Project report of transmission type eletrical substation

7/29/2019 Project report of transmission type eletrical substation

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Vocational Training

Report

Study of an transmittion type

electric sub-station

During

01- june 2013 to 30 june -

2013

At

csptcl 400/220/33 kv sub-

station, khedamara, bhilai (c.g.)

By shashikant sinha

6th sem, eee, ssitm, bhilai (c.g.)


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acknowledgement

Training work provides an intuitive for

students to utilize theoretical knowledge in

practical work .

I am thankful to Mr. M.K. Parmar, Executive

Engineer, for giving us permission to do training

in this sub-station.

I greatly acknowledge the hearty

cooperation of CSPTCL , KHEDAMARA ,

management, especially ..

Mr. Harish Kumar Dewangan ( Asstt. Engineer)

Mr. O.P. ( Asstt. Engineer)

Mr. Ashish Ratre ( Asstt. Engineer)

for their support and guidance whose work

has assisted in the preparation of our

report.

Above all we would like to acknowledge

our training in charge Mr. SUDHANSHU

TRIPATHI sir who checked our report work ,guided us and came to the rescue by

providing various hints about our report work

.

My friends have helped out along the way ,

by discussing ideas or reading chapters

I heartly offer my profound gratitude toall..


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Introduction

Before describing about the substation, we should have some knowledge that what a

substation do? Or simply what is substation?

Substation serves as a source of energy supply for the local areas of distribution in

which these are located. A substation is convenient place for installing synchronous

condensers at the end of the transmission lines for the purpose of improving power

factor and make measurement to check the operation of the various parts of the

power system.

Here, we discuss the 400/220/33 KV substation situated at Khedamara, Bhilai

(C.G.). This is basically a step down transmission substation which delivers bulk

power from power stations to load centers & large industrial consumers. Here,

regional load dispatch centre have been established for coordinating the activities of

state load dispatch centers. Here, we came to know that the voltage can be of 33,

220, 400 KV depending upon the length of transmission line and the amount of

electrical power to be transmitted.

The above referred substation is under Chhattisgarh State Power Transmission

Company Limited (CSPTCL) which is an undertaking unit of government of

Chhattisgarh.


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Single Line Diagram Of 400/220/33 KV substation

Khedamara, Bhilai (C.G.)


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Total Number Of Lines Incoming & Outgoing At The

Substation

Khedamara substation, Bhilai (C.G.), is a step down transmitting 400/220/33KV

substation type. Supply coming at 400 KV which is step down to 220 KV level and33 KV ( for internal substation supply ). In substation, two main buses are provided

for 400 KV side and two main buses and a single transfer bus is provided for 220

KV side. 400 KV and 220 KV lines are as follows :-

400 KV Lines :-

1) 400 KV PGCIL Raipur I

2) 400 KV Chandrapur

3) 400 KV Koradi

4) 400 KV Seoni

5) 400 KV Korba West ( Bilaspur ) Extension I

6) 400 KV BHATAPARA

7) 400 KV NTPC Korba I

8) 400 KV NTPC Korba II

9) 400 KV Raita

220 KV Lines:-

1) 220 KV BSP I

2) 220 KV BSP - II

3) 220 KV BRSS - I

4) 220 KV BRSS II

5) 220 KV PGCIL

6) 220 KV Urla

7) 220 KV Bemetara I

8) 220 KV Thelkadih - I


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Equipments Installed In Sub-Station

1) Power transformer

2) Current transformer

3) Potential Transformer

4) Capacitive Voltage Transformer

5) Lightening Arrestor

6) Circuit Breaker

7) Relay

8) Reactor

9) Bus-Bar

10) Wave Trap

11) Isolator

12) Insulator


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13) Battery & Battery Charger

14) Control Panel

15) Control Cables & Conductors

16) Power Line Carrier Communication

Power Transformer

A Transformer is a static electrical device that transfers energy by inductive

coupling between its winding circuits. An alternating current in the primary winding

creates a varying magnetic flux in the transformer's core and thus resulting in a

varying magnetic flux through the secondary winding. This varying magnetic

flux induces an alternating electromotive force (emf) orvoltage in the secondary

winding as output.

Power transformers are used for stepping up the voltage for transmission at

generating stations and for stepping down the voltage for further distribution at main

step down transformer substation. Usually naturally cooled, oil immersed cooling

techniques are used for 10MVA capacity transformers. The transformers of rating
http://en.wikipedia.org/wiki/Inductive_couplinghttp://en.wikipedia.org/wiki/Inductive_couplinghttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Electromagnetic_inductionhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Inductive_couplinghttp://en.wikipedia.org/wiki/Inductive_couplinghttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Electromagnetic_inductionhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Voltage


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higher than 10MVA usually used blast air cooling method. For very high rating

transformers forced air cooling, watercooling and air blast cooling may be used.

At 400/220/33KV substation, Khedamara, Bhilai, total seven power

transformers were installed of which six 105MVA 1- auto transformers and one

315MVA 3- transformer in which OFAF cooling system had been installed.

