132 33kv substation documentation

CHAPTER 1INTRODUCTION

CHAPTER- 2

CLASSIFICATION OF SUBSTATIONS

CHAPTER-3

SINGLE LINE DIAGRAM (SLD)

CHAPTER- 4

BRIEF DISCRIPTION OF

INSTRUMENT IN THE SUBSTATION

CHAPTER- 5

PROTECTION FOR VARIOUSEQUIPMENTS

A

Mini Project Report on

OPERATION AND MAINTENANCE OF 132/33KV

SUBSTATION

Mini Project Submitted in Fulfillment of The Requirements

For The Award of The Degree

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

Submitted By

G.RAVI KUMAR 116U1A0213R.TRIVENI 116U1A0242I.VENKATESWARLU 116U1A0217G.RAJASHEKAR REDDY 116U1A0216

1

Under the guidance ofMs.R.RAMADEVI B.Tech

Asst.Professor, EEE Department

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

SreeKavitha Educational Society’sSREE KAVITHA INSTITUTE OF SCIENCE & TECHNOLOGY

(Approved by AICTE –New Delhi & Affiliated to JNTU- Hyderabad )

KRISHNAPURAM (V), MADHIRA (M), KHAMMAM-507203(T.S)

SreeKavitha Educational Society’sSREE KAVITHA INSTITUTE OF SCIENCE & TECHNOLOGY

(Approved by AICTE –New Delhi & Affiliated to JNTU- Hyderabad )

KRISHNAPURAM (V), MADHIRA (M), KHAMMAM-507203(T.S)

CERTIFICATE

This is certify that the mini project report Entitled

OPERATION AND MAINTENANCE OF 132/33KV

SUBSTATION

Is a bonafide record of work carried out by

We here by accord my approval of it as a mini project report carried out and presented in a

manner required for its acceptance in fulfillment for award of degree of Bachelor of Technology

in Electrical & Electronics Engineering in Jawaharlal Nehru Technological University,

Hyderabad.

PROJECT GUIDE HEAD OF THE DEPARTMENT

Ms.R.RAMADEVI,B.Tech Mr.G.VENKAT,M.Tech

Assistant Professor Assistant professor.

DECLARATION

We declare that the project report entitled is done by us, submitted in partial fulfillment of

the requirements for the award of the degree in BACHELOR OF TECHNOLOGY.

G.RAVI KUMAR 116U1A0213R.TRIVENI 116U1A0242I.VENKATESWARLU 116U1A0217G.RAJASHEKAR REDDY 116U1A0216

1

PLACE : KRISHNAPURAM

ABSTRACT

A substation receives electrical power from generating station via incoming transmission

line and delivers electrical power through feeders and this is used for controlling the power on

different routes. Substations are integral part of a power system and form important part of

transmission and distribution network of electrical power system.Their main functions are to

receive energy transmitted at high voltage from the generating stations, reduce the voltage to a

value appropriate for local distribution and provide facilities for switching some sub-station are

simply switching stations different connections between various transmission lines are made,

others are converting sub-stations which either convert AC into DC or vice-versa or convert

frequency from higher to lower or vice-versa.The various circuits are joined together through

these components to a bus-bar at substation. Basically, sub-station consists of power

transformers, circuit breakers, relays, isolators, earthing switches, current transformers, voltage

transformers, synchronous condensers/ capacitor banks etc.This mini project covers the

important equipments & their function in a substation. And also an attempt is made to cover

the general maintenance of substation and checks the observations to be made by shift engineer.

As a part of case study we are going to visit a 132/33Kv TRANSCO substation in

Khammam.

INDEX

CHAPTER TITTLE PAGE NO

LIST OF FIGURESLIST OF ABBREVATIONS

CHAPTER-1 INTRODUCTION1.1 Introduction of Substation ` 1

1.2 Construction of A Substation 11.2.1 Selection of Site 1

CHAPTER-2 CLASSIFICATION OF SUBSTATION2.1 According To The Requirements 32.2 According To The Constructional Features 3

