TECHNICAL REPORT

Topic: 132 kv Substation Bosan Road Multan

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Complete layout of 132 kv Substation Bosan road Multan. Description of equipment used in Substation and outgoing of Substation.

Group members

Talha Maqsood 2008-EE-29 Ali yasir noor 2008-EE-31Ali Raza 2008-EE-01Sultan Zeb 2008-EE-55

Submitted To

Engr.Tuheed-ur-Rehman

Contents1.1 Introduction---------------------------------------------------------------------------04

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1.2 Brief history of electric power-----------------------------------------------------041.3 Electrical power system------------------------------------------------------------051.4 Electrical distribution --------------------------------------------------------------05 1.4.1 AC distribution-----------------------------------------------------------061.5 Definition of sub-station-----------------------------------------------------------06 1.5.1 Classification of sub-station--------------------------------------------061.6 Functions of a substation-----------------------------------------------------------071.7 132KV Substation Bosan Road Multan------------------------------------------081.8 Equipment used in a sub-station--------------------------------------------------09

1.8.1 Bus – bar-------------------------------------------------------------------101.8.2 Insulators------------------------------------------------------------------111.8.3 Isolating switches--------------------------------------------------------111.8.4 Instrument transformer--------------------------------------------------12

1.8.4.1 Current transformer-----------------------------------------121.8.4.2 Voltage transformer-----------------------------------------13

1.8.5 Metering and indicating instrument ----------------------------------141.8.6 Miscellaneous equipment-----------------------------------------------151.8.7 Protective relay-----------------------------------------------------------151.8.8 Circuit breaker------------------------------------------------------------17

1.8.8.1 The type of the circuit breaker-----------------------------181.8.8.2 Breaker used in 132KV grid station----------------------191.8.8.2.1 Oil circuit breaker----------------------------------------191.8.8.2.2 Vacuum circuit breaker----------------------------------191.8.8.2.3 SF6 circuit breaker---------------------------------------20

1.8.9 Power transformer-------------------------------------------------------211.8.9.1 Parallel operation of three-phase transformers---------22

1.8.10 Bus-bar schemes used in a sub station------------------------------231.8.11 Bus-bar isolator---------------------------------------------------------231.8.12 Bus coupler--------------------------------------------------------------241.8.13 Battery -------------------------------------------------------------------24

1.8.13.1 Batteries room ---------------------------------------------251.8.14 Lighting arrestor--------------------------------------------------------251.8.15 Capacitor -----------------------------------------------------------------26

1.9 Outgoings -------------------------------------------------------------------------------27

1.1 IntroductionElectricity is the basic need for the economic development of any country. Electricity has now become a necessity for all as it powers the machinery, the computers, the health-care systems and the entertainment of modern society. Every power system has three major components

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Generation: source of power, ideally with a specified voltage and Frequency. Transmission system: transmits power; ideally as a perfect conductor. Load: consumes power; ideally with a constant resistive value.

1.2 BRIEF HISTORY OF ELECTRIC POWER

Early 1880’s – Edison introduced Pearl Street dc system in Manhattan supplying 59 customers

1884 – Sprague produces practical dc motor 1885 – invention of transformer Mid 1880’s – Westinghouse/Tesla introduce rival ac system Late 1880’s – Tesla invents ac induction motor 1893 – First 3 phase transmission line operating at 2.3 kV 1896 – ac lines deliver electricity from hydro generation at Niagara Falls to Buffalo,

20 miles away. Early 1900’s – Private utilities supply all customers in area (city); recognized as a

natural monopoly; states step in to begin regulation By 1920’s – Large interstate holding companies control most electricity systems 1935 – Congress passes Public Utility Holding Company Act to establish national

regulation, breaking up large interstate utilities 1935/6 – Rural Electrification Act brought electricity to rural areas.

1.3 ELECTRICAL POWER SYSTEM

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1) The generating station converts the energy of gas, oil, coal or nuclear fuel to electric energy. The generator voltage is around 15-25 kV (12.5KV at Mangla Dam Generation).

2) The main transformer increases the voltage to 230-765 kV. (220-500KV in Pakistan) This reduces the current and losses.

3) The high voltage transmission line transports the energy from the generating station to the large loads, like towns. Example: Energy generated at Palo Verde is transported by a 500 kV line to the KYRENE substation at Phoenix.

4) The high voltage substation reduces the voltage to 500-220 / (220-132) kV. The substation serves as a node point for several lines.

5) The sub-transmission lines (132 kV-11 kV) connect the high voltage substation to the local distribution station.

