(d) Start the generator set and observe the control panel to be sure that all gauges and meters are operating property.

(e) Tighten all exhaust connections.

(f) Tighten all electrical connection

(g) Refer to the engine maintenance manual of manufacturer for further details.

3.2.1 Cooling water

(a) Check the cooling water level by opening the filler cap on the top of the radiator or by reading the gauge level on the top of radiator, and cooling water if necessary.

(b) Replace the radiator filler cap if it is damaged or the joint is loose.

3.2.2 Fan belt

(a) Use a fan belt of specified dimension and replace if damaged, frayed, or deteriorated.

(b) Check the fan belt tension. If belt tension is lower than the specified limit, adjust the tension by relocating the charging alternator and idle pulley. (Specified deflection: 10-15mm when pressed down with thumb)

3.2.3 Engine oil

(a) Check oil level using the oil dip stick and replenish if necessary.

(b) Check the oil level on a level ground, engine cooled. The oil level must be between MAX and MIN lines on the stick.

(c) Engine oil should be changed every 250 hours. Oil in the oil filter also should be changed simultaneously.


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3.2.4 Oil filter

(a) Check for oil pressure and oil leak, and repair or replace the oil filter if necessary.

(b) Replace the oil filter element should be replaced every 500 hours operation.

3.2.5 Air cleaner

(a) Damaged air cleaners should immediately be replaced.

(b) Clean or replace the element periodically.

3.2.6 Battery

(a) Check the battery for damage or leaking of battery fluid (electrolyte) from cracks on the battery. Replace the battery if damaged.

(b) Check battery fluid level and add distilled water if necessary.

(c) Measure the specific gravity of the electrolyte in the battery. Recharge the battery if the hydrometer readings are lower than the specified limit.

(d) If the DC volt meter of the control panel indicates a value less than a reference. Check up and recharge batteries.


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Table 31 Periodic inspections and determination of maintenance term

Items of maintenance Setting Daily 10 -

20Hr

100

Hr

200

Hr

400

Hr

1000

Hr

Leakage Check Ο

Fastening Check Ο

Mounting Check Ο

Valve Clearance Check Ο Ο

Compression pressure Check Ο

Engine

State of exhaust gas Check Ο

Injection nozzle pressure &

spray pattems Check Ο

Fuel level Check Ο

Fuel filter element Replace Ο

Fuel strainer Clean Ο

Fuel system

Fuel filter Replace Ο

Oil level Check Ο

Oil filter element Replace Ο Ο Lub.

system Oil strainer Clean Ο

Engine oil Change Ο

Lub. System Supply Ο Lub.

Oil Bearing grease Supply Ο

Belt tension Check Deflection:

10mm(’) Ο Cooling

system Cooling water level Check Ο

Intake air

system Air cleaner Check Ο

Battery electrolyte capacity Check Ο

Battery gravity Check Ο

DC charging alternator Check Ο

Starter Check Ο

Electric

system

Wire connection Check Ο

1) The 10-20 Hr column is only applied to new engine or the overhauled. 2) For the generator set used for an emergency, the engine oil should be replaced twice a year at least (in spring and autumn) 3) “” : initial 4) To carry out maintenance and trouble shooting engine should be stopped in cold condition. 5) (’) : When pressed down with thumb.


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Diesel Generator Routine Inspection Report Inspection Date: 200 . . . Whether & Temperature: , ºC

Items of maintenance Setting Result Remark

Leakage Check

Fastening Check

Mounting Check

Valve Clearance Check

Compression pressure Check

Engine

State of exhaust gas Check

Injection nozzle pressure

& spray pattems Check

Fuel level Check

Fuel filter element Replace

Fuel strainer Clean

Fuel

system

Fuel filter Replace

Oil level Check

Oil filter element Replace Lub.

system Oil strainer Clean

Engine oil Change

Lub. System Supply Lub.