CHAPTER-3 SINGLE LINE DIAGRAM3.1 Single line diagram 43.2 Feeder Circuit 4

CHAPTER-4 BRIEF DISCRIPTION OF INSTRUMENTS IN THESUBSTATION

4.1 Lightning Arrester 54.1.1 The Action of The Lightning 5

4.2 Earthing 74.2.1 In All Substations There Shall Be Provision

For Earthing The Following 74.3 Capacitor Voltage Transformers (CVT) 7

4.3.1 Specifications of CVT 94.4 Wave trap 94.5 Instrument Transformer 10

4.5.1 Current Transformer (C.T) 104.5.1.1 Basic Design Principle of C.T 114.5.1.2 Simple Line Diagram of C.T 124.5.1.3 Tests Generally To Be Conducted on C.T 124.5.1.4 Specifications of HVCT 12

4.5.1.5 Specifications of LVCT 134.5.2 Potential Transformers 14

4.5.2.1 Basic Design Principle of Voltage Transformers 154.5.2.2 Simple Line Diagram of Voltage Transformers 154.5.2.3 Tests Generally To Be Conducted on The P.T’s 154.5.2.4 General Checks For P.T 16

4.6 Circuit Breaker (C.B) 164.6.1 SF6 Circuit Breaker 184.6.2 Vaccum Circuit Breaker 184.6.3 Name Plate Details of 132KV SF6 C.B 184.6.4 Name Plate Details of 33KV Vaccum C.B 19

4.7 Bus 194.8 Transformer 20

4.8.1 Basic Principle 204.8.2 Induction Law 214.8.3 Specifications of 132KV/33KV Auto T/F 23

4.9 Capacitor Bank Attached To The Bus 234.9.1 Capacitor Control is Usually Done To Achive

The Following Goals 24

CHAPTER-5 PROTECTION FOR VARIOUS EQUIPMENTS5.1 Transformer Protection 255.2 Feeder Protection 255.3 Important Points To Be Kept In View While Laying 26

Out The Substation

CONCLUSION 27

REFERENCES 28

LIST OF FIGURESFig:1.2.1 Diagram of Substation

Fig.4.1.1.1 (i) Surge Diverter

(ii)Characteristics of The Non Linear ResisterFig: 4.1.1.2 Lightning Arrester

Fig: 4.3.1 Circuit Diagram of CVT.

Fig: 4.3.2 Capacitor Voltage Transformer.

Fig:4.4.1 Wave Trap

Fig:4.5.1.1.1 Current Transformer

Fig: 4.5.1.2.1 Line Diagram of C.T

Fig: 4.5.2.1.1 Potential Transformer.

Fig: 4.5.2.2.1 Line Diagram of V.T

Fig: 4.6.1 Circuit Breaker

Fig: 4.8.1 Electrical Transformer.

Fig: 4.8.1.1 Ideal Transformer.

Fig: 4.8.2.1 Mutual Induction.

Fig: 4.8.2.2 Three Phase 50MVA Auto Transformer.

Fig: 4.9.1 Capacitor Bank In The Distribution System.

Fig: 4.9.1.1 Reactive Losses.

LIST OF ABBREVIATIONS

EHV –Extra High Voltage

SLD – Single Line Diagram

PT – Potential Transformer

CT – Current Transformer

HVCT - High Voltage CT

LVCT – Low Voltage CT

CVT – Capacitor Voltage Transformer

LA – Lightening Arrestors

ES - Earth Switches

CB – Circuit Breaker

HV side – High Voltage Side

LV side – Low Voltage Side

PLCC - Power Line Carrier Communication

OLTC –On load Tap Changer

HG Fuse -Horn Gap Fuse

OTT –Oil Temperature Indicator

WTI – Winding Temperature Indicator

IDMT Characteristics – Inverse Definite Minimum Time Characteristics.

OPERATION AND MAINTENANCE OF 132/33KV SUBSTATION

DEPT OF EEE, SKIT. Page 1

1.1 INTRODUCTION OF SUBSTATION

The present-day electrical power system is A.C. i.e. electric power is generated,

transmitted and distributed in the form of alternating current. It is delivered to the

consumers through a large network of transmission and distribution. At many places in

the line of the power system, it may be desirable and necessary to change some

characteristic (e.g. voltage, A.C. to D.C., frequency, Power factor etc.) of electric supply.

This is accomplished by suitable apparatus called sub-station. For example, generation

voltage (11KV or 6.6KV) at the power station is stepped up to high voltage (say

132KV or 220KV) for transmission of electric power. The assembly of apparatus (e.g.

transformer etc.) used for this purpose is the sub-station. Similarly, near the consumer’s

localities, the voltage may have to be stepped down to utilization level. This job is again

accomplished by a suitable apparatus called ‘substation.

