220KV SANTEJ SUB-STATION, GETCO

A SUMMER INTERNSHIP REPORT

Submitted by

DEDUN ROHITKUMAR RAMESHBHAI

220170109027

In partial fulfillment for the award of the degree of

BACHELOR OF ENGINEERING

in

Electrical Engineering Department

Vishwakarma Government Engineering College Chandkheda, Ahmedabad

Gujarat Technological University, Ahmedabad

1
 DEPARTMENT OF ELECTRICAL ENGINEERING

VISION

To produce comprehensively trained, socially responsible and innovative electrical

graduates to contribute to the society

MISSION

M1: To develop well equipped laboratories and infrastructure for conducive

learning M2: To produce competent and disciplined electrical engineers to serve the

nation.

M3: To help in building national capabilities for excellent energy management and to
explore non conventional energy sources.

M4: To produce electrical engineers with an attitude to adapt themselves to

changing technological environment

M5: To enhance entrepreneurship skills through start-ups

2
 VISHWAKARMA GOVERNMENT ENGINEERING COLLEGE CHANDKHEDA

Department of Electrical Engineering

CERTIFICATE

This is to certify that Mr. DEDUN ROHITKUMAR RAMESHBHAI (En. No: 220170109027) Sem:-6

B.E (Electrical Engineering), has completed the Summer Internship/Industrial training entitled “220KV

SANTEJ SUB-STATION, GETCO” from 02-07-2025 to 16-07-2025 (Total no of Weeks: 2 ) at the

GETCO under my guidance and the report has been submitted to Electrical Engineering Department.

Prof(Dr). S. N. Pandya Prof. D.J.Vaghela

Head of the Internal Guide
department

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 [Company/Industry letterhead]

No. Date:

TO WHOM IT MAY CONCERN

This is to certify that, Mr.DEDUN ROHITKUMAR RAMESHBHAI Enrollment No:220170109027

Student of Electrical Engineering, Vishwakarma Government Engg. College Chandkheda, has successfully

completed a two week Internship in the field of 220 KV SANTEJ SUB-STATION,GETCO during the

period of _02-07-2025 TO 16-07-2025.During the period of his internship program with us, He had been

exposed to different processes and found sincere and hardworking.

Authorised Signature with stamp Mentor Signature.

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 Acknowledgement

I am very thankful for giving me the opportunity to undertake my

internship training at The prestigious “220KV sub station GETCO”. It
was a very good Learning experience for me to have at this site.

First, I would like to thank Head of The Department Dr. S.N. Pandya of
Vishwakarma Government Engineering College, Ahmedabad for giving
permission to commence this Internship.

Further, I would like to express my sincere gratitude to my Industrial

Mentor Mr. T.K.Patel for continuously guiding me at the company and
dispel all my doubts with Patience.

Also, I am very obliged to my Internal Mentor Prof. D.J.Vaghela for

helping Me throughout my internship and giving me a necessary
suggestions and advices along with Their valuable coordination. Without
their continuous support it would not have been Possible to complete
my internship.

I own my wholehearted thanks and appreciation to the entire staff of

the company for their Cooperation and assistance during my internship.
I also thank my parents, friends, and all the members of the family for
their precious support And encouragement which they had provided in
the completion of my work.

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 Abstract

The internship provided hands-on experience in the operation, maintenance, and

management of high-voltage 220KV electrical system. Key responsibilities included
monitoring electrical parameters, performing routine maintenance, and assisting
in troubleshooting and repair activities.

I acquired in-depth knowledge of the key components such as transformers, circuit

breakers, busbars, isolators, current transformer, lightening arresters, potential
transformer and control and relay panels.

Through collaboration with experienced engineers, the internship enhanced my

understanding of power system dynamics, substation automation, and the critical
role of substations in the electrical grid.

This experience has significantly contributed to my professional development in

electrical engineering and prepared me for a future career in the power sector.

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 Table of content
Acknowledgement 5

Abstract 6

1 Introduction 10
1.1 About Company

2 Single Line Diagram 13

2.1 220KV Side
2.2 66KV Side

3 Switchyard 15
3.1 Lightening Arrester
3.2 Isolator
3.3 Circuit Breaker
3.4 Current Transformer
3.4.1 Current Transformer Tests
3.5 Potential Transformer

4 Power Transformers 29
4.1 Cooling Mechanism
4.1.1 Oil natural air natural
4.1.2 Oil natural air forced
4.1.3 Oil forced air forced
4.2 Transformer Detail
4.3 Important Part Of Power Transformer
4.3.1 OLTC
4.3.2 PRV
4.3.3 Buchholz relay
4.3.4 Breather
4.3.5 NIFPS

5 Battery Room 37

6 Control Room 39
6.1 Types Of Panels In Substation

7 Protection systems 43
7.1 Distance protection
7.2 Busbar protection

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 7.2 Protection of transformer
7.2.1 Differential protection
7.2.2 Restricted earth fault
7.2.3 Backup protection
7.2.4 Buchhloz relay
7.2.5 Thermal protection
7.2.6 Pressure relief valve

8 Equipment testing 53
8.1 Lightening arrester testing
8.2 Circuit breaker testing
8.3 Battery testing
8.4 Transformer testing

9 Maintenance and LCP 59

10 Conclusion 60

Reference 61

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 List of figures
Figure 1.1 overview of industry 10

