1. INTRODUCTION

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1.1 INTRODUCTION

The 12MW bio-mass power plant switchyard functions are to receive energy

transmitted at high level voltage from our generating stations ,reduce the voltage to a value

appropriate for local distribution and provide facilities for switching, thus o8ur switchyard

132/11kv step-down & step-up transformer. both are using step-up &step-down power

generating transformer .so generation supplying the voltage 11kv and then switchyard

protecting and metering used to ct`s &pt`s. transformers are installed on substations to

transform the power from one voltage level to another level as per needs.

Fig 1.1:- Block Diagram Of Power Plant

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The above single line diagram shows the plant view. The switchyard is placed after the

alternator as shown in above. This switchyard is for the purpose of power transmission that is

generated in the power plant. It is mainly consists of power transformer, Circuit breakers,

Isolators, Lightning arresters, Capacitor Voltage Transformers & the Differential relays. The

mentioned all above are the protective devices.

1.2 INTRODUCTION TO PROTECTION

Protection is the electrical equipment from faulty section the main objection of

protection is to quickly isolate a fault from the ends the est. of the system can function

satisfactorily the power system costs a very large capital investment so it should be protected

from hazards.

Faults can occur on any power system components like generator, transformer, and

motors etc. faults are generally falling in to two categories short circuit faults. Open circuit

faults, short circuit faults are resulting in very abnormal high current if they followed to persist

even for short period of time, it can lead to extensive damage to equipment.

Fault should be instantly detected and isolated healthy circuit with in shortest possible

time, it is not possible to do this manually can it be made automatically with protection

equipment like CB`s and CT`s relays.

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2. SWITCHYARD

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Fig:2.1. Switchyard layout

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2.2 SWITCH YARD DESCRIPTION

Switch yard is a place where the entire primary protecting equipment of the power

system is arranged in a systematic manner from generator transformer to feeders by connecting

the transmission lines.

Switchyard protects the generating station from the faults .it suppresses the faults by

making them not to reach the generating unit thus a switchyard plays a vital role in the

protection.

The switch yard mainly works on the purpose of stepping the grid voltage down to a

certain value. The switchyard under study works on 132/11kv i.e., the input of the transformers

132kv and It steps down to 11kv.the substation receives the 132kv from 220kv substation. The

received voltage is stepped down to the required value by using a three phase auto

transformer .the auto transformer is economically efficient compared the ordinary there phase

transformer. To step down the 132kv voltage to 11kv, auto transformer having 15mva capacity

is employed.

The three feeder lines are provided protection separately.teh protection system contains

a lightning arrester, cvt , wave trap , line isolator and ct respectively.teh rating of the protection

elements in the high voltage side are less compared to those on high voltage side of the auto

transformer.

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3. SWITCHYARD

EQUIPMENT

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3.1 TRANSFORMER(132/11KV 15MVA):

Most of the power transformers of 132/11kv and above are of star-delta vector grouping with the neutral solidly earthed. There are a few transformers with delta-star (delta on High voltage side).

Fig 3.1:.132/11KV, 15MVA Transformer

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3.1.1 GENERATOR TRANSFORMER:

The generator takes power that is fed to it by the alternator. Here the voltage at a lower

level is transformed into a higher level as the higher level transmission is very economical. A

transformer is a static device by means of which of which electric power in one circuit is

transformed into electric power of the same frequency in another circuit. it can rise or lower the

voltage in a circuit, but with a corresponding increase in current basically transformer will

work on mutual induction principle between two circuits linked by a common magnetic

flux .it is a star-delta power transformer the transformer is connected to the bus by a thin

laminated sheet conductors there by constant losses present in the bus can be eliminated to a

maximum extent. Thus the generator transformer connects the electromechanical alternator to

the static bus bar. The transformer protection is carried out by the buchholz relay. Differential

relay, distance relay, and lightning arrester, thus the important part of the switchyard.