1.2 CONSTRUCTION OF A SUBSTATION

At the time of constructing a substation, we have to consider some factors which

affect the substation efficiency like selection of site.

1.2.1 Selection of Site

Main points to be considered while selecting the site for EHV Sub-Station are as

follows:

The site chosen should be as near to the load centre aspossible.

It should be easily approachable by road or rail for transportation of

equipments.

Land should be fairly levelled to minimize development cost.

The sub-station site should be as near to the town / city but should be clear

of public places, aerodromes, and Military / police installations.



The land should be have sufficient ground area to accommodate substation

equipments, buildings, staff quarters, space for storage of material, such as store

yards and store sheds etc. with roads and space for future expansion.

Set back distances from various roads such as National Highways,State

While selecting the land for the substation preference to be given to the

Govt. land over Private land.

Fig:1.2.1.1 Diagram of Substation



There are several ways of classifying sub-stations. However, the two most important

ways of classifying them are according to (1) service requirement and (2) constructional

features.

2.1 ACCORDING TO THE REQUIREMENT

A sub-station may be called upon to change voltage level or improve power factor or

convert A.C. power into D.C. power etc. According to the service requirement, sub-stations

may be classified into:

1 Transformer sub-stations

2 Switching sub-stations

3 Power factor correction sub-stations

4 Frequency changer sub-stations

5 Converting sub-stations

6 Industrial sub-stations

2.2 ACCORDING TO THE CONSTRUCTIONAL FEATURES

A sub-station has many components (e.g. circuit breakers, switches, fuses, instruments

etc.) which must be housed properly to ensure continuous and reliable service. According to

constructional features, the sub-stations are classified as

Indoor sub-station

2 Outdoor sub-station

Underground sub-station

Pole-mounted sub-station



3.1 SINGLE LINE DIGRAM

A Single Line Diagram (SLD) of an Electrical System is the Line Diagram of the

concerned Electrical System which includes all the required electrical equipment connection

sequence wise from the point of entrance of Power up to the end of the scope of the mentioned

Work. As in the case of 132KV Substation, the SLD shall show Lightening Arrestor,

C.T/P.T Unit, Isolators, Protection and Metering P.T & C.T. Circuit Breakers, again Isolators

and circuit Breakers, Main Power Transformer, all protective devices/relays and other special

equipment like CVT, GUARD RINGS, etc as per design criteria. And the symbols are

shown below. There are several feeders enter into the substation and carrying out the

power. As these feeders enter the station they are to pass through various instruments.

3.2. FEEDER CERCUIT

1 Lightening Arrestors2 CVT3 Wave trap4 Isolators with Earth Switch

5 Current Transformer6 Circuit Breaker7 Feeder Bus Isolator

8 BUS9 Potential Transformer in the Bus with a Bus Isolator.



4.1 LIGHTENING ARRESTERS

Lightening arresters are the instruments that are used in the incoming feeders so that to

prevent the high voltage entering the main station. This high voltage is very dangerous to the

instruments used in the substation. Even the instruments are very costly, so to prevent any

damage lightening arresters are used. The lightening arresters do not let the lightening to fall

on the station. If some lightening occurs the arrestors pull the lightening and ground it to the

earth. In any substation the main important is of protection which is firstly done by these

lightening arrestors. The lightening arresters are grounded to the earth so that it can pull the

lightening to the ground.

These are located at the entrance of the transmission line in to the substation and as near

as possible to the transformer terminals.

The lightning arresters or surge diverters provide protection against such surges. A

lightning arrester or a surge diverter is a protective device, which conducts the high voltage

surges on the power system to the ground.

Fig.4.1.1.1 (i) Surge Diverter(ii)Characteristics of The Non Linear Resister



Fig: 4.1.1.2 Lightning Arrester

4.1.2 The Action of The Lightning Arrester or Surge Diverter is as Under Under normal operation, the lightning arrester is off the line i.e. it conducts no current

to earth or the gap is non-conducting.

On the occurrence of over voltage, the air insulation across the gap breaks down and

an arc is formed providing a low resistance path for the surge to the ground. In

this way, the excess charge on the line due to the surge is harmlessly conducted through

the arrester to the ground instead of being sent back over the line.