Figure 2.1 single line diagram of 220KV side 13

2.2 single line diagram of 66KV side 14
Figure 3.1 switchyard 15
3.2 lightening arrester 17
3.3 metal oxide lighting arrrester 18
3.4 isolator 19
3.5 vaccume circuit breaker 20
3.6 SF6 circuit breaker 20
3.7 current transformer 22
3.8 knee point voltage test 26
3.9 tan delta test 27
3.10 potential transformer 28

Figure 4.1 transformer 32

4.2 OLTC 32
4.3 pressure relief valve 33
4.4 buchhloz relay 34
4.5 breather 35
4.6 NIFPS 36

Figure 5.1 battery room 38

Figure 6.1 control room 40
6.2 transformer panel 41
6.3 bus coupler panel 42
Figure 7.1 distance protection 43
7.2 bus bar protection 44
7.3 differential protection 46
7.4 restricted earth fault 47
7.5 backup protection 48
7.6 buchhloz relay 49
7.7 thermal protection 50
7.8 PRV 52

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 Chapter 1 : Introduction
1.1 Overview of industry

( Figure 1.1)

Gujarat Energy Transmission Corporation Limited is an electrical power transmission

company in Gujarat. It was set up in may 1999 and is registered under the companies
act of 1956. The company was promoted by the erstwhile Gujarat electricity
board(GEB) as its wholly subsidiary in the context of liberalization and as a part of
effort towards restructuring of the power sector. The company is now a subsidiary of
Gujarat Urja Vikas Nigam, the successor company to the GEB.

The central government of india passed the electricity act in 2003, 3hile the Gujarat
government approved the Gujarat electricity industry act in 2003. And other items of
former Gujarat electricity board to new entities. As a result GEB divides into seven
firms with operational responsibility for trading, generation, transmission and
distribution as of 1 april 2005.

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Company type Public sector utility

Industry power
predecessor Gujarat Electricity
Board(GEB)
Founded 1999
Headquarter Vadodara
Area reserved Gujarat
Service Power transmission
Number of employees 13,000+

Voltage No. of Transmission line

system substations (km)
(kv)

400 16 6,096

220 105 20,478

132 57 5,566

66/11 1846 33,468

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Chapter 2 : Single line diagram

12
 Chapter 3 : Switchyard

 Substations are important components of electrical infrastructure that ensure

reliable electricity for customers. They perform several functions, including:
 Switching: Connecting and disconnecting lines, equipment, and circuits
or lines from a system
 Voltage transformation: Changing alternating current (AC) voltages from one
level
(220kV) to another (66kV), or transforming high voltage electricity from
the transmission system to lower voltage electricity
 Current conversion: Changing AC to direct current (DC) or DC to AC (PLCC
Room)

 Protection:- power system protection schemes such as,

○ Differential:- 3 types of differential protection schemes are used
in this substation.
■ Line differential:- optical fiber cables transfer the data
through long distances, and then the fault is detected
accordingly.

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 ■ Bus bar differential:- detects the fault within the busbar
protected zone.
■ Transformer differential:- protects the transformer in case of
faults within the transformer or the differential protection
zone.
○ Distance protection:- Mho relays are used to detect the faults
along the zones decided by the relay CT and PT are used for the
measurement. As this method of protection has a large time delay
hence the line differential protection system is also used to
protect the system.
○ REF (restricted earth fault):- during an internal fault, the neutral
current transformer only carries the unbalanced fault current,
and operation of the Restricted Earth Fault Relay takes place.

 There is a series of protective equipments connected through the line

before the power equipments (busbar & transformer) the series is as
follows:
 L.A. (lightening arrester)
 Isolator
 Circuit breaker
 Current transformer
 Potential transformer

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3.1 Lighting Arrester

Figure 4.2

 A lightening arrester is a device that protects electrical equipment and

other structure from lightening strike. It’s a key component of a lightening
protection system and is typically installed at the highest point of a
structure. The arrester creates a low resistance path for lightening
charges to flow into the ground, safely grounding them and protecting the
electrical systems.
 It is placed first in the sub-station to prevent damage to other equipment
during a lightening surge.
 Generally in sub-station we use metal oxide lightning arrester.

3.1.1 Metal oxide lighting arrester

 The arrester which uses zinc oxide semiconductor as a resistor material, such
type of arrester is known as a metal oxide lighting arrester.
 This arrester provides protection against all types of AC and DC over
voltages. It is mainly used for overvoltage protection at all voltage level in a
power system.

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 the zinc oxide is a semiconducting material of N-type. It is pulverized and
finely grained. More than ten doping materials are added in the form of fine
powder of insulating oxides such as bismuth, antimony trioxide, cobalt
oxide, manganese oxide, chromium oxide. The powder is treated with some
processes and the mixture is spray dried to obtain a dry powder.

 The ZnO element eliminates series sparks gaps in diverter. The voltage drop
in ZnO diverter takes place at the grain boundaries. There is a potential
barrier at the boundary of the each grain ZnO and this potential barrier
control the flow of current from one grain to the next.

 At normal voltage, the potential barrier does not allow the current to flow
through it. At over voltage the barrier collapse and sharp transition of
current from insulating to conducting state take place. The current start
flowing and the surge is diverted to ground.