Name Plate Details of 105MVA 1- Transformer

COMPANY BHELTYPE OF COOLING ONAN/ONAF/OFAFMVA RATING HV 42.0 / 63.0 /105MVA RATING IV 42.0 / 63.0 / 105MVA RATING LV 12.6 / 18.9 / 31.5

TEMPERATURE RISE OIL 50

TEMPERATURE RISE WINDING 55

NO LOAD VOLTAGE HV 400/

NO LOAD VOLTAGE IV220/ KV

Circuit Diagram of 105 MVA


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NO LOAD VOLTAGE LV 33KVLINE CURRENT HV (AMP) 181.9 / 272.8 / 454.7 ALINE CURRENT IV (AMP) 330.6 / 496.0 / 826.6 ALINE CURRENT LV (AMP) 381.8 / 572.7 / 954.5 A

INSULATION HV 1300KVpINSULATION IV 950KVpINSULATION LV 250KVp

FREQUENCY 50Hz

Name Plate Details of 315MVA 3- Transformer

COMPANY BHELTYPE OF COOLING ONAN/ONAF/OFAFMVA RATING HV 189.0 /252.0 / 315.0

MVA RATING LV 63.0 / 83.0 / 105.0TEMPERATURE RISE OIL 40

TEMPERATURE RISE WINDING 45

NO LOAD VOLTAGE HV 400

NO LOAD VOLTAGE IV 220 KVNO LOAD VOLTAGE LV 33 KV

LINE CURRENT HV (AMP) 454.8 A

LINE CURRENT IV (AMP) 826.6 ALINE CURRENT LV (AMP) 1837 A

INSULATION HV HVIS1050KVpLi1300KVpAC 38KVpINSULATION IV Li 950KVp AC 38KVpINSULATION LV Li 250KVp AC 38KVp

FREQUENCY 50Hz

Testing Of Power Transformer

Insulation Resistance Test

Insulation Resistance test is an essential type test. This test is carried out to

ensure the healthiness of overall insulation system of an electrical power

transformer.

o Procedure of Insulation Resistance test of transformer

First disconnect all the line and neutral terminals of the transformer. Megger leads to be connected to LV and HV bushing studs to measure

Insulation Resistance IR value in between the LV and HV windings.


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Megger leads to be connected to HV bushing studs and transformer tank earth

point to measure Insulation Resistance IR value in between the HV windings

and earth.

Megger leads to be connected to LV bushing studs and transformer tank earth

point to measure Insulation Resistance IR value in between the LV windings

and earth.

NB : It is unnecessary to perform insulation resistance test of transformer perphase wise in three phase transformer. IR values are taken between the windings

collectively as because all the windings on HV side are internally connected

together to form either star or delta and also all the windings on LV side are

internally connected together to form either star or delta.

Measurements are to be taken as follows:

For Auto Transformer: HV-IV to LV, HV-IV to E, LV to E For Two Winding Transformer: HV to LV, HV to E, LV to E

Three Winding Transformer: HV to IV, HV to LV, IV to LV, HV to E, IV to E, LV to E

Oil temperature should be noted at the time of insulation resistance test oftransformer. Since the IR value of transformer insulating oil may vary withtemperature.

IR values to be recorded at intervals of 15 seconds, 1 minute and 10 minutes. With

the duration of application of voltage, IR value increases. The increase in IR is anindication of dryness of insulation.

Polarization Index Test

It is a ratio of the insulation resistance taken of transformer for 60 sec to the

insulation resistance taken of transformer for 15 sec.

Ratio Test

Absor tion Coefficient =

Polarization Index=

Kab Absor tion Coefficient =


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This test can be done using a calibrated voltmeter, but it is preferable to do with a

special apparatus call ratio-meter.

This consists of a small portable transformer with a fixed primary, and a secondary

winding having a large no. of taps connected to two selector switches, one course

and the other fine so that any voltage desired could be obtained for direct reading.

The HV side of the transformer under test is connected to a LV main supply say 400

or 220 volt and the induced voltage on the secondary winding is compared with the

voltage output of the ratio meter, after insuring that the two voltages are in

opposition. Accurate readings are obtained by an ammeter connected between the

two winding so that the circulating current, due to the difference in the potential may

be detected. Ratio test should be conducted on every transformer, as any ratio error

detected in the winding may then be readily rectified. The permissible tolerance is 0.5 % of the declared ratio.

FIG:- Ratio test by using Selector Switch

L.V. WINDING OF Xmer

UNDER TEST

SUPPLY

H.V. WINDING OF

Xmer

UNDER TEST

FINE

GRADUATIONS

RATIO METER

TRANSFORMER

COARSE

GRADUATION A

V


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Short Circuit Test

In this short circuit test, the secondary winding is short circuited and rated secondary

current is circulated, the power input represents total I2R loss in primary plus

secondary winding and also stray losses. In this test the terminals of LV side are

short circuited by means of copper jumpers.

Three phase symmetrical adjustable low voltage is applied to HV winding. The

applied voltage is gradually increased till rated current are circulated via secondary

winding (supplied voltage = 5-10% of rated voltage because higher voltage will burn

the winding).

The measurement of primary voltage, primary current and power input, secondary

current are made during short circuit test. When rated current on secondary side the

input power represents total load loss. This is measured and is adjusted to standard

reference temperature say 75 .The total loss includes copper loss (I2R loss), a small

core loss(5 % of copper loss).