It is worthwhile to mention the function of non-linear resistor in the operation ofarrester. As the gap sparks over due to over voltage, the arc would be a short circuit onthe power system and may cause power-follow current in the arrester. Since thecharacteristic of the resistor is to offer low resistance to high voltage (or current), itgives the effect of short circuit. After the surge is over, the resistor offers high resistanceto make the gap non conducting

The LA voltage rating corresponding to the system voltages are indicated belowRated system

Voltage (KV)

Highest system

Voltage (KV)

Arrester rating in KV

Effectively earthed systems

11 12 9

33 36 30

66 72.5 60

132 145 120/132 (latex)

220 245 198/216 (latex)

400 420 336

Table:4.1.2.1 LA Voltage Rating



4.2 EARTHING

The earthing practice adopted at generating stations, sub-stations and lines should be in

such a manner as to provide in units of ohms

Safety to personnel

Minimum damage to equipment as a result of flow of heavy fault currents

Improve reliability of power supply

Large sub-stations- 1

Small sub-stations-2

Power stations -0.5

Distribution transformer stations- 5

4.2.1 In All Sub-Stations There Shall be Provision For Earthing The Following

The neutral point of earth separate system should have an independent earth, which

in turn should be interconnected with the station grounding mat

Equipment frame work and other non-current carrying parts.

All extraneous metallic frame work not associated with equipment (two connections)

The earth conductor of the mat could be buried under earth to economical depth of

burial of the mat 0.5 meters.

4.3 CAPACITOR VOLTAGE TRANSFORMER (CVT)

A capacitor voltage transformer (CVT) is a transformer used in power systems tostep-down extra high voltage signals and provide low voltage signals either for measurementor to operate a protective relay

These are high pass Filters (carrier frequency 50KHZ to 500 KHZ) pass carrier

frequency to carrier panels and power frequency parameters to switch yard. In its most basic

form the device consists of three parts: two capacitors across which the voltage signal issplit, an

inductive element used to tune the device and a transformer used to isolate and further step-

down the voltage.



Fig: 4.3.1 Circuit Diagram of C.V.T

The device has at least four terminals, a high-voltage terminal for connection to the

high voltage signal, a ground terminal and at least one set of secondary terminals for

connection to the instrumentation or protective relay. CVTs are typically single-phase devices

used for measuring voltages in excess of one hundred KV where the use of voltage transformers

would be uneconomical. In practice the first capacitor, C1, is often replaced by a stack of

capacitors connected in series. This results in a large voltage drop across the stack of

capacitors, that replaced the first capacitor and a comparatively small voltage drop across the

second capacitor, C2, and hence the secondary terminals.

Fig: 4.3.2 Capacitor Voltage Transformer.



4.3.1 Specifications of CVT

CVT type : CVEB/245/1050

Weight : 665 kg

Total output simultaneous : 250 VA

Output maximum : 750 VA at 50O C

Rated voltage : A-N, 220/√3

Highest system voltage : A-N, 245/√3Rated frequency : 50Hz

Nominal intermediate voltage : A1-N, 20/√3 KV

Voltage factor : 1.2Cont. 1.5/30 sec

‘HF’ capacitance : 4400pF +10% -5%

Primary capacitance C1 : 4840pF +10% -5%

Secondary capacitance C2 : 48400 pF +10%-5%

Voltage ratio : 220000/√3/ 110/√3/110-110/√3

Voltage : 110/√3 110-110/√3

Burden : 150 100

Class : 0.5

4.4 WAVE TRAP

Wave trap is an instrument using for trapping of the wave. The function of this

wave trap is that it traps the unwanted waves. Its shape is like a drum. It is connected to the

main incoming feeder so that it can trap the waves which may be dangerous to the

instruments in the substation. Generally it is used to exclude unwanted frequency components,

such as noise or other interference, of a wave.

Note: Traps are usually unable to permit selection of unwanted or interfering signals.



Line trap also is known as Wave trap. What it does is trapping the high frequency

communication signals sent on the line from the remote substation and diverting them to the

telecom/tele protection panel in the substation control room through coupling capacitor.

Fig:4.4.1 Wave Trap

This is relevant in Power Line Carrier Communication (PLCC) systems for

communication among various substations without dependence on the telecom company

network. The signals are primarily tele protection signals and in addition, voice and data

communication signals. The Line trap offers high impedance to the high frequency

communication signals thus obstructs the flow of these signals in to the substation bus bars. If

these are not present in the substation, then signal loss is more and communication will be

ineffective/probably impossible.

