This document is an industrial training report submitted by Swapnil Kumar Gupta for their Bachelor of Technology degree in Electrical Engineering. The report provides an overview of Swapnil's 2-week industrial training at the 220kV substation in Rewa Road, Allahabad, which is operated by Uttar Pradesh Power Transmission Corporation Limited. The report includes details about the equipment and processes at the substation, as well as declarations, acknowledgements, and chapters covering topics like the selection of substation sites, common equipment used in 220kV substations, and descriptions of the transformer and other components.

1. INDUSTRIAL TRAINING
REPORT ON
UTTAR PRADESH POWER TRANSMISSION CORPORATION LIMITED
220KV SUBSTATION REWA ROAD
ALLAHABAD
Submitted
In Partial Fulfillment of the Requirements
For the Award Degree of
Bachelor of Technology
In
ELECTRICAL ENGINEERING
Submitted by
Swapnil Kumar Gupta
(1601020056)
SUBMITTED TO: -
Department Of Electrical Engineering
UNITED COLLEGE OF ENGINEERING AND RESEARCH
(A-31, UPSIDC Industrial Area, Naini, Allahabad U.P. – 211008)
Dr. A.P.J. Abdul Kalama Technical University
(Lucknow, Uttar Pradesh 226021)

2. DECLARATION
I, Swapnil Kumar Gupta, Roll No 1601020056, Class B. Tech. (Electrical
Engineering) 2016-2020 of the United College of Engineering and Research,
Allahabad hereby declare that the Industrial Training report entitled 220KV
TRANSMISSION SUBSTATION is an Original work and same has not been
submitted to any other institute for the award of any other degree.
Signature of the Candidate
Countersigned (Head of the Department)

3. ACKNOWLEDGEMENT
“Gratitude is not a thing of expression; it is more than a matter of feeling.”
I would like to express my deep gratitude to Mr. Vikram Singh Yadav, Executive Engineer,
and Mr. Ram Awadh Yadav, Assistant Engineer at 220KV Substation Allahabad for their
active support and continuous guidance without which it would have been difficult of me to
complete this project. They were generous enough to take their time out of their regular work
to lend a helpful hand whenever I needed one and enabling me to complete this project.
I would also like to mention the generous guidance of Mr. Nouman Ahmad,
Superintendent Engineer and Mr. Vickram Singh Yadav, Assistant Engineer (A.E.)
together with my internal project guide Er. S. K. Gupta whose guidance helped me settle
down in the organization and successfully complete the project within the relatively short
time frame of 2 weeks, from 10th January, 2018 to 23nd January, 2018. They were
supporting enough to give me an opportunity to be a part of such a prestigious organization
for 2 weeks and learn the day to day functioning.
Last but by no means the least, I’m grateful to the Training and Placement Cell of my
institute, headed by Ms. Divya Ma’am for providing a quick turnaround time for all the
requests.
I also wish my deep sense of gratitude to Mr. Swapnil Srivastava (H.O.D.: EE
Department) and other faculty members whose guidance and encouragement made my visit
successful.
SWAPNIL KUMAR GUPTA

4. UTTAR PRADESH POWER CORPORATION LIMITED
 Uttar Pradesh Power Corporation Limited (UPPCL) is the company responsible
for Electricity transmission and distribution within Uttar Pradesh.
Its chairman is Shri Alok Kumar Singh.
Uttar Pradesh Power Corporation Limited (UPPCL) procures power from; state
government owned power generators, central government owned power generators
and Independent Power Producers through power purchase agreement for lowest per
unit cost of electricity.
 The creation of Uttar Pradesh Power Corporation Ltd. (UPPCL) on January 14, 2000
is the result of power sector reforms and restructuring in UP (India) which is the focal
point of the Power Sector, responsible for planning and managing the sector through
its transmission, distribution and supply of electricity.
 UPPCL will be professionally managed utility supplying reliable and cost efficient
electricity to every citizen of the state through highly motivated employees and state
of art technologies, providing an economic return to our owners and maintaining
leadership in the country.
The causes of such a poor financial conditions of UPPCL include:-
 Higher line losses due to aging over stressed infrastructure
 Pilferage of power at large scale
 Inferior quality of transformers and other equipments
 Selling power much below its purchasing cost.
These can be overcome by forward looking, reliable, safe and trustworthy organization,
sensitive to our customers interests, profitable and sustainable in the long run, providing
uninterrupted supply of quality power, with transparency and integrity in operation.