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 3.2 Isolator
 An isolator, also known as a disconnector or disconnecting switch, is a
mechanical switch that's manually operated to isolate a faulty section of
a substation's circuit. This separation, called an air break, allows the
healthy section of the circuit to remain intact while the faulty section is
being repaired. Isolators are often used on both ends of a breaker for
safe replacement or repair

 Isolators are different from circuit breakers, which are on-load devices
that detect and trip when an electric fault occurs. Isolators, on the other
hand, are off-load devices that are only used when there is no load, or
zero current flowing through them. Isolators also have a locking system
or external lock to prevent accidental use, which is especially important
for high-voltage devices like transformers. The line isolator has an
earthing switch for line current discharge.

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 3.3 Circuit Breaker

 Circuit breakers in a substation are electrical switching devices that

protect and regulate electrical systems. They can be used to open and
close circuits, either manually or automatically. Circuit breakers have
several functions, including:
 Switching equipment control
○ Circuit breakers can be used to control the flow of electricity for
maintenance or repair.
○ Worker safety
○ Circuit breakers can electrically isolate circuits or units that are
being maintained, which helps keep workers safe.
 Electrical system reliability and safety
○ Circuit breakers can interrupt abnormal currents, such as short
circuits and overloads, to prevent damage and maintain the
reliability of the electrical system.

Vaccum circuit breaker SF6 circuit breaker

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 Circuit Breakers are used to open and close circuits. They can be operated
manually to perform maintenance or will automatically trip if a fault
occurs. Here Use SF6 CB for 220 KV, 66 KV. For 11 KV used vacuum
circuit breaker in this substation. A Circuit Breaker operates only when
the spring is charged. It is operated within milliseconds. In the SF6 circuit
breaker, the SF6 (sulfur hexafluoride)(at 6 bar) gas is used as an arc-
quenching medium. Similarly in the vacuum circuit breaker, the vacuum
(10-5 mmHg) is used as an arc quenching medium.

3.4 Current Transformer

 CT is a stepdown transformer (in terms of current). The protection
system is not possible without a current transformer i.e. substation
creation is not possible without CT. Converts high-value primary current
to 1A or 5A (1A in this substation) in secondary.
 Current always flows through a closed circuit. Hence the CT secondary
circuit must always be closed and cannot be kept open as the secondary
to primary balance occurs. If, by mistake, the CT secondary is open-
circuited, the secondary peak voltage may reach up to some kilovolts.
Accordingly, the working flux increases and the CT core gets saturated.
Hence the CT fires.
 A single CT has multiple cores inside it. These cores are for different
purposes such as OC protection, differential protection and metering.
 The ratio is 300-600/1-1-1A and 100-150/1-1-1A. In the 66 kV CT there
are 3 cores typically used these three are described as follows:-

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 Core-1 is used of 0.5 class. (used for metering)

 Core-2-5P10 is used in the overcurrent relay.

 Core-3 PS class used in numerical relays. (for differential protection) CTs are
marked P1 and P2.

 Normally P1 is kept beside the bus.

 In 220kV CT there are 5 cores which include the the main 3 cores of the 66 kV
CT and the other two cores are
 Core-4/5- is PS class which is used for numerical relays. (may be used for

distance protection). Is to be shorted if not used.

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 3.4.1 current transformer test
 polarity test
 ratio test
 IR test
 Knee point voltage test
 Tan-delta test
3.4.1.1 Polarity test

 The polarity test should be taken so that S1 should be found relative to P1

ie primary P1 should be concerning S1 in secondary. It is called the
polarity test. A 1.5V cell ie DC supply is required to test it. A
galvanometer that can display mA or μA. For the test Fig. indicated in As
shown, when
1.5V cell is supplied to +Ve P1, and -Ve P2, is connected to S1 and
galvanometer across S2 if the polarity is correct if the galvanometer
moves clockwise. A reading of 1.5 V is usually taken by touching the cell.
Because it contains mA current. So it gets discharged soon.

3.4.1.2 Ratio test

 Ratio of CTs used in substations.

 66kV side 300-600/1-1-1A, 100-150/1-1-1A,

 11 kV side 150-300/5 Amp, 600-900/5 Amp

 Ratio test Fig. indicated in Suppose the current injection kit should be
100Amp for the ratio test of CT used in the line. And MA must be a
measurable A meter.
 By connecting a wire across P1 and P2 of CT, 30 Amp is given between
1S1 and 1S2 i.e. 300 ratio is to be tested, if 30Amp current is given on
the primary side, 100mA current should be getting between 1S1 and
21
1S2 in the secondary. So the ratio is correct. In this way, the ratio test of
each CT

22
 can be taken.

3.4.1.3 IR test

 Megger is used to test the insulation of the CT. 5kV is applied to the test
terminals and these are used to check the resistance between the two
test terminals.
 The IR test is used to get the resistance between at 5KV potential,
P1 to core

P1 to core

At 500V

Core 1 to Core 2

Core 2 to Core 3

Core 3 to Core

1 Core 1 to

earth Core 2

to earth Core

3 to earth

This data is noted and compared with new data as this is a yearly test. And that is
called conditioning monitoring.