4.5 INSTRUMENT TRANSFORMERS

“Instrument Transformers are defined as the instruments in which the secondary current or

voltage is substantially proportional to the primary current or voltage and differs in phase from

it by an angle which is approximately zero for an appropriate direction of connection”.

Direct measurement of current or voltage in high voltage system is not possiblebecause of high values and insulation problems of measuring instruments they cannot bedirectly used for protection purposes.

Instrument transformers are of two types:

Current Transformers

Voltage Transformers

4.5.1 Current Transformers:Current transformer is a current measuring device used to measure the currents in

high voltage lines directly by stepping down the currents to measurable values by means

of electromagnetic circuit.



4.5.1.1 Basic Design Principle of Current Transformers

The basic principle induced in designing of current transformers is

Primary ampere turns = Secondary ampere turns

Ip Np = Is Ns

Where, Ip - Primary current

Np - Primary Winding Turns

Is - Secondary Current; Ns - Secondary Winding Turn

Ampere turns plays very important role in designing current transformers.

Current transformers must be connected in series only.

Current transformer has less no of turns in primary and more no of turns in

secondary.

The secondary current is directly proportional to primary current.

The standards applicable to CT's are IEC-60044-1 and IS – 2705.

Fig:4.5.1.1.1 Current Transformer



4.5.1.2 Simple Line Diagram of Current Transformer

The line diagram of a current transformer contains different components:

S

Fig: 4.5.1.2.1 Line Diagram of C.T

4.5.1.3 Tests generally to be conducted on CT

Insulation resistance values (IR values): Primary to earth, primary to

secondary core1, primary to secondary core2, core1 to earth, core2 to earth and

core1 to core2. Primary to earth and primary to secondary cores are to be checked

with 5KV motor operated insulation tester (megger) and secondary to earth values

are to be checked with 1000V insulation tester or preferably with 500V insulation

tester.

Ratio test: Primary injection test is to be conducted for this purpose

TAN-DELTA test: on 132KV CTs and above

Secondary and lead resistance check

Secondary injection check

Primary injection check

4.5.1.4 Specifications of HVCT

Type : IT-245

Frequency : 50 Hz

H.S.V : 245 KV

BIL : 460/1050KV Oil

weight : 360kgs

Total weight : 1250kgs



RATIO800-600-400/1-1-1-1-1

CORE NUMBER 1 2 3 4 5RATED PRIMARY

CURRENT (A)800

RATEDSECONDARYCURRENT(A)

1 1 1 1 1

OUTPUT(VA) -------- ------------------

----- ------- - 30

ACCURACY CLASS PS PS PS PS 0.5I.S.F/A.L.F ---- --- --- --- <=5

TURN RATIO 2/1600 1200 800

RCT at 75 C AT 800/1(ohms)

6 6 6 ---

Table: 4.5.1.4.1 Specifications of HVCT.

At the rate of LV (132KV) side we can use 1:3 core CT. The specifications of LVCT

are given below:

4.5.1.5 Specifications of LVCT

Type : IT-145

Frequency : 50 Hz

HSV/NSV : 145/132 KV

BIL : 650/275 KV Oil

weight : 75Kg

Total weight : 550Kg



RATIO500/1-1, 0.66-1

CORE NUMBER 1 2 3

RATED PRIMARY

CURRENT (A)500

PRIMARY &

SECONDARY

CONNECTION

500/1 500/1 500/0.66 500/1

1s1-1s2 2s1-2s2 2s1-2s3 3s1-3s2

RATED SECONDARY

CURRENT(A)1 1 0.66 1

OUTPUT(VA) 20 ------- ------------ 20

ACCURACY CLASS 5p PS 0.2

I.S.F/A.L.F 20 -------- --------- <=5

Rct at 75o C (Ohms) -------- <=5 --------- -------------

Table:4.5.1.5.1 Specifications of LVCT

NOTE

CT secondary circuit and PT primary should never be open circuited. It is

vulnerable to the CT/PT

CT primary circuit and PT secondary should never be short circuited.

4.5.2 Potential Transformers (PT)

An instrument transformer in which the secondary voltage, in normal conditions of use,

is substantially proportional to the primary voltage and differs in phase from it by an angle

which is approximately zero for an appropriate direction of the connections.