Oil Bearing grease Supply

Belt tension Check Deflection:

10mm Cooling

system Cooling water level Check

Intake

air

system

Air cleaner Check

Battery electrolyte capacity Check

Battery gravity Check

DC charging alternator Check

Starter Check

Electric

system

Wire connection Check




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XIX. Public Lightning


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1. General

1.1 Description Outdoor lighting includes public way, recreational, airfield, and security or protective lighting, whether installed on buildings or detached supports. The primary purpose of outdoor lighting is to provide lighting for exterior facilities, which require some degree of lighting during times of reduced visibility for safety or for observation.

1.2 Types of public lighting circuits Most lighting circuits GECOL uses will be of the multiple circuit type. Generally series circuits are used for only airfield lighting systems (except for very small airfields) to provide uniform brightness to all lights in a circuit.

1.3 Multiple type lighting system components A multiple type lighting system consists of luminaires, mounting structures for luminaires, the control system to switch luminaires on and off, and the input circuit which provides the low voltage to operate the luminaires.

1.4 Luminaires The basic, most visible part of an exterior lighting system is the combination of luminaire and lamp or lamp/ballast. All gaseous conductor lamps require ballasts. A bare lamp at the end of a pair of wires will emit light, perhaps in large amounts, but only a part will be directed to where it will be useful and the rest is wasted. Luminaires are used to direct the light where it is wanted and, if necessary, to house the ballast.

1.5 Lamp types There are two types of lights used in outdoor luminaires. These are filament types and gaseous conductive types. Filament lamps use the filament for conducting current. Gaseous conductive types use an ionized gas or vapor for the electron flow and are of the electric-discharge lamp type or fluorescent lamp type. GECOL uses the electric-discharge lamp


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among the gaseous conductive type lamps for public lighting.

1.5.1 Electric-discharge lamps

Electric or gaseous discharge lamps include mercury-vapor, metal-halide, and high- and low-pressure sodium lamps. They differ in the gas or vapor used, which is either mercury, or mercury with halide salts, or sodium, at different pressures. Most outdoor public way lighting installations today use high-pressure sodium lamps. Most older mercury vapor luminaires are being replaced with high-pressure sodium luminaries because of the energy savings. Metal-halide lamps may be used for recreational and protective lighting systems, because their superior color rendition outweighs their lower lamp life and lumen output. Low-pressure sodium lamps, though they have a greater lumen output, also have a monochromatic color rendition and a lower lamp life and are rarely used for outdoor lighting installations on military facilities. All lamps require ballasts for correct operation.

1.5.2 Fluorescent lamps

A fluorescent lamp utilizes a mercury vapor, but the inside of the bulb has a thin coating of phosphor which glows or fluoresces when struck by the electrons flowing through the mercury vapor. The amount of light emitted is less than for electric discharge lamps, and only a limited control is possible because of their tubular shape.

They may be used for lighted roadway, traffic, or airfield indication signs. All lamps require ballasts for correct operation, and some types require separate starters to provide the heat necessary for the electron emission to start.

1.6 Characteristics of lamps The characteristics of the each lamp are as follows.

1.6.1 High-pressure mercury vapor lamps

Nominal wattage 125W 250W 400W

Ratings Rated Min Max Rated Min Max Rated Min Max

Starting voltage (V) - - 180 - - 180 - - 180

Starting time (s) - - 10 - - 10 - - 10

Warm-up current (A) 1.04 - - 1.94 - - 2.93 - -


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Warm-up voltage (V) - 93 - - 98 - - 102 -

Warm-up time (s) - - 12 - - 12 - - 12

Wattage (W) 125 - 132 250 - 263 400 - 420

Terminal voltage (V) 125 110 140 130 115 145 135 120 150

Current (A) 1.15 - - 2.13 - - 3.25 - -

1.6.2 High-pressure sodium lamps



Wattage (W) 125 - 132 250 - 263 400 - -

Terminal voltage (V) 100 85 115 100 85 115 105 90 120

Current (A) 1.8 - - 3 - - 4.45 - -

Extinguishing voltage (V) 116 - - 120 - - 125 - -

1.6.3 Metal-halide lamps



Starting voltage (V) 95 85 105 100 90 110

Starting time (s)