5. ABSTRACT
 The report gives an overview of 220KV Power Substation. It includes electricity
transmission and distribution processes at UPPCL, Rewa Road, Allahabad substation.
 Its substation, an assembly of apparatus which is installed to control transmission and
distribution of electric power.
 Its two main divisions are: - outdoor and indoor substation.
 Different equipments used in substations are:-
Bus-bar,
Surge arrestor
Isolator
Earth switches
Current Transformers, etc.
 Transformer which is being used here is core and shell type transformer for stepping
up and down purposes.
 Different Instruments transformers, Voltage, Current and CV Transformers are also
being used.
 Finally the CVT rating which gives a total output overview.

6. TABLE OF CONTENTS
CH.NO. TOPIC NAME
1. INTRODUCTION
2. ABOUT SUBSTATION
Definition
Sub-Station
Types of Substation
220/132 KV sub-station
About the substation
3. SELECTION OF SITE
4. EQUIPMENT IN A 220KV SUB-STATION
Bus-bar
Insulators
Isolating Switches
Circuit breaker
Protective relay
Instrument Transformer
Current Transformer
Voltage Transformer
Capacitor Voltage Transformer
Metering and Indicating Instrument
Miscellaneous equipment
Transformer
Lightening arrestors
Line isolator
Wave trap
5. SINGLE LINE DIAGRAM
6. TRANSFORMER
7. INSULATOR
8. CIRCUIT BREAKER & ISOLATOR
9. CONTROL AND RELAY ROOM
10. WAVE TRAP
11. CONCLUSION

7. CHAPTER-1
INTRODUCTION
The present day electrical power system is A.C. i.e. electric power is generated, transmitted
and distributed in the form of Alternating current. The electric power is produce at the power
station, which are located at favorable places, generally quite away from the consumers. It is
delivered to the consumer through a large network of transmission and distribution. At many
place in the line of power system, it may be desirable and necessary to change some
characteristic (e.g. Voltage, AC to DC, frequency, 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 220KV to 132KV)
for transmission of electric power.
Similarly near the consumer’s localities, the voltage may have to be stepped down to
utilization level. This job is again accomplished by suitable apparatus called sub-station.

8. CHAPTER-2
ABOUT THE SUBSTATION
1. Definition of sub-station:
“The assembly of apparatus used to change some characteristics (e.g. Voltage AC to DC Freq. P.F. etc) of
Electric supply is called sub-station”
2. Sub-Station:
1. A substation is a part of an electrical generation, transmission, and distribution system.
2. Substations transform voltage from high to low, or the reverse, or perform any of several other
important functions. Between the generating station and consumer, electric power may flow through
several substations at different voltage levels.
3. Substations may be owned and operated by an electrical utility, or may be owned by a large
Industrial or commercial customer. Generally substations are unattended, relying on SCADA for
remote supervision and control.
4. A substation may include transformers to change voltage levels between high transmissions Voltages
and lower distribution voltages, or at the interconnection of two different transmission voltages. The
word substation comes from the days before the distribution system became a grid.
5. A central generation stations became larger, smaller generating plants were converted to distribution
stations, receiving their energy supply from a larger plant instead of using their own generators. The
first substations were connected to only one power station, where the generators were housed, and
were subsidiaries of that power station.
3. Types of Substation:
Substations may be described by their voltage class, their applications within the power system, the method
used to insulate most connections, and by the style and materials of the structures used. These categories are
not disjointed; to solve a particular problem, a transmission substation may include significant distribution
functions, for example.
Transmission substation
Distribution substation
Collector substation
Converter substation
Switching station
Transmission substation:
A transmission substation connects two or more transmission lines. The simplest case is where all
transmission lines have the same voltage. In such cases, substation contains high-voltage switches that allow
lines to be connected or isolated for fault clearance or maintenance. A transmission station may have
transformers to convert between two transmission voltages, voltage control/power factor correction devices
such as capacitors, reactors or static VAR compensators and equipment such as phase shifting transformers
to control power flow between two adjacent power systems.