4.5.2.1 Basic Design Principle of Voltage Transformer’s

The basic principle involved in the designing of Voltage Transformer is

Voltage Ratio = Turns Ratio

VP / VS = NP / NS

Thus NS VP = NP VS

As heavy primary voltages will be reduced to low secondary voltages, it will have moreturns in the primary & less turns in the secondary. It must always be connected in parallel only.Even if we connect it directly from high voltage to earth, it is not going to be a short circuit as itsprimary winding has very high resistance. Its core is a set of assembled laminations. It operatesat constant flux density. The standards are IEC – 600044 – 2 and IS – 3156.

Fig: 4.5.2.1.1 Potential Transformer.

4.5.2.2 Simple Line Diagram of Voltage Transformer

Fig: 4.5.2.2.1 Line Diagram of VT.

4.5.2.3 Tests generally to be conducted on the PTs

Insulation resistance values (IR values): primary to earth, primary to

secondary core-1, primary to secondary core-2, core1 to earth, core 2 to earth

and core-1 to core-2. These values are to be checked with 1000V insulation

tester (megger) or preferably with 500V insulation tester.



Ratio Test: By applying single phase voltage across primary the voltage

induced in the secondary winding is to be measure. This is approximately equal to

voltage applied in the primary winding or voltage ratio of the PT.

Polarity test: at the time of commissioning (at least on the PTs connected to

revenue meters)

PT secondary injection check

4.5.2.4 General checks for PT

Mechanical alignment for PT power jaws

PT primary winding star earthing Tightness of all connections

Primary/secondary fuse ratings

PT specifications

In PTs no of secondary cores is 1 or more than 1 based on the requirement. Generally

in 11KV or 33KV bus PTs, there is one secondary winding which is used both for protection

and metering and in 132KV and above, there are two secondary cores. First core is of metering

core with 1.0 or 0.5 or 0.2 accuracy classes. This will be used metering, directional over current

protection and distance protection.

4.6 CIRCUIT BREAKER

The circuit breakers are used to break the circuit if any fault occurs in any of the

instrument. These circuit breaker breaks for a fault which can damage other instrument in the

station. For any unwanted fault over the station we need to break the line current. This is only

done automatically by the circuit breaker.

Operation mechanism function,

Arc quenching function.



Fig: 4.6.1 Circuit Breaker

various operating mechanisms

1 Spring charge mechanism,2 Pneumatic mechanism,3 Hydraulic Mechanism.

Arc quenching medium

1 Bulk oil (called bulk oil circuit breakers-BOCB)

Minimum oil (called minimum oil circuit breakers-MOCB)

Natural air (called air circuit breakers-ACB) (415v)

Forced air (called air blast circuit breaker-ABCB)

Vacuum (called vacuum circuit breaker-VCB)

SF6 gas (called Sulphur Hexafluoride-SF6 gas CB)

The present trend is up to 33KV, VCBs are preferred and beyond 33KV, SF6 gas

circuit breakers are preferred.

There are mainly two types of circuit breakers used for any substations. They are

(a) SF6 circuit breakers,

(b) Vacuum circuit breakers.



4.6.1 SF6 Circuit Breakers

Sulphur hexafluoride (SF6) is an inert, heavy gas having good dielectric and arc

extinguishing properties. The dielectric strength of the gas increases with pressure and is more

than the dielectric strength of oil at 3 kg/cm2. SF6 is now being widely used in electrical

equipment like high voltage metal enclosed cables; high voltage metal clad switchgear,

capacitors, circuit breakers, current transformers, bushings, etc. The gas is liquefied at certain

low temperature, liquidification temperature increases with the pressure.

Some of the properties of SF6 are,

Very high dielectric strength

High thermal and chemical inertia

Superior arc extinguishing capability Low decomposition by arcing

4.6.2 Vacuum Circuit Breakers

Vacuum type of circuit breakers is used for small KV rated stations below 33KV.

They are only used in low distribution side.