The total measured in this test is useful in determining the efficiency of power

transformer. This short circuit test reveals the various defects in the conducting

circuit ex- wrong transposition of conductors in the windings, breaks and fractures in

the parallel conductors, the use of conductors of wrong section, bad contacts etc.

z

Transform

erUnderTest

A2

A W

V

A1

Short

Circuit

HV LV

Variable

Voltage

Supply

Fig:- Short

circuit test of

1 Xmer

Fig:- Short circuit test

of 3- Xmer

3-

Transform

erUnder

Test

A

W

HV LV

Variable 3-

Reduced

Supply

Voltage W

V

V

HV

LV


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Current Transformer

A current transformer (CT) is used for measurement of alternating electric

currents in power supply line.

Current transformers, together with voltage transformers (VT) are knownas instrument transformers.

When current in a circuit is too high to directly apply to measuring

instruments, a current transformer produces a reduced current accurately

proportional to the current in the circuit, which can be conveniently connected to

measuring and recording instruments. A current transformer also isolates the

measuring instruments from what may be very high voltage in the monitored circuit.

Current transformers are commonly used in metering andprotective relays in

the electrical power industry.

Like any othertransformer, a current transformer has a primary winding, a magnetic

core, and a secondary winding. The alternating current flowing in the primary

produces an alternating magnetic field in the core, which then induces an alternating

current in the secondary winding circuit.

An essential objective of current transformer design is to ensure that the

primary and secondary circuits are efficiently coupled, so that the secondary current

bears an accurate relationship to the primary current. .A current transformer is

intended to operate normally with the rated current of the network flowing via the

primary winding which is inserted in series with network.

Name Plate Details of Current Transformer

COMPANY TELK HIGHEST SYSTEM VOLTAGE 420 KVRATED PRIMARY CURRENT 2000 A

RATIO 500-1000-2000/1 ASHORT TIME CURRENT 40 KA = Sec 1.0

FREQUENCY 50 HzINSULATION LEVEL KV 630/1425

SWITCHING IMPULSE VOLTAGE 1050 KVCORE NO. 1,2,4,5 PROTECTION

CORE NO. 3 METERING

Circuit Diagram of 420KV Current Transformer
http://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Electrical_power_industryhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Protective_relayhttp://en.wikipedia.org/wiki/Electrical_power_industryhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Alternating_current


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Burden on CT

The standard burden for voltage transformer is usually expressed in volt-amperes at

a specified power factor. The secondary load of a current transformer is usually

called the "burden" which is used to distinguish it from the load of the circuit whose

current is being measured. The burden, in a CT metering circuit is the

(largely resistive) impedance presented to its secondary winding. Burden refers to

the maximum load expressed in volt-amperes which may be applied across the

secondary terminal of CT in order to smoothly drive the load applied at secondary

terminal on current transformer.

Zb =
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Testing of Current Transformer (CT)

Polarity test

Each current transformer should be individually tested to verify that the polarity

marking on the primary and secondary windings are correct .The following figure

shows the test unit for this.

The ammeter A is a robust, moving coil,

permanent magnet centre zero type instrument. A

low voltage battery is used to energies the

primary windings through a single pole pushbutton. On closing the push button, with above

CT ammeter marking, the ammeter should give a

positive flick, indicating correct polarity of the

CT.

Primary Injection Test

This tets is carried out to ensure the CT ratio of current transformers. If this tets iscarried out after CT secondary wiring is completed it ensures not only the correct

ratio of CTs but also the correctness of the entire CT secondary wiring comprising

protection and metering portions.

The testing equipment consists of a loading (injection) transformer ,

controlled by a variable transformer to get the required current on the primary side of

the CT under test.

For carrying out the ratio test on CTs the following circuit is made use of.


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Secondary / Loop Resistance Test

Secondary resistance test is to verify the CT secondary winding resistance with

specified one and no discontinuity in the winding. This value can be used in other

calculations.

Burden test

Burden test is to ensure the connected burden to CT is within the rated burden,

identified on the nameplate.

Injected the rated secondary current of the CT, from CT terminals towards

load side by isolating the CT secondary with all connected load and observe the

voltage drop across the injection points. The burden VA can be calculated as

Magnetizing Curve Test

Magnetization Curve test is to confirm the magnetization characteristics of CT with

nameplate specification.

This test shall be conducted before ratio test and after secondary resistance and

polarity test, since residual magnetism left in the core due to DC test (polarity,

resistance), which leads additional error in ratio test.

The meters used for this test shall be having true RMS measurement.

The circuit connection shall be made as shown Figure. The primary should be openduring test.

Ohmmeter

Note-2

Ohmmeter

Note-1

Burden

P2

P1

S2

S1

Loop resistance to ensure load is connected properly

and circuits not left open. The circuit connection shall be

made for secondary resistance. Measure the dc resistance value

and record. The same shall be done for all taps and cores. These

values are influenced by temperature, so ambient temperature

must be recorded during this test. The circuit connection shall

be made as shown Figurefor loop resistance. Measure the dc

resistance including CT and load, phase by phase and values

can be compared between them.

Burden VA = Voltage drop * rated CT sec. Current.


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Demagnetization test

Before start the test demagnetize the core by Inject voltage on secondary terminals

and increase up to where considerable increment in current with small voltage

increment. Now start decreasing the voltage to zero, the rate at which increased.

Magnetization test

Now increase the voltage and monitor the excitation current up to the CT reaching

near to saturation point. Record the reading of voltage and current at several points.Plot the curve and evaluate the Vk and Img from the graph.