SPECIFICATIONS OF THE TRANSFORMERCOOLING SYSTEM OIL NATURAL AND AIR NATURALFULL-LOAD CURRENT HV-65.6A, LV-787.3ATOTAL MASS 50000KGCORE AND COIL MASS 25800KGTANK AND FITTINGMASS 10800KGMASS OF OIL 13400KGOIL CAPACITY 15000LITRESGTD TEMP RISE OIL-450C, WINDING-500CMAX TEMPERATURE 500C

Table 3.1: Specifications Of The Transformer

3.1.2 AUXILARY TRANSFORMER

This is the one used for the maintaining the power supply to the auxiliaries and

accessories present in the power plant when the entire generating unit of the station is ruined.

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The transformer takes power from the grid to it is connected and the power is supplied. It is star

delta connected.

FIG 3.2:AUXILARY TRANSFORMER

RATING OF THE TRANSFORMER 11/0.44kV,2MVATOTAL WEIGHY 8100kgOIL QUANTITY 1350lit

Table 3.2 Specifications of Auxiliary Transformer

3.2 LIGHTNING ARRESTER

Lightning arrester is also known as surge diverter or surge arrester. They are connected

between the line and ground at the substation and always parallel with the equipment to be

protected and perform their function by providing a low impedance path surge currents, the

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surge arresters protective level is less, than surge voltage withstanding capacity of the

insulation equipment being protected. The lightening arresters protective level is that the

voltage appearing across the terminals of the arrester at spark over or during the flow of current

through the arrester after spark gap over. The purpose of lightening arrester is to divert or

discharge the surge to the ground.

FIG 3.3: LIGHTNING ARRESTER

The action of surge diverter can be studied when the travelling surge reaches the

diverter, it sparks over at a certain prefixed voltage and provides relatively low impedance path

to the ground for the surge current. The current flowing to ground through the surge impedance

of the line limits the amplitude of the over voltages across the line and ground known as

residual voltage to such a value which will protect the insulation of the equipment being

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protected. It is however, essential that low impedance path to must not exist before the over

voltage appears and it must cease to exist immediately after the voltage returns back to its

normal value.

There are two types of designs”

1. Metal oxide arrester

2. Conventional gapped arresters.

Among these two types of designs we use metal oxide type arresters.

RATING:132-145kV

3.3 CURRENT TRANSFORMER

The current transformer is basically a step up transformer.teh primary winding of the

current transformer is wound in series with the point where the current is to be sensed small

portion of the current flows in the secondary depending upon the turn`s ratio of the transformer.

If the value of the current is above the predetermined value, the relay operates which in

turn gives up a trip signal to the circuit breaker by which the circuit breaker isolates the faulty

system from the healthy system. As the current transformer is connected to the circuit

throughout the service, the losses that occur in the transformer are cooled with the help of

transformer oil. The oil should be maintained at a predetermined value.

To reduce the burden on the current transformers banks of capacitors are connected in parallel so that the voltage burden is eliminated thus the efficient operation of the system can be obtained.

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FIG 3.4 : CURRENT TRANSFORMER

RATIGS OF THE C.T

C.T RATIO 75/1A

TYPE 3 CORE

CORE 1

USAGE METERING

CLASS 0.5

BURDEN 15VA

CORE 2

USAGE PROTECTION

CLASS 5P20

BURDEN 20VA

CORE 3

USAGE DISTANCE PROTECTION

CLASS PS

Table 3.3: Ratings of Current transformers

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Current transformers are the instrumentation transformers which are used for the

metering and protection purposes. The CT ratio is about 600/300:5 through the CT the high

magnitude current is stepped down to a corresponding lower current. This current is used for

the metering purpose. The stepped down current when is exceeds a particular value it indicates

that some fault is occurred. Thus the trip circuit operates and the breaker opens the circuit .thus

the current transformer also operates as a protecting device.

3.4 CAPACITOR VOLTAGE TRANSFORMER(CVT):

Voltage transformers are used for measurement and protection.accordingly,they are

either measuring type or protective type voltage transformer.VT`S are necessary for voltage

,directional distances protection.the primary of VT`1S is connected to power circuit between

phase and ground.the volt ampere rating of VT is smaller as compared with that potental

transformer.