9. Transmission substations can range from simple to complex. A small "switching station" may be little more
than a bus plus some circuit breakers. The largest transmission substations can cover a large area (several
acres/hectares) with multiple voltage levels, many circuit breakers and a large amount of protection and
control equipment (voltage and current transformers, relays and SCADA systems). Modern substations may
be implemented using international standards such as IEC Standard 61850.
Distribution substation:
It is uneconomical to directly connect electricity consumers to the main transmission Network, unless they
use large amounts of power, so the distribution station reduces voltage to a Level suitable for local
distribution. The input for a distribution substation is typically at least two transmission o r sub transmission
Lines. Input voltage may be, for example, 115 KV, or whatever is common in the area. The outputs are a
number of feeders. Distribution voltages are typically medium voltage, between 2.4 KV and 33 KV
depending on the size of the area served and the practices of the local utility. The feeders Run along streets
overhead (or underground, in some cases) and power the distribution, Transformers at or near the customer
premises. In addition to transforming voltage, distribution substations also isolate faults in either the
Transmission or distribution systems. Distribution substations are typically the points of voltage Regulation,
although on long distribution circuits (of several miles/kilometers), voltage regulation Equipment may also
be installed along the line. The downtown areas of large cities feature complicated distribution substations,
with high voltage switching, and switching and backup systems on the low-voltage side. More typical
Distribution substations have a switch, one transformer, and minimal facilities on the low-voltage side.
Collector substation:
In distributed generation projects, a collector substation may be required. It resembles a distribution
substation although power flow is in the opposite direction. The collector substation can also provide power
factor correction if it is needed and metering. In some special cases a collector substation can also contain an
HV DC converter station. Collector substations also exist where multiple thermal or hydroelectric power
plants of Comparable output power is in proximity.
If no transformers are required for increase of voltage to transmission level, the Substation is a switching
station.
Converter substation:
Converter substations may be associated with HV DC converter plants, traction current, or interconnected
non-synchronous networks. These stations contain power electronic devices to Change the frequency of
current, or else convert from alternating to direct current or the reverse. Formerly rotary converters changed
frequency to interconnect two systems.
Switching station:
(Switchyard at Rewa Road, Allahabad, 2018)

10. A switching station is a substation without transformers and operating only at a single voltage Level.
Switching stations are sometimes used as collector and distribution stations. Sometimes they are used for
switching the current to back-up lines or for parallelizing circuits in case of Failure.
A switching station may also be known as a switchyard, and these are commonly located directly Adjacent
to or nearby a power station. In this case the generators from the power station supply their power into the
yard onto the Generator Bus on one side of the yard, and the transmission Lines take their power from a
Feeder Bus on the other side of the yard.
An important function performed by a substation is switching, which is the connecting and Disconnecting of
transmission lines or other components to and from the system. Switching Events may be "planned" or
"unplanned".
A transmission line or other component may need to be De-energized for maintenance or for new
construction, for example, adding or removing a Transmission line or a transformer.
To maintain reliability of supply, no company ever brings down its whole system for maintenance. All work
to be performed, from routine testing to Adding entirely new substations, must be done while keeping the
whole system running.
Perhaps more important, a fault may develop in a transmission line or any other component.
Some examples of this:
A line is hit by lightning and develops an arc
A tower is blown down by high wind.
The function of the switching station is to isolate the faulted portion of the system in the shortest possible
time. De-energizing faulted equipment protects it from further damage, and isolating a Fault helps keep the
rest of the electrical grid operating with stability.
 220KV Sub-station:
220KV Sub-Station forms an important link between Transmission network and Distribution Network.
It has a vital influence of reliability of service. Apart from ensuring efficient Transmission and Distribution
of power, the sub-station configuration should be such that it enables easy maintenance of equipment and
minimum interruptions in power supply. A Sub-Station Is constructed near as possible to the load center.
The voltage level of power transmission is decided on the quantum of power to be transmitted to the load
center.
4. About the substation:
The most important of any substation is the grounding (Earthing System) of the instruments, transformers
etc. used in the substation for the safety of the operation personnel as well as for proper system operation
and performance of the protective devices. An earths system comprising of an Earthing Mat buried at a
suitable depth below ground and supplemented with ground rod sat suitable points is provided in the
substations. These ground the extra high voltage to the ground as it is dangerous to us to go near the
instrument without proper earth. If the instruments are not ground properly they may give a huge shock to
anyone who would stay near it and also it is dangerous for the costly instrument as they may get damaged by
this high voltage.