Turns Ratio Test

This test is to ensure the turns ratio of CT at all taps. The circuit connection shall be

made. The primary current of minimum of on primary side of CT with secondaries

shorted an measured and recorded for all cores.


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Potential Transformer

Potential Transformer orVoltage Transformer are used in electrical

power system for stepping down the system voltage to a safe value which can be fed

to low ratings meters and relays. Commercially available relays and meters used for

protection and metering, are designed for low voltage.There are three primary types

of voltage transformers (VT): electromagnetic, capacitor, and optical. Theelectromagnetic voltage transformer is a wire-wound transformer. The capacitor

voltage transformer uses a capacitance potential divider and is used at higher

voltages due to a lower cost than an electromagnetic VT. An optical voltage

transformer exploits the electrical properties of optical materials.

Primary winding of potential transformer are connected in parallel with the

main bus bar of the switchgear installation and to the secondary winding, various

indicating and metering instruments and relays are connected. When the rated high

voltage is applied to the primary of a PT the voltage of 110v appears across the

secondary winding. The ratio of the rated primary voltage to the rated secondary

voltage is known as turn or transformation ratio.

Fig-Circuit Diagram
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Name Plate Details of Potential Transformer

Normal system voltage 33 KVHighest system voltage 36 KV

Frequency 50 HzImpulse withstand voltage 170 KVp

Transformation ratio 150/5 A, 100/5 A, 50/5 A, 25/5 A

Rated output (VA burden) 15 VA

Burden of Potential Transformer

The standard burden for voltage transformer in secondary terminal is usually

expressed in volt-amperes at a specified power factor. The secondary load of a

potential transformer is usually called the "burden" which is used to distinguish it

from the load of the circuit whose voltage is being measured. The burden, in a PT

metering circuit is the (largely resistive) impedance presented to its secondary

winding. Burden refers to the maximum load expressed in volt-amperes which may

be applied across the secondary terminal of PT in order to smoothly drive the load

applied at secondary terminal on PT.

Testing of Voltage Transformer (PT)

IR values

For taking to earth value primary earth of terminal N is to be open while

in service it should be earth. The primary to earth IR value should be

taken by 5 KV range while secondary to earth value should be taken with

500V range.

Polarity Test

Zb =
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Polarity of potential transformer can be checked with the help of dry cell.

I n case of 220KV class PT deflection will be less hence we can check it

by giving voltage in secondary and connecting multi meter in secondary.

Ratio Test

Ratio of PT can be checked by application of single phase ac supply to

primary and measuring voltages in secondary.

Capacitor Voltage Transformer

A capacitor voltage transformer (CVT), orcapacitance coupled voltage

transformer (CCVT) is a transformerused inpower systems to step down extra

high voltage signals and provide a low voltage signal, for measurement or to operate

aprotective relay.

In its most basic form the device consists of three parts:

Two capacitors across which the transmission line signal is split, an inductive

element to tune the device to the line frequency,

A transformerto isolate and further step down the voltage for the

instrumentation or protective relay. The tuning of the divider to the line

frequency makes the overall division ratio less sensitive to changes in the

burden of the connected metering or protection devices.

The CVT provides following two purposes :

1. It is used for metering and protection purpose i.e. it steps down the service high

voltage into low voltage which feeds the potential coil of metering instruments

with proper calibration and also informs the protective relays.

2. It also provides a path for high frequency power line carrier communication

current or signals so that speech and data can be transmitted and received.
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Name Plate Details of Capacitor Voltage Transformer

PRIMARY SYSTEM VOLTAGE400000/ V

SECONDARY OUTPUT VOLTAGE110/ V 110/ V 110/ V

SECONDARY TERMINAL 1a-1n 2a-2n 3a-3n1a-1n 2a-2n 3a-3n

RATED BURDEN (VA) 100 100 100

CLASS 3P 3P 0.2*Protection Metering

FREQUENCY 48-51 Hz 49.5-50.5Hz

TOTAL SIMULTANEOUS BURDEN 100VA

INSULATION LEVEL 630/1425 KVp

HIGHEST SYSTEM VOLTAGE 420KV

CIRCUIT CAPACITANCE VALUE Cn=8800pf ; C1=9313pf ; C2=160000pf

Note:- link-3 to be removed only when carrier protection is used.

Danger:- Earth Link-1 of primary terminal box & earth link-3 of secondaryterminal box must not be removed while 400KV terminal is alive.


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Lightening Arrestor

A lightning arrester is a device used on electrical powersystemsand telecommunications systems to protect the insulation and conductors of the

system from the damaging effects oflightning. The typical

lightning arrester has a high-voltage terminal and a ground

terminal. When a lightning surge travels along the power line to

the arrester, the current from the surge is diverted through the

arrestor and gets to the earth. It is connected between the line

and the earth but before the connected equipments in the

substation. At 440/220/33 KV substation , Zinc-oxide (ZnO)type lightning arrester has been installed.

Properties of Zinc-oxide :

1. ZnO has relatively large direct band gap of 3.3eV at room

temperature.

2. Due to large band gap it induces higher breakdown voltage.

3. It has the ability to sustain large electric fields.
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4. It has low electronic noise and high temperature and high power operation.