4.6.3 Name Plate Details of 132KV SF6 CB

Type : 200-SFM-40A

Rated Voltage : 145KV

Lightining Impulse Withstand : 650KV(Peak)

Rated Frequency : 50HZ

Normal Current : 1600A

Rated Short Circuit Breaking Current

Symmetrical : 31.5KAAsymmetrical : 37.2KA

Rated Short Circuit Making Current : 80KA(Peak)

Out-Of-Phase Breaking Current : 7.9KA

Rated Break Time : 60ms(3 Cycles)

Rated Short Time Current : 40KA For 3 Sec



Operating Sequence : 0-0.03s-C0-3min-CO

Total Mass OF SF6 Gas : 8.7kg

SF6 Gas Pressure AT 20c,1013hpa : 6.3bar

Total Mass Of The Circuit Breaker : 1300kg

Reference Standard : IEC-56

4.6.4 Name Plate Details of 33KV Vacuum CB

Voltage : 36KV

Frequency : 50HZ

Normal Current : 800A

SYM Breaking Capacity : 25KA

Short Time Current : 25KA

Duration : 3sec

Making Capacity : 63KA(peak)

P.F Withstand : 70KV

Impulse : 170KV(peak)

Shunt Trip coil : 220VDC

Spring RELCoil : 220VDC

Total Weight : 2000kg

Operating Sequence : 0-3MIN-CO-3MIN-CO

Type : VN36 3AF

4.7 BUS

The bus is a line in which the incoming feeders come into and get into the instruments

for further step up or step down. The first bus is used for putting the incoming feeders in la

single line. There may be double line in the bus so that if any fault occurs in the one the other

can still have the current and the supply will not stop. The two lines in the bus are separated by

a little distance by a conductor having a connector between them. This is so that one can work

at a time and the other works only if the first is having any fault.



4.8 TRANSFORMERS

Transformers come in a range of sizes from a thumbnail-sized coupling transformer

hidden inside a stage microphone to huge units weighing hundreds of tons used to

interconnect portions of national power grids. All operate with the same basic principles,

although the range of designsis wide. While new technologies have eliminated the need for

transformers in some electronic circuits, transformers are still found in nearly all electronic

devices designed for household ("mains") voltage. Transformers are essential for high

voltage power transmission, which makes long distance transmission economically practical.

Fig: 4.8.1 Electrical Transformer.

4.8.1 Basic Principle

The transformer is based on two principles: firstly, that an electric current can produce

a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil

of wire induces a voltage across the ends of the coil (electromagnetic induction).

Changing the current in the primary coil changes the magnetic flux that is developed.

The changing magnetic flux induces a voltage in the secondary coil.



Fig: 4.8.1.1 Ideal Transformer.

An ideal transformer is shown in the adjacent figure; Current passing through the

primary coil creates a magnetic field. The primary and secondary coils are wrapped

around a core of very high magnetic permeability, such as iron, so that most of the magnetic

flux passes through both primary and secondary coils.

4.8.2 Induction law

The voltage induced across the secondary coil may be calculated from Faraday's

law of induction, which states that, where VS is the instantaneous voltage, NS is the number

of turns in the secondary coil and Φ equals the magnetic flux through one turn of the coil.

If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the

product of the magnetic field strength and the area A through which it cuts. The area is

constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic

field varies with time according to the excitation of the primary.

Fig: 4.8.2.1 Mutual Induction.



Since the same magnetic flux passes through both the primary and secondary coils in an

ideal transformer, the instantaneous voltage across the primary winding equals Taking the ratio

of the two equations for VS and VP gives the basic equation for stepping up or stepping down

the voltage Ideal power equation The ideal transformer as a circuit element.

If the secondary coil is attached to a load that allows current to flow, electrical power is

transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is

perfectly efficient; all the incoming energy is transformed from the primary circuit to the

magnetic field and into the secondary circuit. If this condition is met, the incoming electric

power must equal the outgoing power.

Giving the ideal transformer equation Transformers are efficient so this formula is a

reasonable approximation. If the voltage is increased, then the current is decreased by the same

factor. If an impedance ZS is attached across the terminals of the secondary coil, it appears to

the primary circuit to have an impedance of ZS = (VS/IS).

Fig: 4.8.2.2 Three Phase 50MVA Auto Transformer.



4.8.3 Specifications of 132KV/33KV Auto Transformer

Rated MVA : 50MVANo of phases : 3Insulation level : HV LI 900 AC 395

: HVN LI 95 AC 38IV LI 550 AC 230LV LI 170 AC 70

Type of cooling : ONAN DNAFRated MVA : 75 100Rated KV at no load : HV 220KV --

: IV 132KV --LV 11KV --

Line Amperes : HV 196.8 262.4IV 328.0 437.4LV 1299.0 1732.1

Temperature Rise oC : Top oil - 50oCAvg.WDG : - 55OCImpedance volts : HV-IV 7.667 10.222Normal Tap conditions) : HV-LV 24.55 32.72

: IV-LV 17.69 23.59

4.9 CAPACITOR BANK ATTACHED TO THE BUS

The capacitor banks are used across the bus so that the voltage does not get down till at

the require place. A capacitor bank is used in the outgoing bus so that it can maintain the

voltage level same in the outgoing feeder.