11. CHAPTER-3
SELECTION OF SITE
Main points to be considered while selecting the site for Grid Sub-Station are as follows:
1. The site chosen should be as near to the load center as possible.
2. It should be easily approachable by road or rail for transportation of equipments.
3. Land should be fairly leveled to minimize development cost.
4. Source of water should be as near to the site as possible. This is because water is required for various
construction activities (especially civil works), Earthing and for drinking purposes etc.
5. The sub-station site should be as near to the town / city but should be clear of Public places,
aerodromes, and Military / police installations.
6. The land should be have sufficient ground area to accommodate substation Equipments, building,
staff quarters, space for storage of material, such as store Yards and store sheds etc. with roads and
space for future expansion.
7. Set back distances from various roads such as National Highways, State Highways should be
observed as per the regulations in force.
8. While selecting the land for the Substation preference to be given to the Govt. Land over private
land.
9. The land should not have water logging problem.
10. Far away from obstructions, to permit easy and safe approach/termination of high Voltage overhead
transmission lines.

12. CHAPTER-4
EQUIPMENT IN A 220KV SUB-STATION
The equipment required for a transformer Sub-Station depends upon the type of Sub-Station,
Service requirement and the degree of protection desired.
220KV EHV Sub-Station has the following major equipments:
Bus-bar
Insulators
Isolating Switches
Circuit breaker
Protective relay
Instrument Transformer
Current Transformer
Voltage Transformer
Metering and Indicating Instrument
Miscellaneous equipment
Transformer
Lightening arrestors
Line isolator
Wave trap
BUS-BAR:
When a no. of lines operating at the same voltage have to be directly connected electrically, busbar are used,
it is made up of copper or aluminum bars (generally of rectangular X-Section) and operate at constant
voltage.
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.
.
INSULATORS:
The insulator serves two purpose, they support the conductor (or bus bar) and confine the current to the
conductor. The most commonly used material for the manufactures of insulators is porcelain. There are
several type of insulator (i.e. pine type, suspension type etc.) and there used in Sub-Station will depend upon
the service requirement.

13. Isolating Switches:
In Sub-Station, it is often desired to disconnect a part of the system for general maintenance and repairs.
This is accomplished by an isolating switch or isolator.
An isolator is essentially a knife Switch and is design to often open a circuit under no load, in other words,
isolator Switches are operate only when the line is which they are connected carry no load. For example,
consider that the isolator are connected on both side of a circuit breaker, if the isolators are to be opened, the
C.B. must be opened first.
Circuit breaker:
A circuit breaker is an equipment, which can open or close a circuit under normal as well as fault condition.
These circuit breaker breaks for a fault which can damage other instrument in the station.
It is so designed that it can be operated manually (or by remote control) under normal conditions and
automatically under fault condition.
There are mainly two types of circuit breakers used for any substations. They are
(a) SF6 circuit breakers
(b)Spring circuit breakers
For the latter operation a relay which is used with a C.B. generally bulk oil C.B. are used for voltage up to
66 KV while for high voltage low oil & SF6 C.B. are used. For still higher voltage, air blast vacuum or SF6
cut breaker are used.
The use of SF6 circuit breaker is mainly in the substations which are having high input KV input, say above
220KV and more. The gas is put inside the circuit breaker by force i.e. under high pressure.
When if the gas gets decreases there is a motor connected to the circuit breaker. The motor starts operating if
the gas went lower than 20.8 bar. There is a meter connected to the breaker so that it can be manually seen if
the gas goes low. The circuit breaker uses the SF6 gas to reduce the torque produce in it due to any fault in
the line. The circuit breaker has a direct link with the instruments in the station, when any fault occur alarm
bell rings.
Protective relay:
A protective relay is a device that detects the fault and initiates the operation of the C.B. to isolate the
defective element from the rest of the system”. The relay detects the abnormal condition in the electrical
circuit by constantly measuring the electrical quantities, which are different under normal and fault
condition. The electrical quantities which may change under fault condition are voltage, current, frequency
and phase angle. Having detect the fault, the relay operate to close the trip circuit of CB.
Instrument Transformer:
The line in Sub-station operates at high voltage and carries current of thousands of amperes. The measuring
instrument and protective devices are designed for low voltage (generally 110V) and current (about 5A).
Therefore, they will not work satisfactory if mounted directly on the power lines. This difficulty is overcome
by installing Instrument transformer, on the power lines.