5. It exhibits piezo-electric characteristics in thin film form.

6. They are light sensitive and luminescent.

ZnO lightning arrester is mainly constitutes of zinc-oxide variastor. Each variastor

has its own switching voltage. When lightning strikes the LA, the variastor get

punctured and thus allow thundering and lightning to circulate current via variastor

inflow the earth.

ZnO VARIASTOR Variastor is a voltage dependent resistor. Below their

breakdown voltage they offer infinite resistance. Once their breakdown voltage

exceeds they allow the circulating current to pass through it by offering negligible

resistance path.

Name Plate Details of Zinc-Oxide Lightning Arrestor

SYSTEM VOLTAGE 420 KV

RATED VOLTAGE 390 KV

CURRENT 10 KApMCOV 303 KV

PR. RELIEF CURRENT 40 KA

Circuit Breaker

A circuit breaker is made to operate mainly on

two occasions:-

One is during the maintenance operation and the

other is during any abnormal condition in the

power system.

A circuit breaker is a mechanical device

designed to close or open contact members, thus

closing or opening an electrical circuit under

normal or abnormal conditions.

In the 400/220/33 KV substation,

KHEDAMARA, the circuit breaker used are:-

400 KV side SF6(sulphur hexafluoride) circuit breaker


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220 KV side SF6 (sulphur hexafluoride) & Minimum oil circuit breaker

(MOCB).

33 KV side SF6(sulphur hexafluoride) circuit breaker & vacuum circuit

Breaker (VCB).

Minimum oil Circuit Breakers (MOCB):

Minimum Oil Circuit Breakers Mainly Consists of:

Breaker Pole

Base frame

Operating mechanism

Support structures

These designs place the interrupting units in insulating chambers at live Potential.

Unit Ratings: Up to 245 KV : two interrupters per pole

Operating Mechanism:

The operating mechanism mainly consists of a set of closing springs to close the

breaker with the required speed, a spring charging motor for charging of the closing

springs, limit switch mainly to break and make the power supply to the motor

depending upon the position of the closing springs trip/close, coils to trip/close the

breaker, control panel, auxiliary switch, levers, set of catches blocking devices etc.

for the effective and accurate functioning.

Working Principle or arc quenching in minimum oil circuitbreaker:

Working Principle of minimum oil circuit breaker orarc quenching in minimum

oil circuit breaker is described below. In a minimum oil circuit breaker, the arc

drawn across the current carrying contacts is contained inside the arcing chamber.

Hence the hydrogen bubble formed by the vaporized oil is trapped inside the

chamber. As the contacts continue to move, after its certain travel an exit vent

becomes available for exhausting the trapped hydrogen gas. There are two different

types of arcing chamber is available in terms of venting are provided in the arcing

chambers. One is axial venting and other is radial venting. In axial venting, gases


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(mostly Hydrogen), produced due to vaporization of oil and decomposition of oil

during arc, will sweep the arc in axial or longitudinal direction

SF6 Gas Circuit

Breakers :-

A circuit breaker in which

the contacts open and close in

SF6 media. Sulphur

hexafluoride (SF6) gas is an

alternative to air as an

interrupting medium. SF6 is a

colour less nontoxic gas, with

good thermal conductivity and

density approximately five

times that of air. SF6 is

chemically inert up to

temperature of 1500C and will

not react with metals, plastics,

and other materials commonly

used in the construction of

high voltage circuit breakers.

Available up to 800KV and

above. Most suitable for metal

clad and hybrid HV

substations.

Single Interrupter: 245 KV


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SF6 Circuit Breaker Name-Plate Details


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Company AREVAType GL316 with CR

Rated Voltage 420 KVFrequency 50 HZ

Power frequency withstand voltage

Open contacts 610 KVrmsTo earth 520 KVrms

Lighting impulse withstand voltage 1425KVpSwitching surge withstand voltage 1050KVp

Rated Short circuit Breaking CurrentSymmetrical 50 KA

Asymmetrical 61.2KARated Making Capacity 100 KA

Rated duration of short Circuit current time 3 S

Total Break Time 50 mSTotal Make time 160 Ms

Rated out of phase current 10 KALine charging breaking current 600A

First pole to clear factor 1.3Rated supply voltage

DC 220 VOperation Sequence O 0.3s CO

3min CO

AC 415 VRated SF6 Gas pressure at 20o C 6 Kgf/cm2

Rated air pressure 15 Kgf/cm2

Normal current 3150 AImpulse Level 1425 KVp

Year of Manufacture 2008

Relay

The relay is a protective device interposed between the main circuit and the

circuit breaker in such a manner that any abnormality in the circuit acts on the

relay, which in turn, if abnormality is of a dangerous character, causes breaker toopen and so to isolate the faulty element . The protective relay insures the safety


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of the circuit equipment from any damage which might otherwise caused by the

fault. Relays have three essential elements as illustrated below.

Sensing element

It is also called measuring element, it responds to the change in the actuatingquantity, The current in a protected system in case of over current relay.

Comparing element

It serves to compare the action of the actuating quantity on the relay with a

preselected relay setting.

Control Element

On a pickup of the relay, it accomplishes a sudden change in the control quantity

such as closing of the operative current circuit

Reactor

Trip Coil

Fault

A

Circuit to

be

protected

Trip

Circuit

Relay

contact

Relay Coil

Battery

Busbar


30/44

A Reactor is a coil having large inductive reactance in comparison to its ohmic

resistance. Reactors for

power systems in general

use and for industrial use

in particular exist as two

distinct functional types

series reactors for

fault-current limitation

and shunt reactors, either

for reactive

compensation and as two

construction types: air-

core air-insulated types

and liquid-insulated iron-

core types.