Warm-up current (A)

Warm-up voltage (V) 1.8 3.2

Warm-up time (s) 180 360

Wattage (W) 146 250

Terminal voltage (V) 220

Current (A)

Extinguishing voltage (V)

1.7 Luminaire components In addition to lamp or lamp/ballast combination, the components of a luminaire include its optical controls, its component support assembly.


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1.7.1 Optical controls

Optical controls are used to provide the light distribution pattern most appropriate to the outdoor lighting requirement. One type of control is a reflector which uses a parabolic, ellipsoidal, or hyperbolic contoured surface with a specular, spread, diffuse, or compound finish to redirect light from a lamp into the desired pattern.

Another type of control is a refractor which uses a different medium to bend the light. Refractors can provide a variety of light distributions, using prismatic or lens type refractors of glass or plastic. Other optical control methods use glass or plastic materials to scatter light or control brightness. Louvers or shields are used to mask a source or to absorb unwanted light. Any degradation of these items resulting from accumulated dirt or fixture damage will result in a less efficient lighting installation.

1.7.2 Component support assembly

The assembly provides the mechanical support for lampholders, sockets, ballasts, controls, reflectors, refractors, enclosures, mounting components, and other items needed to ensure the lamp provides the performance needed.

1.8 Multiple type lighting controls Most control is provided by either a central control or an integral control. Central controls use a time switch with an astronomical dial, or a contactor controlled by a photo cell. Integral systems have a photo cell installed on each luminaire. GECOL uses central controls for lighting control.

2. Inspection

2.1 Interval of inspection The design footcandle level is generally the average illumination delivered at the design point when the illuminating source is at its lowest output and the luminaire is in its dirtiest condition. This requirement determines the maintenance interval.

2.1.1 Lamp depreciation


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The lumen output of HPS lamps will decrease to 80 percent of its initial value at about 80 percent of its rated life. The lamp shall then be replaced to maintain design footcandle levels. Rated lamp life is defined as approximately the time for half of the lamps to fail. Using a value of 24,000 hours for 80 percent of lamp life, and 4,000 hours of burning time per year, results in a theoretical 6-year life for half the lamps.

On this basis, consider group replacement every 4 years. Premature outages can probably be held to approximately 10 percent if group replacement is made before the lamps approach the accelerated point on their mortality curve. The few lamps which do fail shall be replaced promptly.

2.1.2 Luminaire depreciation

Dirt on lamps, reflectors, and refractors is another cause of decreased lumen output. A cleaning schedule shall be set up on an annual basis, that under normal operating conditions, dirt will not contribute more than 15 percent to the lighting depreciation. Cleaning recommendations for average dirt conditions range from every 2 to 3 months up to a 2-year schedule for inspection, cleaning, and washing.

2.1.3 Time switches

Time switches shall be checked monthly and reset and adjusted if necessary. The contacts shall be checked about once a year in the process of inspecting their time switches..

2.2 Inspection method

2.2.1 Luminaire

Luminaire maintenance given herein is for high-pressure sodium (HPS) lamps which will most often be found in roadway and recreational lighting. Maintenance of other lamps shall follow the same philosophy. Luminaire maintenance consists of cleaning, lamp replacement, and troubleshooting of components when other problems are indicated.

2.2.1.1 Cleaning

Cleaning can be done from lift trucks using a one- or two-man crew. The crew shall be familiar with the necessary cleaning steps and the appropriate cleaning compounds for the


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application.

(1) Procedure

The cleaning sequence will vary dependent upon the type of luminaire, but typical methods for streetlights can be modified for other types of fixtures.

(a) Remove any removable shielding material and the lamp.