14. There are two types of instrument transformer-
1. Current Transformer:
A current transformer is essentially a step-down transformer which steps-down the current in a known ratio,
the primary of this transformer consist of one or more turn of thick wire connected in series with the line, the
secondary consist of thick wire connected in series with line having large number of turn of fine wire and
provides for measuring instrument, and relay a current which is a constant faction of the current in the line.
Current transformers are basically used to take the readings of the currents entering the substation. This
transformer steps down the current from 800 amps to 1amp. This is done because we have no instrument for
measuring of such a large current.
The main use of his transformer is:
(a) Distance Protection
(b) Backup Protection
(c) Measurement
2. Potential Transformer:
It is essentially a step – down transformer and step down the voltage in known ratio. The primary of these
transformer consist of a large number of turn of fine wire connected across the line. The secondary way
consist of a few turns and provides for measuring instruments and relay a voltage which is known fraction of
the line voltage.
3. C V T:
A capacitor voltage transformer (CVT ) is a transformer used in power systems to step-down extra high
voltage signals and provide low voltage signals either for measurement or to operate a protective relay. In its
most basic form the device consists of three parts: two capacitors across which the voltage signal is split, an
inductive element used to tune the device to the supply frequency and a transformer used to isolate and
further step-down the voltage for the instrumentation or protective relay.
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 kilovolts 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.

Metering and Indicating Instrument:
There are several metering and indicating Instrument (e.g. Ammeters, Volt-meters, energy meter etc.)
installed in a Substation to maintain which over the circuit quantities. The instrument transformers are
invariably used with them for satisfactory operation.
Miscellaneous equipment:

15. In addition to above, there may be following equipment in a Substation:
i) Fuses
ii) Carrier-current equipment
iii) Sub-Station auxiliary supplies
Transformer:
There are four transformers in the incoming feeders so that the four lines are step down at the same time. In
case of a 220KV or more KV line station auto transformers are used. While in case of lower KV line such as
less than 132KV line double winding transformers are used Auto transformer.
Transformer is static equipment which converts electrical energy from one voltage to another. As the system
voltage goes up, the techniques to be used for the Design, Construction, Installation,
Operation and Maintenance also become more and more critical. If proper care is exercised in the
installation, maintenance and condition monitoring of the transformer, it can give the user trouble free
service throughout the expected life of equipment which of the order of 25-35 years.
Hence, it is very essential that the personnel associated with the installation, operation or maintenance of the
transformer is through with the instructions provided by the manufacture diverted around the protected
insulation in most cases to earth.
Auto transformer:
Transformer is static equipment which converts electrical energy from one voltage to another. As the system
voltage goes up, the techniques to be used for the Design, Construction, Installation,
Operation and Maintenance also become more and more critical. If proper care is exercised in the
installation, maintenance and condition monitoring of the transformer, it can give the user trouble free
service throughout the expected life of equipment which of the order of 25-35 years.
Hence, it is very essential that the personnel associated with the installation operation or maintenance of the
transformer is through with the instructions provided by the manufacture.
Basic principles:
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.
It is a device that transfers electrical energy from one circuit to another through inductively coupled
conductors- the transformer's coils. Except for air-core transformers, the conductors are commonly wound
around a single iron-rich core, or around separate but magnetically - coupled cores. A varying current in the
first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This
varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary"
winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical
energy will flow from the primary circuit through the transformer to the load. In an ideal transformer, the
induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by
the ratio of the number of turns in the secondary to the number of turns in the primary as follows:

16. By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage
to be "stepped up" by making NS greater than NP, or "stepped down" by making N(s) less than N(p).
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 designs is 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. Pole -mounted single-
phase transformer with center-tapped secondary. Note use of the grounded conductor as one leg of the
primary feeder.
Lightening Arrester:
Fig: 132 KV Lightening Arrester at Rewa Road, Allahabad Sub-Station
It is used to discharge the switching and lightening voltage surges to earth.
Wave trap:
Wave trap is an instrument using for tripping of the wave. The function of this trap is that it traps the
unwanted waves. Its function is of trapping wave. 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 here in the
substation.

17. CHAPTER-5
SINGLE LINE DIAGRAM (SLD)
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 these feeders enter the station they are to pass through various instruments. The instruments have their
usual functioning.
They are as follows in the single line diagram:
Lightening arrestors
C V T
Wave trap
Isolators with earth switch
Circuit breaker
BUS
Potential transformer with a bus isolator
Isolator
Current transformer
A capacitor bank attached to the bus

18. The line diagram of the substation:
Fig: Single Line Diagram of 220 KV Substation Rewa Road, Allahabad
This substation has the capacity of 220KV and can step down to 132KV using
Four input lines through the incoming feeders.
The input feeders are namely,
o PGCIL II
o PGCIL I
o OBRA III
o OBRA I
o MIRZAPUR
o ISOLUX CKT 1
o ISLOUX CKT 2
These feeders come into the substation with 220KV.
The substation of 220KV/132KV has seven outgoing feeders, namely:
 ALLAHABAD I
 ALLAHABAD II