Reactors are used in combination with shunt capacitors to form harmonic filters or to

detune reactive compensation capacitor banks.

A shunt reactor is a reactor that is connected between the phase conductor and

neutral (or ground). A series reactor is connected in series with the phase conductor.

In this 400/220/33 KV sub-station, KHEDAMARA, only shunt reactors are installed.

Shunt Reactor

For Extra high voltage (EHV)

transmission lines, due to long

distance, the space between the

overhead line and the groundnaturally forms a capacitor parallel

to the transmission line , which

causes an increase of voltage along

the distance.

A shunt reactor is a reactor that is

connected between the phase

conductor and neutral (or ground).

Shunt reactors are installed to

offset the capacitive effect of transmission lines and thereby stabilizing the system

voltage within acceptable limits.


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Name Plate Details Of Shunt Reactor

50000 KVAR 50 Hz TYPE Air Core SSLR

3 Phase

S-S653/IEC-

289

Type of

cooling ONAN

Rated Voltage 420000 V

Rated Current 68.7 A Continuous Rating

Basic Insulation Oil Capacity

Line Neutral Power Frequency 630 KV

Lightning Impulse 1425KV 550 KV Radiator unit 4000 L

Switching Impulse 1080

KV

----

DATE MARCH 1982Power Frequency 630KV

230 KV

Impedance Weights

Positive Sequence 3460

Shield & Winding 58200 Kg

Tank & Fittings 23300 Kg

Zero Sequence 3460

Radiator Unit 10900 Kg

Oil 26100 Kg

Total 118500 Kg

Maximum Temperature Rise Up Tanking WeightOIL 4.5

at 441 KV

UPPER TANK 8500 Kg

WINDING 5.0 MIDDLE

TANK

5000 Kg

Up Tank Height

Upper tank 7900 mmMiddle tank 6600 mm

Bus-Bars


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Bus bar term is used for a main bar or conductor carrying an electric current to

which many connections can be made.

Bus bars are merely convenient means of connecting switches and other

equipment into various arrangements. The usual arrangement of connections in most

of the substation permits working on almost any piece of equipment withoutinterruption to incoming or outgoing feeders.

In some arrangements two buses are provided to which the incoming or

outgoing feeders and the principal equipment may be connected.

One bus is usually called the main bus and the other auxiliary or transfer bus .

Bus bar arrangement in CSPTCL 400/220/33 KV substation, KHEDAMARA:

220 KV BUS BAR ARRANGEMENT:-

Here the 220 kv bus arrangement Scheme is DOUBLE MAIN AND TRANSFER

BUS.

This is combination of MAIN AND TRNASFER BUS BAR SCHEME

and DUPLICATE BUS BAR SCHEME.

In this scheme loads are distributed on the two buses each with its own

transformer feed for normal operation, so that one bus fault will not cause a

complete outage of the station.

400 KV side-

2 Main buses :-

Main Bus 1

Main Bus 2

220 KVside-

2 Main bus & 1 Transfer bus

Main Bus 1

Main Bus 2

TRANSF

ER BUS

BUS-1

BUS-2

CBISOLATO

R

BUS COUPLER

CB


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Wave Trap

A wave trap is a parallel resonant circuit (inductor-capacitor tank circuit )

installed on the power line at local

substation. It is tuned to resonate at a

specific frequency or frequencies. These

frequencies are equivalent to the

transmission frequencies of the local

power line carrier transreciever.

This is relevant in power line carrier

communication.

Properly tuned, the wave trap shows its

highest magnitude of impedance (Z) at these carrier frequencies (105 KHZ and

above) , while permitting the 50 Hz power frequency to pass.

Wave trap is also known as line trap. A wave

trap traps the high frequency communication

signals sent on the line from the remote

substation and diverting them to thetelecom/teleportation panel in the substation

control room (through coupling capacitor &

LMU).

If wave traps are absent, the signal loss is more

& communication will be ineffective.

TUNING CIRCUITTYPE BBT Main Coil Inductance 1.0 mHNr. T 1676 Frequency Band 70/220 KHzWeight 9 Kg Protective Level(BIL) 140 KV


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Isolator

Circuit breaker always trip the circuit but open contacts of breaker cannot

be visible physically from outside of the breaker and that is why it is recommended

not to touch any electrical circuit just by switching off the circuit breaker. So for

better safety there must be some arrangement so that one can see open condition of

the section of the circuit before touching it. Such an apparatus is the isolating switch

(or isolator).

Isolator is a mechanical switch which isolates a part of circuit from system

as when required. Electrical isolators separate a part of the system from rest for safe

maintenance works.

So definition of isolator can be rewritten as, Isolator is a manually operated

mechanical switch which separates a part of the electrical power system normally at

off load condition.

Types of Electrical Isolators:

There are different types of isolators available depending upon system requirement

viz

As no arc quenching technique is provided in isolator it must be operated when there

is no chance of current flowing through the circuit. No live circuit should be closed

or open by isolator operation.

For voltages up to 145KV system, hand operated isolators are used whereas for

higher voltage systems like 245 KV or 420 KV and above motorized isolators are

used.