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 3.4.1.4 IR test

 Megger is used to test the insulation of the CT. 5kV is applied to the test
terminals and these are used to check the resistance between the two
test terminals.
 The IR test is used to get the resistance between at 5KV potential,

P1 to earth
P1 to core
2 P1 to core
3

At 500v,
Core 1 to core 2
Core 2 to core 3
Core 3 to core
1 Core 1 to
earth Core 2 to
earth Core 3 to
earth

This data is noted and compared with new data as this a yearly test. And that is
called conditioning monitoring.

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 3.4.1.5 Knee Point Voltage Test

 This test should have a point voltage test kit with a meter capable of
measuring 0 to 2kV and 0 to 100mAof current. Fig. has shown.
Accordingly this test is taken in Ps class. By connecting as shown in Fig,
first mA is measured at 100v, then mA is measured at 500v, then the CT
shown above should be given 1000v or 1400v giving 25mA or 30mA as
the case may be.

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 3.4.1.6 Tan-Delta test

 Tan delta is defined as the ratio of the resistive to capacitive

components of electrical leakage current, indicating insulation health.
In this test, the insulation paper is wrapped over the primary rod. An
ideal insulator behaves like a capacitor with no impurities, purely
allowing capacitive current flow. As many layers as there are layers are
combined and fed to the Tan-Delta cap. Capacitance is formed between
these layers. A sheet of insulation paper has a voltage of 5 kV. This test
is measured from C1 and C2, The test can be done by opening the tan-
delta cap and connecting the wires of the kit to measure the value of C1
and C2. Testing insulation with the tan delta test at low frequencies
ensures an accurate assessment of insulation health by controlling
power requirements and improving measurement precision. Tan delta
values provide insights into the insulation’s condition; stable values
across different voltages suggest good insulation while increasing

26
values indicate deterioration.

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 3.5 Potential Transformer
 A potential transformer (PT), also known as a voltage transformer (VT),
is a measuring device used in power systems to convert high voltage
values to lower ones for protection and measurement purposes. PTs are
designed to have an accurate voltage ratio and phase relationship and to
present a negligible load to the supply being measured. This allows for
accurate secondary connected metering.
 They are also used in protective relay devices and metering devices.

 PTs are electromagnetic, outdoor type, single phase, oil-filled, and self-
cooled. They have shaded porcelain bushing or insulators and are
suitable for operation without protection from sun, rain, and dust.
 The primaries of PTs are rated from 400 V to several thousand volts, and
secondaries are always for 110 V. Up to voltages of 5,000, PTs are
usually of the dry type. If the voltage is between 5,000 and 13,800 volts,
then the transformer
 may be either dry type or oil-immersed type.

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 Chapter 4 : Power Transformers

 Power transformers are electrical instruments used in transmitting

electrical power from one circuit to another without changing the
frequency. They operate by the principle of electromagnetic induction.
They are used in transmitting electrical power between generators and
distribution primary circuits.

4.1 Cooling Mechanisms

 There are usually 3 types of cooling mechanisms.

4.1.1 Oil Natural Air Natural (ONAN)

 In this type of cooling mechanism, the transformer is naturally

cooled down by the natural forces of oil and air (in the radiator)
the oil (when hot) gets less dense and travels upwards, and then
the radiators cool down the oil and make it denser means making
it heavier and this brings down the oil in the transformer core.
4.1.2 Oil Natural Air Forced (ONAF)

 In this type of cooling mechanism, the radiators are cooled by

using external 3-phase induction fans this method is known as the

forced air cooling mechanism the fans make the radiator plates
cool down faster resulting in a more efficient method of cooling
and this will make the transformer more capable of loading i.e, the
transformer can take more loads in this type of cooling
mechanism. The fan speed is also variable in some high-capacity
transformers so that

29
according to the temperature the speed of the fans will

30
 automatically adjusted.

4.1.3 Oil Forced Air Forced (OFAF)

 In this type of cooling mechanism, in addition to the forced cooling
of the transformer between the radiators and the transformer
main tank. As in this method the cooling is the most efficient
hence the highest load can be transformed by the transformer by
this method.
 The loading of the transformer also depends on the cooling
methods for example, here in the 160 MVA transformers, when
the method of cooling is ONAN the loading will be limited to 80
MVA, when the process of cooling is ONAF the loading will be
limited to 120 MVA and when the cooling is maximized the
loading limit will also be maximized i.e., 160 MVA. hence
according to the load the cooling of the transformer is
automatically done for maximum efficiency.

4.2 Transformers Details

 Here in the SANTEJ 220kV substation, there are 2 transformers

(220 kV/66kV) ., 1 transformers of 160 MVA, and 1 transformers
of 160 MVA.
 All the transformers are 3 phase 50 Hz. transformers having
connection symbol as YNyn0 some of the specifications of the 160
MVA transformer are as follows:

No load voltage HV :- 220kV Total weight :- 2,05,000

No load voltage LV :- 66kV Oil Quantity :- 60000

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Litre Line Current HV (OFAF):- 419.891A

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No Load Loss (guaranteed):-

64KW(Max.) Line Current LV (OFAF):-

1399.637A

No Load Loss (measured):-

60.42KW(Max.) Aux. Loss (guaranteed):-

11KW(Max.) Load Loss (guaranteed):-

364KW(Max.) Aux. Loss (measured):-

7.56KW(Max.) Load Loss (measured):-

354.344KW(Max.)