19.  GIS
 SARAI AKIL
 SGH
 KORAV II
These out going feeders are of 132KV line.
Further, the substation of 132KV/33kKVhas ten outgoing feeders, namely: -
 REWA ROAD
 INDALPUR
 NAINI STORE
 NAINI JAIL
 KARELABAGH
 SGH
 NB II
 JP CEMENT
 ISOLUX
 NB I
 PGCIL

20. CHAPTER-6
TRANSFORMER
Transformer is a static machine, which transform the potential of alternating current at same frequency. It
means the transformer transforms the low voltage into high voltage and high voltage into low voltage at
same frequency. It works on the principle of static induction principle. When the energy transformed into
higher voltage, the transformer is called step up transformer but in case of other is known as step down
transformer.
Fig: 220/132 KV 160 MVA Transformer at Rewa Road, Allahabad Sub-Station
TYPES OF TRANSFORMER:
Power Transformer
Instrument Transformer
Auto Transformer
Further, Transformer classified in two types:
On the basis of working
On the basis of structure

21. POWER TRANSFORMER:
Fig: 132/33 KV 40 MVA transformer at Rewa Road, Allahabad sub-station
INSTRUMENT TRANSFORMER:
Fig: Instrument Transformer at Rewa Road, Allahabad Sub-Station


22. Auto Transformer:
POWER TRANSFORMER:
 Single phase transformer
 Three phase transformer
INSTRUMENT TRANSFORMER:
 Current transformer
 Potential transformer
AUTO TRANSFORMER:
 Single phase transformer
 Three phase transformer
On the basis of working:
 Step down: convert HIGH VOLTAGE into LOW VOLTAGE
 Step up: convert LOW VOLTAGE into HIGH VOLTAGE
On the basis of structure:
 Core Type
 Shell Type

23. CHAPTER-7
INSULATORS
An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it
nearly impossible to conduct an electric current under the influence of an electric field. This contrasts with
other materials, semiconductors and conductors, which conduct electric current more easily. The property
that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or
conductors.
A perfect insulator does not exist, because even insulators contain small numbers of mobile charges (charge
carriers) which can carry current. In addition, all insulators become electrically conductive when a
sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known
as the breakdown voltage of an insulator.
Some materials such as glass, paper and Teflon, which have high resistivity, are very good electrical
insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good
enough to prevent significant current from flowing at normally used voltages, and thus are employed as
insulation for electrical wiring and cables. Examples include rubber-like polymers and most plastics.
Insulators are used in electrical equipment to support and separate electrical conductors without allowing
current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment
is called insulation. The term insulator is also used more specifically to refer to insulating supports used to
attach electric power distribution or transmission lines to utility poles and transmission towers. They support
the weight of the suspended wires without allowing the current to flow through the tower to ground.
INSULATING MATERIAL
The main cause of failure of overhead line insulator, is the flash over, occurs in between line and earth
during abnormal over voltage in the system.
During the flash over, the huge heat produced by arching, causes puncher in insulator body.
PROPERTIES OF INSULATING MATERIAL:
For successful utilization, this material should have some specific properties as listed below:

24. It must be mechanically strong enough to carry tension and weight of conductors.
It must have very high dielectric strength to withstand the voltage stresses in High Voltage
system.
It must possessed high Insulation Resistance to prevent leakage current to the earth.
The insulating material must be free from unwanted impurities.
It should not be porous.
There must not be any entrance on the surface of electrical insulator so that the moisture or gases
can enter in it.
There physical as well as electrical properties must be less affected by changing temperature.
TYPES OF INSULATING MATERIALS:
Two types of insulating material are mainly used:
a. Porcelain insulator
b. Glass insulator
i) Porcelain insulator:
Porcelain in most commonly used material for over head insulator in present days. The porcelain is
aluminum silicate. The aluminum silicate is mixed with plastic kaolin, feldspar and quartz to obtain final
hard and glazed porcelain insulator material.
The surface of the insulator should be glazed enough so that water should not be traced on it.
Fig: porcelain insulator
ii) Glass insulator:
Now-a-days, glass insulator has become popular in transmission and distribution system. Annealed tough
glass is used for insulating purpose.
Fig; glass insulator
Advantages of Glass Insulator:
It has very high dielectric strength compared to porcelain.