Constructional features of Double Break Isolators:-

These have three stacks of post insulators .The central post insulator carries a tubular

or flat male contact which can be rotated horizontally with rotation of central post

insulator. This rod type contact is also called moving contact.

The female type contacts are fixed on the top of the other post insulators which

fitted at both sides of the central post insulator. The female contacts are generally inthe form of spring loaded figure contacts. The rotational movement of male contact

causes to come itself into female contacts and isolators becomes closed. The rotation

Double Break Isolator, Centre Break Isolator, Pantograph type Isolator


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of male contact in opposite direction make to it out from female contacts and

isolators becomes open.

Rotation of the central post insulator is done by a driving lever mechanism at the

base of the post insulator and it connected to operating handle (in case of hand

operation) or motor (in case of motorized operation) of the isolator through amechanical tie rod.

Constructional features of Single Break Isolators:-

The contact arm is divided

into two parts one carries male

contact and other female contact.The contact arm moves due to

rotation of the post insulator upon

which the contact arms are fitted.

Rotation of both post insulators

stacks in opposite to each other

causes to close the isolator by

closing the contact arm. Counter

rotation of both post insulators

stacks open the contact arm and

isolator becomes in off condition. This motorized form of this type of isolators is

generally used but emergency hand driven mechanism is also provided.

Insulator

Over head electrical conductors used for transmitting electric power is mostly bare

and not covered with any insulation medium. The bare

line conductors are connected to the transmission

towers through the insulators. Insulators act as

insulating medium for flow of leakage current from

conductor to ground through tower structures. Some of

the insulating materials are Porcelain, Glass and

Steatite materials.

The porcelain insulators employed in substations are of

the post and bushing type. They serve as supports and insulation of the bus bars.

Female Contact ofIsolatorFemale Contact ofIsolator

Male Contact ofIsolatorMale Contact ofIsolator

MaleContact ofIsolator

MaleContact ofIsolator


36/44

A post insulator consists of porcelain body, cast iron cap and flanged iron base. The

hole in the cap is threaded so that the bus-bars are either directly bolted to the cap or

fixed by means of bus-bars clamp. Post insulators are available with round oval and

square flanged bases for fixing with aid of one, two or four bolts. Each base in

addition also has an earthing bolt.

A bushing insulator consists of porcelain shell body, upper and lower locating

washers used for fixing the position of bus bar or rod in shell , and mounting flange

with holes drilled for fixing bolts and supplied with an earthing bolt.

For the current rating above 2000 A, the bushings are designed to allow the main

bus-bars to be passed directly through them.

Batteries

All power plants and substations

require DC supply for protection

and control purposes and DC

supply is obtained from

secondary or storage batteries.

Storage batteries are of two types

namely lead acid and alkaline

batteries. Lead acid batteries aremost commonly used in power

stations and substations because

of their higher cell voltage and

lower cost.

Battery Chargers

As the name says battery chargers are used tocharge the storage batteries in the substation.The

interruption of DC supply to load cannot be

afforded in any circumstances so battery chargers

are employed for keeping the storage batteries

charged. Mainly there are two types of battery

chargers according to their usage :-

(i) Float Charger (ii) Boost

Charger

Float Charger


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Float charger is static type comprising of Silicon Controlled Rectifiers (SCR)

connected in three phase banks along with other necessary circuit to supply a

stabilized DC out-put. Provision is made to have step less and smooth voltage setting

in the auto mode and also for adjustment in manual mode in case the automatic

constant voltage controller fails.

Float charger have built in current limiting feature to droop the output voltage on

currents more than 100% of the rated current and it is ensured that the output voltage

of the charger across battery terminals remains below 2 Volt/cell if output current is

125% or more of the rated current.

Boost Charger

Boost charger have

adequate rating to quick

charge the battery fully

within 14 hrs. after an

emergency during

which complete DC

load is met by thebattery. Current rating

of Boost charger is

20Amps for 200AH and

30 amps for 300AH

battery sets .

Boost charger

incorporate static

components, comprising

of SCRs with

semiconductor fuses

and trip indication as in

float charger. Boost

charger, apart from its

normal constant current

operation, is also

capable of constant

voltage operation which

enables it to operate as a


38/44

float charger delivering stabilized DC output voltage within +/- 1% from no-load to

full load. In case of float charger failure, suitable electrical circuitry is provided for

this purpose.

In the constant current mode, it has a current stability of +/- 2% of the set value.

Constant current setting have step-less range from 20% to 100% of full rate current.

Further, the boost charger has a provision of manual mode of operation.

Control Room

The

control

room is

the

nervecentre of

a

substation. The various controls performed form here are the voltage adjustment,load control, emergency tripping, etc. And the equipments and the instruments

housed in a control room are synchronizing equipment, voltage regulators, relays,Fig:- A view of control room of 400 KV substation, Khedamara Bhilai (C .G.)


39/44

ammeter, voltmeters, wattmeter, kWh meters, kVARh meters, temperature gauges,

water level indicators and other appliances, as well as a mimic diagram and suitable

indicating equipment to show the opened or closed position of circuit breaker,

isolators, etc.

The location of control room in relation to other sections is also important. It shouldbe located away from the sources of noise and it should be near to the switch house

so as to save control cables used for interconnection. The control room should be

neat and clean and well ventilated, well lighted, and free from draughts. The

instruments should have scales clearly marked and properly calibrated and all the

apparatus and circuits should be labelled so that they are clearly visible.