6) The Distribution lines 11 kV distribute the energy along streets or underground. Each line supplies several step-down transformers distributed along the line.

7) The distribution transformer reduces the voltage to 240 (1-phase) or 415V (3-phase) which supplies the houses, shopping centers, etc.

1.4 Electrical Distribution

There are two types of Electrical distribution1) AC Distribution2) DC Distribution

1.4.1 AC Distribution

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Now a days A.C. system is universally used for distribution of electric power as it is more economical than direct current method. One important reason for the use of alternating current in preference to direct current is the fact that alternating voltage level can be changed in magnitude by a transformer. High transmission and distribution voltages have greatly reduced the current in the conductors and the resulting line losses.

High voltage AC transmission offers Higher transmission capacity / Km Lower line-voltage drop / Km Lower transmission losses / MW transfer Reduced right-of-way requirement / MW transfer Lower capital and operating costs / MW transfer

The electric power is produce at the power station, which are located at favorable places, generally quite away from the consumers. It is delivered to the consumer through a large network of transmission and distribution. At many place in the line of power system, it may be desirable and necessary to change some characteristic (e.g. Voltage, AC to DC, frequency P.F. etc.) of electric supply. This is accomplished by suitable apparatus called sub-station for example, generation voltage (5kv or 20kv) at the power station is stepped up to high voltage (Say 500kv,220kv,132kv or 66kv) for transmission of electric power. Similarly near the consumer’s localities, the voltage may have to be stepped down to utilization level. This job is again accomplished by suitable apparatus called sub-station.

1.5 Definition of sub-station“The assembly of apparatus used to change some characteristics (e.g. Voltage

frequency. P.F. etc) of electric supply is called sub-station”.1.5.1 Classification of sub-station

There are several ways of classifying sub-station. However the two most important way of classification is

I) According to service requirementII) According to constructional features

1.5.2 According to service requirementAccording to service requirement sub-station may be classified into1) Transformer sub-station

Those sub-station which change the voltage level of electrical supply are called TIF .2) Switching sub-station These sub-station simply perform the switching operation of power line.3) Power factor correction These sub-station which improve the P.F. of the system are called P.F. correction, these are generally located at receiving end.4) Frequency changer Those sub-stations, which change the supply frequency, are known as frequency changer . Such may be required for industrial utilization.

5) Converting sub-station

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Those sub-station which change a.c. power into d.c. power are called converting. Ignition is used to convert AC to dc power for traction, electroplating, electrical welding etc.6) Industrial sub-station Those sub-stations, which supply power to individual industrial concerns, are known as industrial sub-station.

1.5.3 According to constructional featuresAccording to constructional features, the sub-station are classified as 1) Outdoor Sub-Station

For voltage beyond 66KV, equipment is invariably installed outdoor. It is because for such Voltage the clearances between conductor and the space required for switches, C.B. and other equipment becomes so great that it is not economical to installed the equipment indoor.2) Indoor Sub-station

For voltage up to 11KV, the equipment of the is installed indoor because of economic consideration. However, when the atmosphere is contaminated with impurities, these sub-stations can be erected for voltage up to 66KV.3) Under ground sub-station

In thickly populated areas, the space available for equipment and building is limited and the cost of the land is high. Under such situations, the sub-station is created underground.The design of underground s/s requires more careful consideration1) The size of the s/s should be as minimum as possible.2) There should be responsible access for both equipment & personal.3) There should be provision for emergency lighting and protection against fire.There should be good ventilation4) Pole-mounted sub-station

This is an outdoor sub-station with equipment installed overhead on H.pole or 4-pole structure. It is the cheapest from of s/s for voltage not exceeding 11KV(or 33KV in some cases). Electric power is almost distributed in localities through such sub-station.

The 11KV line is connected to the T/F (11KV/440V) through gang isolator and fuses. The lighting arresters are installed on the H.T. Side to protect the sub-station from lighting strokes. The transformer step down voltage to 400 V, 3 phase, 4 wire supply. The voltage between any two lines is 400 V & between line & neutral is 230V. The oil circuitt breaker installed on the L.T. side automatically isolates the mounted sub-station. transformers are generally in the event of fault generally 200KVA transformer is used.

1.6 Functions of a Substation

1 - Supply of required electrical power. 2 - Maximum possible coverage of the supply network. 3 - Maximum security of supply. 4 - Shortest possible fault-duration. 5 - Optimum efficiency of plants and the network. 6 - Supply of electrical power within targeted frequency limits, (49.5 Hz and 50.5 Hz). 7 - Supply of electrical power within specified voltage limits. 8 - Supply of electrical energy to the consumers at the lowest cost.