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4.3 Important parts of the Power Transformers

4.3.1 OLTC:- On-load tap changers (OLTCs) are a key

mechanical component in transformers that regulate voltage
and phase shifting without interrupting the load current.
OLTCs work by changing the number of turns in one of the
transformer's windings. They're fitted with tapings that can
be slid along the windings using hydraulic cylinders or electric
motors, allowing the transformer's voltage level to be
adjusted up or down to meet load requirements. Here the
OLTC has a tapping range of +15% to -5% in steps of 1.25%
each on the LV side.

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 4.3.2 Pressure Relief Valve (PRV):- A pressure relief
valve (PRV) is a safety device that protects transformers from
damage caused by high oil pressure buildup during fault
conditions. The PRV is usually mounted on top of the
transformer but can be installed in any position on the cover
or wall. When the pressure inside the transformer exceeds a
pre-set limit, the PRV opens its valve clap, which a spring
holds in place. The valve clap releases the internal pressure
until it declines. PRVs are adjustable and can be set to relieve
pressure within a specific range, making them suitable for
processes with varying pressure requirements.
 PRVs can be used in transformers, pressure tanks, and pressure
lines for both indoor and outdoor applications. They are also
suitable for repeated operation, unlike conventional explosion
vents.

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 4.3.3. Buchholz Relay:- A Buchholz relay is a safety device
that protects and monitors insulated liquid-filled transformers
with expansion tanks and earth leakage coils. It's installed in the
cooling circuit of the transformer and monitors internal gas
accumulation and oil flow. The relay responds to faults such as
gas or excessive flow of the insulating liquid with a warning or
disconnection signal. This prevents damage to the transformer
or even its destruction.
 The relay operates based on mechanical phenomena to detect
minor faults through gas accumulation or major faults indicated by
oil surges. When a serious fault occurs, the generation of gas is so
rapid that an oil surge is set up through the relay. This oil flow
impinges upon a flap fitted to the trip element, causing it to rotate
and bring the mercury switch to the closed position. This in turn
operates the tripping devices.

36
4.3.4 Breather:- A transformer breather, also known as a
dehydrating breather, is a cylindrical vessel that removes moisture
from the air that flows into a transformer's conservator tank while
the transformer is cooling down. The breather contains silica gel
beads or crystals that absorb moisture from the air, protecting the
transformer's insulating liquid and preventing condensation in the
expansion tank.

4.3.5 Nitrogen Injection Fire Prevention System:- A

Nitrogen Injection Fire Prevention System (NIFPS) is a fire safety
system that uses nitrogen gas to prevent oil tank explosions and
fires in transformers. When a transformer experiences a
temperature rise, internal faults, or arcing, the NIFPS can sense

37
the issue and activate valves to drain oil from the tank and inject
nitrogen gas to displace oxygen. The nitrogen acts as a cooling
and insulating medium, and can quickly extinguish fires. NIFPS
systems have several advantages over other fire prevention
systems, including:
 Low cost: compared to other systems, NIFPS systems are relatively
inexpensive.
 Low maintenance: NIFPS systems require minimal maintenance and
running costs.
 Unaffected by climate: NIFPS systems are not affected by changes in the
weather.

38
 Chapter 5 : Battery Room

 Every substation needs a battery room for DC supply. This DC supply is

needed for the functioning of numerical relays and also an auxiliary supply
for the annunciator. This DC supply also provides DC supply to all the
panels and PLCC systems. Generally, two types of DC supply used in 220 KV
Substation

1. 110 V

2. 48 V

 In this substation, 2 V led acid cells connect in a series combination each

cell capacity 250AH. Also, there is an auxiliary set of the same battery
backup so that it could be used in case of emergencies.
 For Battery charging use two types of chargers:

1. Float charger : During normal operation, the float charger is on and

continues to supply the DC load, and the battery is floated with it.
2. Boost Charger : If the battery is discharged and demands current over a
set limit, the boost charger is switched on. The boost charger is switched
off automatically on the battery reaches the desired level.

39
 The float charger is directly connected to the load & Boost charger is
connected directly to the battery. During normal operation, the Float
charger is on and continues to supply the DC load, and the battery is
floated with it. If the battery is discharged and demands current over a
set limit, the Boost charger is switched on. The boost charger is switched
off automatically on the battery reaches the desired level.

40
 Chapter 6 : Control room
 The Control Room contains relay panels and control panels.

 The Control and relay panels need a DC supply which is given by

Batteries which is in the battery room.
 The Control and relay panels is the most important equipment of the
substation as they work as shield guards for all substation equipments
and electrical networks. Moreover, these panels are useful to control the
flow of electricity as per the voltage class and detect the faults in the
Transmission Line.
 The Control room also contains a satellite clock and a PMU which is the
phasor measurement unit these help in determining the date and exact
time of a particular event. For instance if a sort of fault occurs the PMU
helps in time stamping the event and all the details of the event. This
helps in further stopping the occurrence of the fault and preparing for
the overloads. In case of cascade triping this helps in identifying the
actual location of the fault hence clearance becomes easier and
troubleshooting becomes more easier.