25. Its resistivity is also very high.
It has low coefficient of thermal expansion.
It has higher tensile strength compared to porcelain insulator.
As it is transparent in nature this not heated up in sunlight as porcelain.
The impurities and air bubble can be easily detected inside the glass insulator body because of
its transparency.
Glass has very long service life as because mechanical and electrical properties of glass do not
be affected by ageing.
After all, glass is cheaper than porcelain.
Disadvantages of Glass Insulator:
Moisture can easily condensed on glass surface and hence air dust will be deposited o the wed glass
surface which will provide path to the leakage current of the system.
For higher voltage glass can’t be cast in irregular shapes since due to irregular cooling internal cooling
internal strains are caused.
TYPES OF INSULATORS:
There are five types of insulators:
1. Pin type insulator
2. Suspension type insulator
3. Strain type insulator
4. Shackle type insulator
5. Stay type insulator
1. PIN TYPE INSULATOR:
Pin Insulator is earliest developed overhead insulator, but still popularly used in power network up to 33 KV
system. Pin type insulator can be one part, two parts or three parts type, depending upon application voltage.
In 11 KV system we generally use one part type insulator where whole pin insulator is one piece of properly
shaped porcelain or glass. As the leakage path of insulator is through its surface, it is desirable to increase
the vertical length of the insulator surface area for lengthening leakage path.
Fig: pin type insulator
2. SUSPENSION TYPE INSULATOR:

26. In higher voltage, beyond 33KV, it becomes uneconomical to use pin insulator because size, weight of the
insulator become more. Handling and replacing bigger size single unit insulator are quite difficult task. For
overcoming these difficulties, suspension insulator was developed.
In suspension insulator numbers of insulators are connected in series to form a string and the line conductor
is carried by the bottom most insulator. Each insulator of a suspension string is called disc insulator because
of their disc like shape.
FIG: SUSPENSION TYPE INSULATOR
3. STRAIN TYPE INSULATOR:
When suspension string is used to sustain extraordinary tensile load of conductor it is referred as string
insulator. When there is a dead end or there is a sharp corner in transmission line, the line has to sustain a
great tensile load of conductor or strain. A strain insulator must have considerable mechanical strength as
well as the necessary electrical insulating properties.
FIG: STRAIN TYPE INSULATOR
4. SHACKLE TYPE INSULATOR:
The shackle insulator or spool insulator is usually used in low voltage distribution network. It can be used
both in horizontal and vertical position. The use of such insulator has decreased recently after increasing the
using of underground cable for distribution purpose. The tapered hole of the spool insulator distributes the
load more evenly and minimizes the possibility of breakage when heavily loaded. The conductor in the
groove of shackle insulator is fixed with the help of soft binding wire.
FIG: SHACKLE TYPE INSULATOR

27. 5. STAY TYPE INSULATOR:
For low voltage lines, the stays are to be insulated from ground at a height. The insulator used in the stay
wire is called as the stay insulator and is usually of porcelain and is so designed that in case of breakage of
the insulator the guy-wire will not fall to the ground.
FIG: STAY TYPE INSULATOR

28. CHAPTER-8
CIRCUIT BREAKER & ISOLATOR
CIRCUIT BREAKER:
A circuit breaker is the equipment, which can open or close a circuit under normal as well as fault condition.
These circuit breaker breaks for a fault which can damage other instrument in the station.
It is so designed that it can be operated manually (or by remote control) under normal conditions and
automatically under fault condition.
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from
damage caused by over current or overload or short circuit. Its basic function is to interrupt current flow
after protective relays detect a fault.
FIG: SF6 CIRCUIT BREAKER
WORKING PRINCIPLE OF CIRCUIT BREAKER:
The Circuit Breaker mainly consist of fixed contacts and moving contacts. In normal “no” condition of
circuit breaker, these two contacts are physically connected to each other due to applied mechanical pressure
on the moving contacts.
There is an arrangement stored potential energy in the operating mechanism of circuit breaker which is
realized if switching signal is given to the breaker. The potential energy can be stored in the circuit breaker
by different ways like by deforming metal spring, by compressed air or by hydraulic pressure.
TYPES OF CIRCUIT BREAKER:
According to their arc quenching media the circuit breaker can be divided as:
Oil circuit breaker
Air blast circuit breaker
SF6 circuit breaker
Vacuum circuit breaker
OIL CIRCUIT BREAKER:
A high-voltage circuit breaker in which the arc is drawn in oil to dissipate the heat and extinguish the arc;
the intense heat of arc decomposes the oil, generating a gas whose high pressure produced a flow of fresh
fluid through the arc that furnishes the necessary insulation to prevent a re-strike of the arc.