There are two types of constructions:-

1.Electromagnetic potential transformer in which primary and secondary are wound on

magnetic core as in the case of normally used transformers.

2.capacitor potential transformer in which the primary voltage is applied to a series capacitor in

a group.The voltage of auxilaryVT the secondary of auxilary VT is taken for measurement of

coupling capacitor.

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FIG 3.5 : CAPACITOR VOLTAGE TRANSFORMER

RATINGS OF CVTTYPE 2 CORECORE 1USAGE METERINGCLASS 0.5BURDEN 25VACORE 2USAGE PROTECTIONCLASS 3P

BURDEN 25VA

Table 3.4: Ratings of Current Voltage Transformers

3.4.1 APPLICATIONS OF CVT

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CVT`S are used for line voltmeters,synchroscope,protective relays,traffic metr eetc.the

performance of CVT is inferior to that electromagnetic voltage transformer.its performance is

affected by the supply frequency,switching transients,magnitude of burden connected etc.the

CVT is more economical than an electromagnetic VT,when thesystem voltage normally

increases above 66kv.the carrier current equipment can be connected to the capacitor of the

CVT`S thereby ther is no need of separate coupling capacitors.

Voltage type vt is used for 66kv and above.at such voltage cost of electromagnetic type

vts tends to be too high.the capacitors connected in series act like ppotential dividers provided

the current taken by the burden is neligible compared with the current passing through the

series connected capacitor.however theburden current becomes relatively larger and ratio eror

and also phase error is introducedcompensaton is carried out by tuning.the reactor connected in

series with the burden is capacitors.this eliminates the error .the constructiuon of capacitor type

vt depends on the form of cv divider.generally hv capacitors are enclosed in porcelain housing.

A large metal steel box at the base encloses the tuning coil intermediate transformer.

3.5 ISOLATORS:

Isolators are used for making breaking the circuits.isolators operate under no load

condition only.it does not have any speccific current breaking capacity or current making

isolator is not used even for breaking load currrents.

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FIG 3.6:ISOLATOR

RATING : 12-420KV

3.5.1 TYPES OF ISOLATOR

A. VERTICAL BREAK TYPE

B. HORIZONTAL BEAK TYPE

C. VERTICAL PANTOGRAPH TYPE.

The vertical pantograph type design is preffered for rated voltages of 420kv and

above.the other types of designs are used from 12-420kv .these are out door air break

disconnecting switch of the gong operated horizontal break type with rating of 7kv and above.

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3.5.2 OPERATING DUTY PERFORMANCE

Surge arresters must be operated rapidly in response to lightning over

voltages,switching over voltages and other surges and discharge.the energies of the surge safety

go ground .the use of a high spark voltage is to improve the follow current interrupting

capability should be avoided because it rescues the degree of protection offered by surge

arester.

3.5.3 HORIZONTAL BREAK CENTER ROTATING DOUBLE BREAK ISOLATOR

This type of construction has three insulator stacks per pole.the two on each side are

fixed and one at the center is rotating type.the central insulator stack can swing about its

vertical axis about 900 and the contact shaft swings horizontally giving a double break.the

isolators are mounted on a galvonized rolled steel frame.the three poles are interlocked by

means of steel shaft.a common operating mechanism is provided for all the three poles.isolators

are used in addition to C.B.`s are provided on each side of every C.B.`s to provide isolation and

unable maintainence ,which opening a circuit then the isolators are opened for then after circuit

breaker is opened .when closing a circuit breaker is closed first then isolators are

colsed.isolators may be manually operated or by motor mechanism or by pneumatic mechanism

the isolator consists of a junction point which us a common point to two posts,asa soon as he

swing between the two conducting post occurs tehn the insulation is obtained.

Current is passed through the primary windings of the standard C.T.andC.T under

test.the ratio of the C.T. can be determined by comparing the currents in ammeter A1 and A2.