1.7 132KV Substation Bosan Road Multan

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132KV Substation Bosan Road Multan is an out-door substation. A simple layout of substation is shown below

Figure 1

Symbol used in DiagramIsolator

Current Transformer

Circuit Breaker

Potential Transformer

Power Transformer

Lighting Arrester

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Incoming Supply1) Industrial state side2) Khanewal side

1.8 Equipment Used in a Sub-StationThe equipment required for a transformer Sub-Station depends upon the type of Sub-Station, Service requirement and the degree of protection desired. 132KV Sub-Station Bosan Road Multan has the following major equipments.

1) Bus-bar2) Insulators3) Isolating Switches4) Circuit breaker5) Current transformer6) Power transformer

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7) Potential transformer8) Aux-transformer9) Lighting arrestor10) Capacitor bank11) Batteries 12) Bus coupler13) Relay room14) Metering and Indicating Instrument

1.8.1 Bus - barWhen a no. of lines operating at the same voltage have to be directly

connected electrically, bus-bar are used, it is made up of copper or aluminum bars (generally of rectangular X-Section) and operate at constant voltage.

Duplicate bus-bar, generally it consist of two bus-bars a “main” bus-bar and spare bus-bar. The incoming and outgoing lines can be connected to either b/b. With the help of a bus-bar coupler, which consist of a circuit breaker and isolators.

However, in case of repair of main bus-bar or fault accusing on it, the continuity of supply to the circuit can be maintain by transforming it to the spare bus-bar for voltage exceeding 33KV, Duplicate bus-bar is frequently used.Bus-bar scheme used in 132KV Substation Bosan Road Multan is single Bus bar scheme as can be seen in layout (Figure I).

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1.8.2 InsulatorsThe insulator serves two purpose. They support the conductor ( or bus bar )

and confine the current to the conductor. The most commonly used material for the manufactures of insulators is porcelain. There are several type of insulator (i.e. pine type, suspension type etc.) and there used in Sub-Station will depend upon the service requirement.

1.8.3 Isolating SwitchesIn Sub-Station, it is often desired to disconnect a part of the system for

general maintenance and repairs. This is accomplished by an isolating switch or isolator. An isolator is essentially a kniff Switch and is design to often open a ckt under no load, in other words, isolator Switches are operate only when the line is which they are connected carry no load. For example, consider that the isolator are connected on both side of a cut breaker, if the isolators are to be opened, the C.B. must be opened first.

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Insulators

1.8.4 Instrument TransformerThe line in Sub-Station operate at high voltage and carry current of thousands

of amperes. The measuring instrument and protective devices are designed for low voltage (generally 110V) and current (about 5A). Therefore, they will not work satisfactory if mounted directly on the power lines. This difficulty is overcome by installing Instrument transformer, on the power lines. There are two types of instrument transformer.

1) Current transformer2) Potential transformer3) Power transformer4) Aux-transformer

1.8.4.1 Current TransformerA current transformer is essentially a step-down transformer which steps-

down the current in a known ratio, the primary of this transformer consist of one or more turn of thick wire connected in series with the line, the secondary consist of thick wire connected in series with line having large number of turn of fine wire and provides for measuring instrument, and relay a current which is a constant faction of the current in the line.The current transformer (CT) is often treated as a ‘‘black box.’’ It is a transformer that is governed by the laws of electromagnetic induction:ε = k βAc NfWhere ε = Induced voltage β = Flux densityAc = Core cross-sectional areaN = Turnsf = Frequency k = Constant of proportionality

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CT 200/5A

1.8.4.2 Potential TransformerIt is essentially a step - down transformer and step down the voltage in

known ratio. The primary of these transformer consist of a large number of turn of fine wire connected across the line. The secondary way consist of a few turns and provides for measuring instruments and relay a voltage which is known fraction of the line voltage.

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CT 600/5A

1.8.5 Metering and Indicating InstrumentThere are several metering and indicating Instrument (e.g. Ammeters, Volt-

meters, energy meter etc.) installed in a Sub-Station to maintain which over the ckt quantities. The instrument transformer are invariably used with them for satisfactory operation.

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132KV

1.8.6 Miscellaneous equipmentIn addition to above, there may be following equipment in a Sub-Station.

i) Fuses.ii) Carrier-current equipment.iii) Sub-Station auxiliary supplies.