Control Cables and conductors

The control cables and conduit

system is required for affecting

automatic controls. The controlsystem generally operates at 110 or

220 volts and the cables

employed for this purpose are

multi core cables having 2

core, 4 core, 10 core, 12 core,14

core,19 core.

The conductors are of various types but for transmission purposes ACSR

(Aluminum Conductor Steel Reinforced ) & AAAC ( All Aluminum Alloy

Conductors ) are used as they are ideal for long distance transmission of power

without major losses.

The conductors inside the control cables are categorized by the name of animals on

the scale of the maximum amount of current they can withheld. So different

conductors with their current rating are:-

Serial No. Conductor Current ( in Amperes )1. Moose Conductor 850


40/44

2. Zebra Conductor 740

3. Panther Conductor 510

4. Dog Conductor 254

5. Racoon Conductor 197

6. Rabbit Conductor 148

7. Squirrel Conductor 100

Mainly moose conductor are used in 400 KV side, zebra conductor are used in

220 KV side, panther conductor are used in 132 KV side and dog conductor

are used in 33KV side.

In 400 KV substation, Khedamara, ACSR moose conductors are used

Power Line Carrier Communication

Coupling devices are used for isolation of carrier equipment from higher

tension voltage system and to provide a low impedance path for carrier

frequency. Generally CVTs are used with LMU.

Wave traps are used to confine the carrier signals between two carrier

equipments located at the respective substation and to provide high impedance

to carrier frequency. Rated for full current.


41/44

Testing Of Transformer Oil

Breakdown Voltage Test

(BDV Test)

To assess the insulating property of

dielectric transformer oil, a sample of

the transformer oil is taken and

its breakdown voltage is measured.

The transformer oil is filled in the

vessel of the testing device. Two

standard-compliant test electrodes

with a typical clearance of 2.5 mm

are surrounded by the dielectric oil.

A test voltage is applied to the electrodes and is continuously increased up

to the breakdown voltage with a constant, standard-compliant slew rate of e.g. 2

kV/s.

At a certain voltage level breakdown occures in an electric arc, leading to a

collapse of the test voltage.

An instant after ignition of the arc, the test voltage is switched off

automatically by the testing device. Ultra fast switch off is highly desirable, as the

carbonisation due to the electric arc must be limited to keep the additional pollution

as low as possible.

The transformer oil testing device measures and reports the root mean

square value of the breakdown voltage.

After the transformer oil test is completed, the insultaion oil is stirred

automatically and the test sequence is performed repeatedly. (Typically 5

Repetitions, depending on the standard)

As a result the breakdown voltage is calculated as mean value of the

individual measurements.

Conclusion: The lower the resulting breakdown voltage, the poorer the quality of

the transformer oil.

PPM test (Karl Fisher Test)


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The instrument used for this purpose in 400 KV substation, Khedamara is MKC-520.

The MKC-520 is a Karl Fisher Coulometric Titrator, by which we can measure

micro amount of water content which exists in liquid or in solid sample material. The

measurement is easy to perform, fast in operation with its results of higher precision

and accuracy.

Principle Of Measurement

In the Karl Fisher content measurement, water

reacts with iodine and sulphur dioxide in

presence of base and alcohal.

H2O + I2 + SO2 + CH3OH + 3RN

[RNH]SO4CH3 + 2[RNH]I ------------------(1)

In the volumetric titration, iodine is added as a

titrant. In the coulometric technique, iodine is

electrolytically generated in the anolyte, which

contains iodide.

2I- I2 + 2e- ---------------------------(2)

As long as water is present in the titration cell the generated iodine reacts according

to (1). As soon as all the water reacts, excess of iodine appears in the anolyte. This

iodine is detected by the

platinum elcetrode and the iodine

production is stopped. Accordingto the Faradays law, the quantity

of iodine produced is

proportional to the current

generated. In equation (1), I2 and

H2O react with each other in 1:1

proportion.

Therefore a mole of water (18g)

is equivalent to 2 x 96500

coulombs/ 1 mg of H2O. The


43/44

total amount of moisture can thus be determined by measuring the total consumption

of eletricity.

of Transform

Maintenance of Isolator

Procedure for Replacing selection of 220 KV Selection isolator of

315 MVA ICT-2 due to red-hot state

Code taken from State load despatch centre (SLDC).

LT load of station transformer-2shifted to station transformer no.1

LT breaker of station transformer-2 switched off.

33KV side breaker switched off.

220KV side breaker of 315 MVA ICT-2switched off.

400KV main breaker and tie breaker switched off.

220KV side line isolator made open.

400KV side selection isolators are also made open.

33KV side isolator of 105 MVAunit 5,6 and 7 open.

33KV side isolator of 33/0.4KV station transformer no-2 made open.

Isolator of 33KV PT also opens.

Permit taken.

Discharge is connected to 400 KV and 220KV side.

After job has been finished the discharge is disconnected from 400KV and

220KV side.

Permit is returned.

All isolators of 400KV, 220KV, 33KV are again connected.

Again code taken from load dispatch centre to charge the transformer.

Charging is done to the transformer from 400KV side then 220KV side

then 33KV side.


44/44

Documents

Project report of transmission type eletrical substation