Fig: 4.9.1 Capacitor Bank In The Distribution System.



4.9.1 Capacitor Control Is Usually Done To Achieve The Following Goals

Reduce losses due to reactive load current;

Reduce KVA demand, decrease customer energy consumption,

Improve voltage profile, and increase revenue.

Indirectly capacitor control also results in longer equipment lifetimes because

of reduced equipment stresses.

Experience shows that switched feeder capacitors produce some of the fastest returns

on equipment investment Sources of Energy Loss. Energy losses in transmission lines and

transformers are of two kinds: resistive and reactive. The former are caused by resistive

component of the load and cannot be avoided. The latter, coming from reactive component of

the load, can be avoided.

Fig: 4.9.1.1 Reactive Losses.



5.1 TRANSFORMER PROTECTION

Station Transformer: HG Fuse protection on HV side and fuse protection on LV side

and Vent pipe.

Power transformers up to 7.5MVA:

HV side: O/L & Directional E/L protection with highest element in O/L relays.

LV side: O/L & E/L protection Buchholz Relay OLTC Buchholz RelayOTI and WTI

Power transformers from 8.0MVA and above: HV side O/L & Directional E/L

protection with high set element in O/L relays. LV side O/L & E/L

protection: differential protection Buchholz Relay OLTC Buchholz Relay OTI, WTI

and PRV.

Power transformers from 31.5MVA and above: Over flux protection & LV WTI in

addition to protection.

5.2 FEEDER PROTECTION

33KV feeders: Non directional O/L & E/L protection with highest and IDMTcharacteristics.

132KV feeders: Main protection: Distance protection. Back up protection: DirectionalO/L & E/L protection.

220KV feeders: Main-1 protection: Distance protectionMain-2protection: Distanceprotection, LBB protection, pole discrepancyRelay.



5.3 IMPORTANT POINTS TO BE KEPT IN VIEW WHILE LAYINGOUT THE SUBSTATION

Substations are important part of power system. The continuity of supply depends to a

considerable extent upon the successful operation of sub-stations. It is, therefore, essential to

exercise utmost care while designing and building a substation.

The following are the important points which must be kept in view while laying out a

substation:

It should be located at a proper site. As far as possible, it should be located at thecentre of gravity of load.

It should provide safe and reliable arrangement. For safety, consideration must begiven to the maintenance of regulation clearances, facilities for carrying out repairsand maintenance, abnormal occurrences such as possibility of explosion or fire etc.For reliability, consideration must be given for good design and construction,the provision of suitable protective gear etc.

It should be easily operated and maintained.

It should involve minimum capital cost



CONCLUSION

Transmission and distribution stations exist at various scales throughout a power

system. In general, they represent an interface between different levels or sections of the

power system, with the capability to switch or reconfigure the connections among various

transmission and distribution lines.

The major stations include a control room from which operations are coordinated.

Smaller distribution substations follow the same principle of receiving power at higher

voltage on one side and sending out a number of distribution feeders at lower voltage

on the other, but they serve a more limited local area and are generally unstaffed.

The central component of the substation is the transformer, as it provides the effective

in enface between the high- and low-voltage parts of the system. Other crucial

components are circuit breakers and switches. Breakers serve as protective devices that

open automatically in the event of a fault, that is, when a protective relay indicates

excessive current due to some abnormal condition. Switches are control devices that can

be opened or closed deliberately to establish or break a connection.

An important difference between circuit breakers and switches is that breakers are

designed to interrupt abnormally high currents (as they occur only in those very

situations for which circuit protection is needed), whereas regular switches are

designed to be operable under normal currents. Breakers are placed on both the high- and

low-voltage side of transformers. Finally, substations may also include capacitor banks to

provide voltage support



REFERENCES

[1] Principles of Power Systems by V.K. Mehtha

[2] Electrical Power Systems by C.L. Wadhwa

[3] Power System Engineering by ML. Soni

[4] Electrical & Electronics Measurement &Instruments by A.K.Sawhney Dhanpat Rai