1.8.7.Protective relay“A protective relay is a device that detects the fault and initiates the

operation of the C.B. to isolate the defective element from the rest of the system”. The relay detects the abnormal condition in the electrical circuit by constantly measuring the electrical quantities, which are different under normal and fault condition. The electrical

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Ammeter

Temperature Gauge

quantities which may change under fault condition are voltage, current, frequency and phase angle. Having detect the fault, the relay operate to close the trip circuit of C.B.

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Distance Relay

1.8.8 Circuit breakerA circuit breaker is an equipment, which can open or close a circuit under

normal as well as fault condition. It is so designed that it can be operated manually (or by remote control) under normal conditions and automatically under fault condition. For the latter operation a relay wt. is used with a C.B. generally bulk oil C.B. are used for voltage up

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to 66 KV while for high voltage low oil & SF6 C.B. are used. For still higher voltage, air blast vacuum or SF6 cut breaker are used.

1.8.8.1 The type of the Circuit BreakerThe type of the Circuit Breaker is usually identified according to the medium of arc extinction. The classification of the Circuit Breakers based on the medium of arc extinction is as follows:(1) Air break' Circuit Breaker. (Miniature Circuit Breaker).(2) Oil Circuit Breaker (tank type of bulk oil)(3) Minimum oil Circuit Breaker.(4) Air blast Circuit Breaker.(5) Vacuum Circuit Breaker.(6) Sulphur hexafluoride Circuit Breaker. (Single pressure or      Double Pressure).Type Medium Voltage, Breaking Capacity1 – Air break Circuit Breaker

Air at atmospheric pressure

(430 – 600) V– (5-15)MVA(3.6-12) KV - 500 MVA

2 – Miniature CB. Air at atmospheric pressure

(430-600 ) V

3 – Tank Type oil CB. Dielectric oil (3.6 – 12) KV

4 – Minimum Oil CB. Dielectric oil (3.6 - 145 )KV5 – Air Blast CB. Compressed Air

(20 – 40 ) bar245 KV, 35000 MVAup to 1100 KV, 50000 MVA

6 – SF6 CB. SF6 Gas 12 KV, 1000 MVA

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36 KV , 2000 MVA145 KV, 7500 MVA 245 KV , 10000 MVA

7 – Vacuum CB. Vacuum 36 KV, 750 MVA 8 – H.V.DC CB. Vacuum , SF6 Gas 500 KV DC

1.8.8.2 Breaker Used in 132KV Grid Station

Oil Circuit Breaker Vacuum Circuit Breaker SF6 Circuit Breaker

Oil Circuit BreakerBulk Oil Circuit Breaker

Low Oil Circuit Breaker Consists of two parts Supporting Chamber Circuit-Breaking Chamber( Consists of fixed and moving contact)

Disadvantages Of Oil Circuit BreakerIt may form explosive mixture with air.Its requires frequent maintenance.Absorb moisture so reduces dialectical strength.

1.8.8.3 Vacuum Circuit BreakerVacuum is used as an arc quenching medium.Have more insulating strength.10-7 to 10-5 pressure is maintained.

Advantages

Compact, reliable and have longer life. No fire hazards. No generation of gas during and after operation. Can interrupt any fault current. No noise is produced while operating. Require less power for control operation.

1.8.8.3 SF6 Circuit Breaker Sulphur Hexafluoride used in arc quenching medium. SF6 is electro-mechanical gas. It has strong tendency to absorb electron. It is much more effective for high power and high voltages.

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Advantages Simple construction, less cost. SF6 gas is not catches flame, non toxic & chemically inert gas. Maintenance free. Ability to interrupt low and high fault current.

1.8.9 Power TransformerPower transformer is a static electrical device, involving no continuously moving parts,used in electric power systems to transfer power between circuits through the use of electromagneticinduction. The term power transformer is used to refer to those transformers used between the generator and the distribution circuits, and these are usually rated at 500 kVA and above. Power systems typically consist of a large number of generation locations, distribution points, and interconnections within the system or with nearby systems, such as a neighboring utility. The complexity of the system leads to a variety of transmission and distribution voltages. Power transformers must be used at each of these points where there is a transition between voltage levels. Power transformers are selected based on the application, with the emphasis toward custom design being more apparent the larger the unit. Power transformers are available for step-up operation, primarily used at the generator and referred to as generator step-up (GSU) transformers, and for step-down operation, mainly used to feed distribution circuits. Power transformers are available as single-phase or three-phase apparatus.

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SF6 GasPressure Gauge

Transformer is a vital link in a power system which has made possible the power generated at low voltages (6600 to 22000 volts) to be stepped up to extra high voltages for transmission over long distances and then transformed to low voltages for utilization at proper load centers.