(b) Make the luminaire shock-free. Ensure that the electrical circuit is turned off or make the luminaire shock-free by covering sockets with tape or dummy lamp bases.

(c) Clean the basic unit. If required, heavy deposits of dirt can be removed first from the luminaire’s top surface by wiping or brushing. Reflective or refractive surfaces are better off not wiped but only washed.

(d) Clean the shielding material and lamps. Plastic materials shall be allowed to drip dry after rinsing or be damp dried with toweling or some other material. Dry wiping can cause the formation of electrostatic charges. New lamps shall be dry wiped before installation.

(e) Replacement may require installing new shielding and new lamps.

(2) Cleaning compounds

Washing solutions shall always be in accordance with the luminaire manufacturer’s instructions. Strong alkaline or abrasive cleaners shall be avoided. Most luminaire finishes can be cleaned using the following procedures.

(a) Aluminum

Very mild soaps and cleaners can be used on aluminum and will not affect the finish, if the material is thoroughly rinsed with clean water immediately after cleaning. Strong alkaline cleaners shall never be used.

(b) Porcelain enamel

This finish is not injured by nonabrasive cleaners. Detergents and most automobile and glass cleaners do a good job under average conditions.

(c) Synthetic enamel

Some strong cleaners may injure this finish, particularly if the enamel is left to soak in the solution. Alcohol or abrasive cleaners shall not be used. Detergents produce no harmful


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effects.

(d) Glass

As with porcelain enamel, most nonabrasive cleaners can be used satisfactorily on glass. Dry cleaners are usually preferred on clear glass panels, but not on etched or sand blasted surfaces. Most detergents will work well under average conditions.

(e) Plastics

Dust is very often attracted by the static charge developed on plastic. Most common detergents do not provide a high degree of permanence in their anti-static protection. In most areas, however, if the plastic is cleaned at least twice a year with a detergent, a satisfactory balance. in regard to static dirt collection is obtained.

2.2.1.2 Troubleshooting

The main defects requiring maintenance are nonstart, cycle on and off, extra bright light output, and low light output. Some of these conditions result from normal end of lamp or ballast life. Other conditions result from loose wiring, ballasts, or lamps, or from incorrect lamp and ballast installations. Refer to the manufacturers’ lamp, ballast, and luminaire troubleshooting guides. Ballast replacement and voltage and current measurements present the possibility of exposure to potentially hazardous voltages and shall be performed only by qualified personnel.

2.2.1.3 Replacement

Consider replacing glass items with tougher materials such as acrylics if breakage (vandalism) becomes a problem. Replace incandescent lamps with discharge lamps (sodium preferred) whenever possible. Departmental policy shall be complied with in changing lamp types.

2.2.2 Time switches

Time switches used on lighting circuits shall have an astronomical dial, which ideally has been adjusted at the factory for the particular locality in which it is used. If it is necessary to do so in the field, adjust as follows:

(a) See that the center dial screw is tight.

(b) Turn the dial either by the manual reset knob or by the dial screws in the direction


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indicated by the arrow until the correct time of day is directly under the hour pointer. The black half-moon represents night periods.

(c) Turn the star wheel in either direction until the date pointer is directly over the correct day and month. Spring-driven mechanisms may gain or lose time because of temperature variations. Synchronous motor-driven clocks will lose time if there is an interruption to service. The contacts shall be checked about once a year. Contacts shall be inspected and replaced if badly pitted. The clock mechanism shall be overhauled every 5 years by the manufacturer or a competent watchmaker.


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Public Lighting Maintenance Report

Maintenance Date: 200 . . . Whether & Temperature: , ºC

Lamp Location

Mercury Sodium Metal-halideBallast Luminaires Stadium

lamp GardenLamp

LampHolder Starter Connection Wire Remark

125 250 400 250 400 150 250 125 250 400



Documents

GOM 07. Guideline for Inspection of GECOL Equipments