1. Isolator operates under off load conditions .it doesnot have any specified current breaking

capacity or current making capacity.isolator is not even for breaking load currents .CB can

make and break electric under normal current or short circuit conditions.

2. Isolators are used in addition to cbs and are used while alosing a circuit the isolator is colsed

first and the cb next.

3. Isolators are necessary on supply side of cbs in order to ensure isolation of the cb from live

parts for the purpose of maintainence .automatic switching of isolators is preffered.

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4. Isolators used in powr systems are generally 3-pole isolator.teh 3pole isolator have three

identical poles.each pole mounted on a fabricated support.the conducting parts of copper

rodFixed and moving contacts during the opening operation the conducting rods swing apart

and isolation is obtained.the simultaneous operation of 3 poles is obtained by mechanical

interlocking of three poles.the isolators are operated either by manual operation or by electrical

motor mechanism.the isolators are operated locally where they are located .teh isoaltors are

opened and closed by means of motor mechanism always.if the motor are not working when

they are operated manually or locally.

3.6 CIRCUIT BREAKERS:

Faults ar inevitable in powr systems and as sson as the fault occurs ,the healthy sysyem

is to be isolated from the faulty system.teh seperation of the healthy system from faulty

system is done by the circuit breaker.as soon as the relay senses the unhealthy solution it gives

a trip signal to the cbs in seperation of the healthy system from the faulty system a movable

contact should be moved or seperated from the fixed contact with the application of some

external pressure as the contacts seperates potential gradient plays an important role and the

ambient conditions too.

The different types of cbs that come in hand in the protections of powr system are

AIR BLAST CIRCUIT BREAKERS,MINIMUM OIL CIRCUIT BREAKERS,VACCUM

CIRCUIT BREAKERS,SF6 CIRCUIT BREAKER.

3.6.1 SF6 CIRCUIT BREAKER

The circuit breaker we use in this 132/11kv switchyard is sf6 circuit breaker .for high

voltages such as 132kv and above voltges,we use this circuit breaker.

The sf6 circuit breaker will operate mainly on the princple of PUFFER princple in extra

high voltge operation.

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FIG 3.7: SF6 CITCUIT BREAKER

3.6.2 PUFFER PRINCIPLE

As the puffer cylinder moves downwards for the opening stroke,the pressure ratio p1/p2

raises and depends upon the throat diameter of the nozzle and speed of puffer cylinder the

pressure ratio increases to about s times during opening condition.the compressed gas is

released.Through the convergent-divergent nozzle.the arc is quenched at a current zero,for

higher interrupting ability,the flow pattern is optmised.

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*Puffer type sf6 breaker with insulating nozzle.

*Puffer type sf6 breaker with conducting nozzle.

Sf6 has the highest dielectric capacity so it is used for arc quenching capacity , as it has a

capacity of 2.35 times that of air and 30% less than that of the dielectric oil used in CB`s.

3.6.3 PROPERTIES OF SF6 CIRCUIT BREAKER

Hifgh dielectric strength.

Thermal and chemical stability.

Non- onfllamability.

Pure sf6 gas is inetr and thermally stable.

Arc extinguishing ability it should have a low dissociation temeperature,a short

theramal time constant.

It remains in a gaseous state upto a temperature of 9 degree c and its density is about 5

times that of air and the pre heat convention is 1.6 times as much as that of air.

A part from being as inert gas it is non-flammable ,non-poisonous and orduorless.

When arcing takes place through the gas some y-products are produced due to

break down of the gas .these by products are hazard to the health of the maintainence of

the perssonel and theefore proper fare should be taken.

Sf6 gas is an electro negative gas.

At a pressure of 3 atmospheres the dielectric strength of sf6 is about 2 times that

of air and compares very well with that of oil.even when gas is exposed to electric are

for fairly long periods it has been found that decomposition effects are small and the

dielectric strength is not materially affected.on the other hand the metallic flourides that

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are formed at the higher temperatures are good insulators and are therefore not at all

harmful to the breaker.

3.6.4 DRIVING MECHANISMS

This type of cbs can be actuated by:

Manual operation.