41
6.1 Types of Panels in Substation

 Line control and relay panel

 Transformer incomer panel
 Bus coupler panel
 DCDB panel
 PLCC panel

42
 6.1.1 Line control and relay panel

 The function of the control and relay panel

1. measure active power & reactive power

2. measure each phase current during normal & fault condition
3. measure total energy in units (kWh)
4. indication bulb & semaphore
5. annunciator windows & alarm
6. differential relay connect in the panel
7. control switches are placed in the panel

6.1.2 Transformer incomer panel and bus coupler panel

 The transformer incomer panel is used to measure & control incoming

power from the transformer LV side and this panel links between
transformer incoming power via UG cable and 11kv bus bar.

43
 This panel includes a circuit breaker, current transformer, relay,
ammeter, MW meter, KVAR meter, KWh meter, voltmeter, indication
LED, annunciator, alarm, and control switches.
 A bus coupler panel is used to connect two buses and it is used for
increase power reliability during maintenance and also fault conditions.
 The transformer control and relay panel are used for controlling
transformer CB manually as well as automatically by relay and
transformer protection relays are placed in this panel.
 The transformer panel indicates the type of fault that occurs in the
transformer by annunciator window and alarm.
 The remote tap changer panel's main function is to change the tap
position of the transformer and another function is to show transformer
winding and oil temperature, and control the cooling fan and oil pump.
 PLCC panel is used for communication which is the power line carrier
communication.
 DCDB panel used for DC distribution for control room Capacitor bank use for
improving power factor.

44
 Chapter 7 : Protection systems

7.1 Distance protection

 Distance protection is a power system protection method that

detects and isolates faults on transmission lines. It works by
measuring the line's impedance and comparing it to a preset
value. When a fault occurs, the line's impedance changes, which
the distance relay detects and signals to the circuit breaker to
isolate the faulty section. Distance protection also use for detect
fault distance on transmission line.

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7.2. Busbar protection

 The scheme of busbar protection, involves, Kirchhoff's current law

, which states that, total current entering an electrical node is
exactly equal to total current leaving the node.
 Essentially all the CTs used for differential busbar protection are
of same current ratio. Hence, the summation of all secondary
currents must also be equal to zero.
 the main purpose is to detect faults the bus bar zone and isolate

only the faulty section while keeping the rest of the system stable
and functional.

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6.2 Protection of transformer

 The transformer is the main part of the substation. Also, the

power transformer is costly equipment and a highly reliable
piece of equipment of the Substation. So, the protection of the
transformer is the most vital records.

 Differential protection for transformer.

 Restriction Earth fault (REF) protection.
 Overcurrent (backup) protection.
 Buchholz Relay protection.
 Thermal protection ( WTI & OTI protection ).
 Pressure Relief Valve ( PRV protection).

7.3.1 Differential Protection

 This protection scheme is one simple conceptual technique. The

differential relay compares between the primary current and secondary
current of the power transformer, if any unbalance is found between the
primary and secondary currents the relay will actuate and intertrip both
the primary and secondary circuit breaker of the transformer.

47
 Figure 8.3

7.3.2 Restricted earth fault (REF)

 In the Restricted Earth Fault scheme the common terminals of phase CTs
are connected to the secondary of Neutral CT in such a manner that the
secondary unbalance current of phase CTs, and the secondary current of
Neutral CT will oppose each other. If both currents are equal in
amplitude there will not be any resultant current circulating through the
said closed path. The Restricted Earth Fault Relay is connected in this
closed path. Hence the relay will not respond even if there is an
unbalancing in-phase current of the power transformer.
 The restricted earth-fault stage operates exclusively on earth faults
inside the area of protection. The area of protection is limited by the
phase current transformers and the current transformer of the neutral
earthing circuit.
 The earth fault relay is placed in the residual part of the current
transformers shown in the figure below. This relay protects the delta or
unearthed star winding of the power transformer against the fault
current. The connection of earth fault relay with the star or delta

48
winding

49
 of the transformer.

 Restricted Earth Fault Protection(REF) protects the zone between the

Transformer Star side winding and its Neutral Terminal which is
earthed. It senses the fault current only in this particular zone so it is
called Restricted protection.
 The earth fault current is sensed from the bushing CTs of the phases and
neutral side CT which may be either bushing CT or by the external CT in
case of resistive earthing.

50
 7.3.3 Backup protection

 Backup protection of electrical transformer is simple Over Current and

Earth Fault protection are applied against external short circuits and
excessive overloads.

Figure 8.4

7.3.4 Buchholz relay

 The Buchholz relay's purpose is to give protection to a transformer from

the different faults happening in the transformer like the Short circuit,
inter-turn, core, incipient, etc. This relay will sense these faults and shut
the Alarm circuit.

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 Whenever a small fault happens within the electrical device, heat is made by the
fault currents. The heat causes the decomposition of electrical devices oil and
gas bubbles are made. These gas bubbles run in the upward direction and are
collected .
 The insulating transformer oil will be decomposed in different hydrocarbon
gases, co2 and co.
 The lower element consists of a baffle plate and a merqury switch. This plate is
fitted on a hinge just in front of the inlet of the buchhloz relay in a transformer
in such way that when oil enters in the relay from that inlet in high pressure
the alignment of the baffle plate along with the mercury switch attached to it,
will change.
 Sometimes, oil leakage in the main tank can lead to air bubbles accumulating in
the upper part of the buchhloz container, causing the oil level to fall and
triggering the alarm circuit.