This flux induces an electro-motive force in the secondary winding too. When load is connected across this winding, current flows in the secondary circuit. This produces a demagnetizing effect, to counter balance this the primary winding draws more current from the supply so that

IP.NP = IS.NS

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Transformer ratings

Incoming # 01 20/26 MVAIncoming # 02 20/26 MVA

Incoming #03 31.5/40 MVAMaximum LoadTR1 113/1305 ATR2 113/1305 ATR3 175/2008 A

1.8.9.1 PARALLEL OPERATION OF THREE-PHASE TRANSFORMERS

Ideal parallel operation between Transformers occurs when (1) there are no circulating currents on open circuit, and (2) the load division between the Transformers is proportional to their kVA ratings. These requirements necessitate that any - two or more three phase Transformers, which are desired to be operated in parallel, should possess:

1) The same no load ratio of transformation;

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2) The same percentage impedance;3) The same resistance to reactance ratio;4) The same polarity;5) The same phase rotation; 6) The same inherent phase-angle displacement between primary and secondary

terminals. The above conditions are characteristic of all three phase Transformers whether two winding or three winding. With three winding Transformers, however, the following additional requirement must also be satisfied before the Transformers can be designed suitable for parallel operation.

7) The same power ratio between the corresponding windings.

The first four conditions need no explanation being the same as in single phase Transformers.

The fifth condition of phase rotation is also a simple requirement. It assumes that the standard direction of phase rotation is anti-clockwise. In case of any difference in the phase rotation it can be set right by simply interchanging two leads either on primary or secondary. It is the intention here to discuss the last two i.e., sixth and seventh conditions in detail.

1.8.10 Bus-Bar Schemes used in a sub station

1.8.11 Bus-Bar Isolator

1 – Bus-Bar Isolator. (Disconnector Switch)2 – Maintenance Earth Switches. 3 – CT's For Transformer protection. 4 – Circuit Breaker. 5 – CT's for Bus-Bar protection and metering. 6 – Maintenance Earth Switches. 7 – Transformer Isolator.

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1.8.12 Bus-couplerBus coupler is a device which is used switch from one bus to the other without any interruption in power supply and without creating hazardous arcs. It is achieved with the help of circuit breaker and isolators. Bus coupler is used in sub-station for changing the source of supply without interrupting the transmission. Let we have two source feeders A1(132KV) & A2(132KV). And initially A1 is connected via transfer bus, main bus, bus coupler 1 to transformer. Now we want to change source feeder A1 with A2, the Bus coupler comes into play. 1st we connect all three phases of feeder A2 to Transfer bus which in turn connected to main bus in parallel to transfer bus of feeder A1.Since both are in parallel so there neither be any damage nor any interruption in supply takes place. Thus we have same value (132KV) supply from combined sources in our main bus. Now we connect the bus coupler of A2 and disconnect bus coupler of A1.next, we remove the transfer bus connection of A1 from main bus followed by disconnecting all three phases.Now our supply is completely through feeder A2 and bus coupler 2.

1.8.13 Battery A battery is a device that converts the chemical energy contained in its active materialsdirectly into electric energy by means of an electrochemical oxidation-reduction (redox)reaction. In the case of a rechargeable system, the battery is recharged by a reversal of theprocess.

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Bus-coupler

1.8.13.1 Batteries Room Batteries are very important part of the grid. It works as a standby storage device, that provides D.C power to the grid’s dc supply equipment in case of failure of A.C supply. Different protection devices i.e relays, circuit breakers and other control equipment of relay room, 11KV control room, 132KV control room and yard operates on 110 D.C volt supply that is normally supplied by a rectifier. In case of failure of A.C power batteries works as a standby source of 110 D.C supply. No. of cells installed = 55 2 Volt/cell, 150 AH Total Output Voltage = 110 Volt. Recommended Float Voltage = 202 Volt/cell at 25 CRecommended Boost Voltage = 2.4 Volt/cell Minimum 2.8 Volt/cell MaximumTotal Float Voltage = 121 Volt

1.8.14 Lighting arrestorA lightning arrester is a device used on electrical power systems to protect the insulation on the system from the damaging effect of lightning. Metal oxide varistors (MOVs) have been used for power system protection since the mid 1970s. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth.

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1.8.15 Capacitor Capacitors are used in substation to improve power factor.

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Lighting arrestor

Capacitor bank

1.9 Outgoings of 132 KV Substation Bosan Road Multan

Raza Hall Express Usmanabad Hazori bagh Wapda colony Gulgusht Eidgah Shamsabad Sabzazar Shalimar Gray vala Hussain agahi University P.K.Colony

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