Closing and opening by remote control.

Motor driven.

Pneumatic drive.

The method of pneumatic mechnism is being followed for the operation of the circuit breaker.

3.6.5 MERITS

Out door EHV sf6 has less number of interrupts per pole than abcb and minimum oil

circuit breaker.

The gas is non-inflammable and chemically stable.

Small gas is re circulated in the circuit.hence requirment of sf6gas is small.

No frequent contact replacement.no over voltage problems.

Due to the superior arc uenching property of sf6,such cb`s have very short arcing time.

Sincethe dielectric strength of sf6 gas is2-3 times that of air such breakers can interrupt

much larger currents.

The sf6 cb gives noise less operation due to its colsed gas circuit and in exhaust too

atmosphere unlike the air blast circuit breaker.

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The cosed gas enclosure keeps the interior dry so that there is no moisture problem.

There is no risk of fire in such breaker because sf6 gas is non-inflammable operation.

The sf6 breakers have low maintainence cost light foundation requirements and

minimum auxilary equipment.

No frequent contact replacement.

3.6.6 DE-MERITS

SF6 breakers are costly due to the high cost of sf6.

Since sf6 gas has to be reconditined after every operation of the breaker additional

equipment is required for this purpose.

Sealing problems arise.imperfect joints lead to lekage of gas.

Arced sf6 gas is poisonous and should not be inhaled.

Influx of moisture in the breaker is harmful to sf6 gas cbs .several failures are reported

due to this cause.

The internal parts should be cleared throughly during periodic maintainence under

clean,dry environment.dust of teflon and sulphides should be removed.

3.6.7 PROTECTIVE RELAYS:

Protective Relays are the devices that detect abnormal conditions in electrical circuits

by constantly measuring the electrical quantities, which are different normal and fault

conditions.

The Functional Requirements of the Relay:

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1. Reliability: the most important requisite of protective relay is reliability since they supervise

the circuit for a long time before a fault occurs, if a fault then occurs, the relays must respond

instantly and correctly.

2. Selectivity: the relay must be able to discriminate (select) between those conditions for

which prompt operation is required and those for which no operation or time delayed operation

are required.

3. Sensitivity: The relaying equipments must be sufficiently sensitive so that is operates reliably

when required under the actual condition that produces least operation tendency.

4. Speed: The relay must operates at the required speed it should neither be too slow which may

result in damage to equipment nor should it be too fast which may result in undesired

operation.

3.6.8 INTERNAL BUS TRANSFORMER:

All the generating units in a power station may not of same capacity in voltage, so the

power that is fed from the alternator to the buses via transformer may be of same voltage. So to

parallel all the generating units in the power plant the buses should be of same voltage. To

parallel the buses the inter bus transformer is used. By this different rated busses will be made

into a unit of same potential so entire plant can be synchronized with the grid.

3.6.9 BUS COUPLER:

Generally in switchyard a stand by bus is maintained to have continuity of power

supply. If the main bus is under problem of operation or to the handle the heavy loads with a

single bus cannot be carried out. The parallel connecting of the two buses is carried out with the

help of the bus coupler. It is similar to an isolator which connects the load circuit.

3.6.10 WAVE TRAPS:

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The transmission power frequencies contain the components of higher magnitude (in

KHz) along with the normal frequencies (40-60Hz). But all the electrical devices are designed

to operate at 50Hz frequency. Hence wave traps are used to attenuate the higher magnitude

frequencies ad allow only operating frequencies. The wave trap also adds back the higher

magnitude frequencies at the end of the line leaving the substation.

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4. SWITCHYARD

MAINTAINENCE

4.1 GROUNDING SYSTEMS:

4.1.1.GROUNDING PURPOSE

A safe grounding design has two objectives to carry electric currents into earth under

normal and fault conditions without exceeding operating and equipment limits or adversely

affecting continuity of service and to assure that a person in the vicinity of grounded facilities is

not exposed to the danger of electric shock.

The existence of a low station ground resistance is not, in itself, a guarantee of safety.