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7.3.5 Thermal Protection

7.3.5.1 Oil Temperature Trip Relay:- This relay senses oil

temperature when an internal fault like insulation

failure in one phase of winding and shorted or a local
hotspot is generated, so the produced temperature is
transferred to oil, and oil gets heated. When the oil
temperature increases and exceeds a set value, this oil
temperature relay operates.

7.3.5.2 Winding Temperature Indicator:- indicates temperature,

which is proportional to load current plus the top oil

temperature of the transformer. The indicator is
provided with two/four mercury switches. One is used
for alarm, the second is used for the trip, the third is for
fan control, and the fourth is for Pump. The
temperature settings of the switches are different from
each other for discrimination.

53
 7.3.6 Pressure Relief Valve (PRV)

 In case of a severe fault in the transformer, the internal pressure may

build up to a level, which may result in an explosion of the tank. To
avoid such a contingency a Pressure relief valve is fitted on the
transformer. Normally, the pressure relief device valve PRD will be
mounted on top of the transformer.
 If pressure arises inside a transformer and exceeds a pre-set pressure
limit, the pressure safety valve PRD opens its valve clap, which is
held by a spring and releases the internal pressure until it declines.
After a decrease in the pressure, the pressure valve clap moves back
to its original position and closes completely
 The working principle of the transformer pressure relief valve is very

simple. If pressure arises inside a transformer and exceeds a pre-set

pressure limit, the pressure safety valve opens its valve clap, which is
held by a spring and releases the internal pressure until it declines.
After the decrease of the pressure, the pressure valve clap moves
back to its original position and closes completely. Normally, the
pressure relief device will be mounted on top of the transformer. Due
to internal faults, it is suggested to have such pressure relief valves to
protect the transformer and release arising pressure quite suddenly.

54
55
 Chapter 8 : Equipment testing

 The testing of the electrical and electronic equipment of the substation is

necessary to ensure the equipment is properly working and there is no
faults. Also it helps of set an offset if something is not according to the
standards.

8.1 Lightening Arrester Testing

8.1.1 LCM testing

 A Lightning Arrester Leakage Current Measurement (LCM) test measures

the leakage current flowing through a Lightning/Surge Arrester (LA)

and counts the number of surges it has experienced. The leakage current
is measured in the LA by observing the meter provided on the LA which
has the scales of red, green, and yellow color. This meter shows the
leakage current of the LA it also have the counter scale on it so the
Leakage current could be measured.

8.2. Circuit Breaker Testing

8.2.1. Insulation Resistance Test (IR) test

 Resistance testing is crucial for verifying that the insulating material that
makes up the molded case breakers are performing correctly. To test for
insulation resistance, an instrument known as a “megger” is used. A
megger instrument applies a known DC voltage to a given wire for a
given
56
 period to test the resistance within the insulation on that particular wire
or winding. Voltage must be applied because resistance tested with an
ohm meter may vary when there are no potential differences present. It
should also be noted that if you apply a voltage that is too high for that
insulation to withstand, then you could potentially damage the
insulation. Meggers are rated and have specific settings that range from
300, 600, 1000, and 3000 Volt settings

8.2.2 Dynamic Contact Resistance Measurement

 Dynamic Contact Resistance Measurement (DCRM) is a test that assesses

the condition of high-voltage circuit breaker (CB) contacts. It's
considered the most comprehensive test for CBs and can help identify
abnormal wear and tear, pitting, mechanical weaknesses, or
deterioration of the operating mechanism.
 To perform a DCRM test, a 100A DC current is injected through the CB's
contacts while it's operating in close-open (C-O) mode. The voltage drop
and current are measured at a high speed, usually 10kHz or more. A
travel transducer is also used to capture the CB's travel characteristics.
The results are then plotted as a graph of resistance across the CB
contacts over time. This graph can be analyzed to identify parameters
such as contact gap, total insertion, arcing tip insertion, and main and
arcing contact resistance.

57
8.3. Battery testing
8.3.1 Voltagetest

 Voltage test is a periodic test through which batterys voltage is

determined a multimeter is used to determine the voltage of the
batteries each 2V battery should show a voltage of 2 volts in the
multimeter reading when the battery is fully charged.

8.3.2 Gravity test

 The lead-acid battery used in today's automobile is made of plates, lead,

and lead oxide in an electrolyte solution. This solution consists of 65%
water and 35% sulfuric acid. This solution's specific gravity or weight
increases as the battery charges and decreases as the battery discharges.
As the battery discharges, sulfur moves away from the solution and
toward the plates.
 The sulfur returns to the electrolyte solution. The specific gravity of the
electrolyte depends on this 65% to 35% ratio for the necessary chemical
reaction to occur. This ratio is affected by the amount of sulfuric acid
and the temperature of the solution. As the temperature drops, the
electrolyte contracts, increasing the specific gravity. As the temperature
increases, the electrolyte expands, deviating from its optimal ratio and
affecting the specific gravity reading.
 A battery's specific gravity is a great way of measuring a battery's
state of charge. This is because, during discharge, the specific gravity
decreases linearly with ampere-hours discharged. The specific

58
gravity

59
 also increases as the battery is recharged.
 A hydrometer measures the specific gravity of the electrolyte solution in
each cell. It's a tool used to measure the density or weight of a liquid
compared to the density of an equal amount of water.