During fault conditions, the flow of current to earth will produce potential gradients that may

be of sufficient magnitude to endanger a person in the area. Also, dangerous potential

differences may develop between grounded equipment and structures and nearby earth.

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The measured soil resistivity obtained by field exploration is used to determined the

amount of ground grid necessary to develop the desired ground mat resistance. The resistance

to ground of all power plant, dam, and switchyard mats when connected in parallel should not

exceed, if practicable, 0.5 ohm for large installations. For small (1500 kW) plants, a resistance

of 1 ohm is generally acceptable. Practical electrode drive depth should be determined in the

field. A depth reaching permanent moisture is desirable. The effective resistance of, and the

step and touch potentials for, an entire ground mat with a number of electrodes in parallel can

be determined .The diameter of the electrode is determined by driving requirements. Copper-

weld ground rods of 3/4 in. diameter usually satisfactory where driving depths do not exceed 10

ft. For greater depths or difficult soil conditions,1-in.-diam rods are preferred. Galvanized pipe

is not suitable for permanent installations.

The depth and condition of the soil upstream from the dam on the flood plain is

frequently favorable for placement of one or two ground mats. These can be used for the

grounding of the equipment in the dam and leads extended to the grounding network in the

powerhouse. At least one ground mat should be provided under or near the switchyard.

4.1.2 SWITCHYARD GROUNDING:

a. COPPER CONDUCTORS.

A grid of copper conductors should be installed beneath the surface of the switchyard to

prevent dangerous potential gradients at the surface. The cables should be large enough and be

buried deep enough for protection from mechanical damage. The cables’ current-carrying

capacity under fault conditions and during lightning discharges should be checked. Under all

conditions, the grid serves to some extent as an electrode for dissipating fault current to ground.

b. GROUND RODS.

If warranted by soil conditions, a system of ground rods should be installed with the

grid to provide maximum conductance to ground.

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c. GROUNDING PLATFORM.

A grounding platform consisting of galvanized steel grating set flush in the gravel

surfacing or a grounding mesh buried 12-18 in. below grade should be provided at each

disconnecting switch handle. The platform or mesh should be grounded to the steel tower and

to the ground network in two places.

d. GROUNDED EQUIPMENT.

Grounded switchyard equipment includes tanks of circuit breakers; operating

mechanisms of disconnecting switches, hinged ends of disconnect grounding blades,

transformer tanks and neutrals, surge arresters, cases of instrument transformers and coupling

capacitors, and high-voltage potheads. Isolated conduit runs, power and lighting cabinet

enclosures, and frames of electrically operated auxiliary equipment should also be grounded.

Separate conductors are used for grounding surge arresters to the ground network. Fences,

including both sides of any gates, and other metal structures in the switchyard, should be

grounded to the switchyard grid at intervals of about 30 ft. If the fence gates open outward, a

ground conductor shall be provided approximately 3 ft outside the gate swing radius. Each

switchyard tower should be grounded through one leg. All structures supporting buses or

equipment should be grounded. If the network does not extend at least 3 ft outside the fence

line, separate buried conductors should be installed to prevent a dangerous potential difference

between the ground surface and the fence. These conductors should be connected to both the

fence posts and the ground network in several places.

e. OVERHEAD GROUND WIRES.

Overhead ground wires should be bonded securely to the steel structure on one end only

and insulated on the other to prevent circulating

Current paths.

4.1.3 GROUNDING DEVICES:

a. CABLES.

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Grounding cable used for direct burial or embedding in concrete should be soft-drawn

bare copper. Sizes larger than No. 6 AWG should be stranded.

b. ELECTRODES.

Electrodes for driving should be copper-weld rods of appropriate diameter and

length .Desired lengths can be obtained on factory orders.

c. EXTERIOR CONNECTIONS.

Ground cable connections to driven ground rods, any buried or embedded connections,

or any exposed ground grid connections should be made either with an appropriate molded

powdered metal weld or by a copper alloy brazed pressure connector.

d. INTERIOR CONNECTIONS.

Pressure clamp (bolted)type terminal lugs should be used for interior work. For neatness

of appearance of interior connections, embedded grounding cables may terminate on or pass

through grounding inserts installed with the face of the insert flush with the finished surface.

Connection to the apparatus is made by bolting an exposed strap between a tapped hole on the

insert and the equipment frame.

e. TEST STATIONS.

Test stations should be provided for measuring resistance of individual mats and

checking continuity of interconnecting leads. Where measurement sare contemplated, the

design of the grounding systems should avoid interconnection of ground mats through

grounded equipment, overhead lines, and reinforcing steel.

f. EMBEDDED CABLE INSTALLATION.

Embedded ground cables must be installed so movement of structures will not sever or

stretch the cables where they cross contraction joints. Suitable provision should be made where

embedded cables pass through concrete walls below grade or water level to prevent percolation

of water through the cable strands.

g. CONDUIT.

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Grounding conductors run in steel conduit for mechanical protection should be bonded

to the conduit. Control cable sheaths should be grounded at both ends. Signal cable shields are

grounded at one end only.

4.2 TRANSFORMER OIL INSULATION TESTING:

Transformer Oil is subjected to temperature test so by this we can know the properties

of the oil and any change occurs oil will be replaced.

The DP of paper can be determined in the laboratory utilizing ASTM method D-4243.

Acquisition of a paper sample is an invasive and expensive procedure that requires taking the

unit off line. A non invasive alternative has been developed recently. The procedure is based on

the determination of oil soluble cellulose decomposition products. These compounds,

substituted furans, are shown in Figure 2.Weidmann Diagnostic Solutions can isolate these

compounds from an oil sample and analyze them with High Performance Liquid

Chromatography, HPLC. Detection limits are at the 10 PPB concentration level. The most

significant compound is 2-Furfuraldehyde and concentrations of this compound have been

correlated with DP. Chendong has developed an empirical correlation between the

concentration of2-Furfuraldehyde and the DP.

Log [Fur] = 1.51 - 0.0035 DP

where [Fur] = conc. of 2-Furfuraldehyde in PPM. This equation, though not exact, allows one

to estimate the DP of cellulose insulation. Knowing the DP value, one can estimate the

remaining insulation life of a transformer.

4.3 RESISTANCE PITTS:

The earthing resistance indicates the easiness of providing a path. It should be as low as

possible. Different countries having standard values. In India, for commercial applications its

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<1ohm, and for railway its< 0.5 ohm. For air craft and ships temp. earthing <10 ohm.etc. Earth

resistance of earth pits shall depend on the terrain in which the same is provided. Accordingly,

based on soil resistivity data of the location, no. of earth pits is determined to ensure Grid earth

resistance value below 5 Ohms for electrical grids, for solidly grounded neutral of transformers,

resistance between Neutral & Body earth as well as panel earth shall be zero.

OTHER EQUIPMENT MAINTAINENCE

Other equipments are fed to test yearly once they will be checked and replaced if

necessary.

CONCLUSION

Protection means protecting the electrical equipment from faulty section to healthy

section. The main objective of the protection is to quickly isolate a fault from both the ends; the

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rest of the system can function satisfactorily. The power system costs a very large capital

investment, so it should be protected from severe hazards.

Faults can occur on any power system components like generator, transformers, motors

etc. Faults are generally falling in to two categories short circuit faults, Open circuit faults.

Short circuit faults are resulting in very abnormal high current if they followed to persist even

for short period of time, it can lead to extensive damage to equipment.

Faults should be instantly detected and isolated from healthy circuit with in shortest

possible time, it is not possible to do this manually can it be made automatically with protection

equipment like CB’s CT’s and relays. These protecting devices are placed in an area called

SWITCHYARD.

Switchyard is a place where the entire primary protecting equipment of the power

system is arranged in a systematic manner from generator transformer to feeders by connecting

the transmission lines.

Switchyard protects the generating station from the faults. It suppress the faults by

making them not to reach the generating unit thus, a switchyard plays a vital role in the

protection

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