8.4 Transformer testing

8.4.1 Open CircuitTest

 The open-circuit test, or no-load test, is one of the methods used in

electrical engineering to determine the no-load impedance in the
excitation branch of a transformer. The no load is represented by
the open circuit, which is represented on the right side of the
figure as the "hole" or incomplete part of the circuit.

8.4.2 Short CircuitTest

 A short circuit test is conducted on a transformer to determine

copper loss. This test is conducted on the HV side keeping the LV
side short circuit. This test is performed at the rated current.
Since, the LV is short circuited, so the power factor will be high or
unity in nature.

8.4.3 Turns Ratio Test

 The TTR test compares the ratio of the transformer's

nominal voltage and frequency on the high voltage
(HV) side to the measured no-load voltage on the low
voltage (LV) side. The results are then compared to the
nameplate ratings to check for
60
 issues such as insulation deterioration, shorted turns,
core heating, or other abnormalities. The test ensures
the correct ratio of primary and secondary turns, which
is important for improving power quality and system
stability and safety, as well as controlling production
process errors and revealing assembly problems.

8.4.4 IR Test

 Transformer insulation resistance measurement is an important

task that needs to be performed periodically to ensure the safety
and reliability of the transformer.
 The insulation resistance of the transformer indicates the
quality of insulation material used and signifies the level of
effectiveness of the insulating system surrounding the winding.
In this article, we will discuss the methods used to measure the
insulation resistance of a transformer.
 The most common method used to measure the insulation
resistance of a transformer is the Megger test. By using a Megger,
we can measure the insulation resistance of the transformer by
creating a high voltage, low current DC charge across the
insulation material of the transformer. This causes a small current
to be drawn and the measurement of the resistance is then taken.
 The results of the Megger test are usually expressed in megohms
(MΩ). The acceptable insulation resistance values for
transformers vary based on the voltage rating of the transformer.
A rule of thumb is that the insulation resistance should be at

61
least 100 times the

62
 operating voltage.

8.4.5 Magnetic Balance Test

 The magnetic balance test is a most commonly used proactive test

is performed only on three-phase transformers to detect the
faults in the core and to verify the imbalance in the magnetic
circuit also to identify inter-turn faults in the transformer at the
early stage of manufacturing work.

8.4.6 Vector Group Test

 The vector group test of a transformer checks the phase sequence

and angular difference to ensure transformers can operate in
parallel. Matching the phase sequence is essential for parallel
operation of transformers to avoid short circuits.

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 8.4.7 SCADA SYSTEM

 SCADA (Supervisory Control and Data Acquisition) is a computer-

based system used for remote monitoring and control of
industrial processes. It plays a vital role in substations, power
plants, water treatment facilities, and manufacturing industries. A
typical SCADA system consists of several key components: the
Human-Machine Interface (HMI) provides operators with real-
time graphical displays and control options; Remote Terminal
Units (RTUs) and Programmable Logic Controllers (PLCs) collect
data from field sensors and execute control commands; a secure
communication network links these field devices to the central
control center; and the SCADA master station or server manages
data storage, visualization, and supervisory control. SCADA
systems work by continuously gathering data from sensors,
transmitting it over communication networks to the control room,
and allowing operators to monitor system status and issue control
commands remotely. This enables quick fault detection, improved
operational efficiency, centralized control, and enhanced safety.
By automating data collection and control, SCADA systems reduce
manpower needs and ensure reliable, efficient operation of
complex industrial and electrical systems.

64
 Chapter 9 : Maintenance and LCP
 Substation Maintenance is a process of periodic, planned
inspection of and, if necessary, repair, and replacement of all
switchgear and ancillary equipment in the substation. If 220 KV
Substation Maintenance is required, then 48 hours ago inform the
state load dispatch center ( SLDC). If SLDC allows the maintenance
will occur at a particular date and time limit.
 The LCP(Line clearance Permit) system is used for safety
purposes. LCP is one type of permission to do maintenance in the
substation which is given by the service operator to the
maintenance operator. In LCP also mentioned that which switch
yard or bays parts maintenance occurs. When all work is done the
LCP is returned to the substation on service operator.
 Cleaning and oiling of contacts of an isolator switch in the yard for
PMM work in 220 KV Substation. Cleaning the insulator in the
yard and tightening the jumper and its jo-contacts. If the JO
contacts heated then replace it and put new contacts. Cleaning the
breakers, and their wiring and cleaning the panels of the control
room. Check the 11 KV Bus Bar and the cable box and check the
cable insulation and bus nut bolt. To remove a hot point by
checking the previous hot point. Whenever doing maintenance the
earthing is compulsory. Check the all relays of the transformer
and lines.

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 Chapter 10 : Conclusion

In conclusion, my internship at GETCO has been a valuable and

enlightening experience. Over the course of my time with the
organization, I have the opportunity to gain hands-on experience in the
dynamic field of electrical engineering. I become familiar with the layout
of the sub-station and the functions of critical components such as
transformer, circuit breakers, and protective relays. Working alongside
dedicated professionals, I have contributed to critical projects related to
substation operations. I worked closely with experienced engineers and
technicians, learning the importance of teamwork and effective
communication in achieving operational excellence. Moreover, I have
developed a deep appreciation for the intricate workings of the electrical
grid and its importance in ensuring a reliable and efficient supply of
electricity to communities. I was involved in diagnosing and resolving
technical problems, which honed my analytical and problem-solving
skills.

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