29. The arc is then extinguished, both because of its elongation upon parting of contacts and because of
intensive cooling by the gases of oil vacuum.
FIG: OIL CIRCUIT BREAKER
AIR BLAST CIRCUIT BREAKER:
Fast operations, suitability for repeated operation, auto re-closure, unit type multi break constructions,
simple assembly and modest maintenance are some of the main features of air blast circuit breakers. The
compressors plant necessary to maintain high air pressure in the air receiver. The air blast circuit breakers
are especially suitable for railway and arc furnaces, where the breaker operates repeatedly. Air blast circuit
breaker is used for interconnected lines where rapid operation is desired.
FIG: AIR BLAST CIRCUIT BREAKER
High pressure air at a pressure between 20 to 30 kg/cm2
stored in the air reservoir. Air is taken from the
compressed air system. Three hollow insulator columns are mounted on the reservoir with valves at their
basis. The double arc extinguished chambers are mounted on the top of the hollow insulator chambers. The
current carrying parts connect the three arc extinction chamber to each other in series and the pole to the
neighboring equipment. Since there exists a very high voltage between the conductor and the air reservoir,
the entire arc extinction chambers assembly is mounted on insulators.

30. SF6 CIRCUIT BREAKER:
In such circuit breaker, Sulphur hexafluoride (SF6) gas is used as the arc quenching medium. The
SF6 is an electronegative gas and has a strong tendency to absorb free electrons.
The SF6 circuit breakers have been found to a very effective for high power and high voltage service. SF6
circuit breakers have been developed for voltage 115 KV to 230 KV, power rating
10MVA.
It consists of fixed and moving contacts. It has chamber, contains SF6 gas. When the contacts are opened,
the mechanism permits a high pressure SF6 gas from reservoir to flow towards the arc interruption chamber.
The moving contact permits the SF6 gas to let through these holes.
A typical SF6 circuit breaker consists of interrupter units. Each unit is capable of interrupting currents up to
60 KA and voltage in the range 50-80 KV. A number of units are connected in series according to system
voltage. SF6 breakers are developed for voltages range from 115 to 500 KV and power of 10MVA rating
and with interrupting time of 3 cycles and less.
FIG: SF6 CIRCUIT BREAKER
The use of SF6 circuit breaker is mainly in the substations which are having high input KV input, say above
220KV and more. The gas is put inside the circuit breaker by force i.e. under high pressure. When if the gas
gets decreases there is a motor connected to the circuit breaker. The motor starts operating if the gas went
lower than 20.8 bar. There is a meter connected to the breaker so that it can be manually seen if the gas goes
low. The circuit breaker uses the SF6 gas to reduce the torque produce in it due to any fault in the line. The
circuit breaker has a direct link with the instruments in the station, when any fault occur alarm bell rings.
The spring type of circuit breakers is used for small KV stations. The spring here reduces the torque
produced so that the breaker can function again. The spring type is used for step down side of 132KV to
33KV also in 33KV to 11KV and so on. They are only used in low distribution side.
VACUUM CIRCUIT BREAKER:
Vacuum circuit breakers are the breakers which are used to protect medium and high voltage circuit from
dangerous electrical situations. Like other types of circuit breakers, vacuum circuit breakers are literally
break the circuit so that energy cannot continue flowing through it, thereby preventing fires, power surge
and other problems which may emerge. These devices have been utilized since the 1920s and several
companies have introduced refinements to make them even safer and more effective.

31. FIG: VACUUM CIRCUIT BREAKER
ISOLATORS:
Isolator is used to ensure that an electrical circuit is completely de-energized for service or maintenance.
In Sub-Station, it is often desired to disconnect a part of the system for general maintenance and repairs.
This is accomplished by an isolating switch or isolator.
An isolator is essentially a knife Switch and is design to often open a circuit under no load, in other words,
isolator Switches are operate only when the line is which they are connected carry no load. For example,
consider that the isolator are connected on both side of a circuit breaker, if the isolators are to be opened, the
C.B. must be opened first.
“An Isolator or a dis-connector is a mechanical switch device, which provides in the open position, an
isolating distance in accordance with special requirements. An isolator is capable of opening and closing a
circuit when either negligible current is broken/made or when no significant change in the voltage across the
terminals of each of the poles of isolator occurs. It is also capable of carrying current under normal circuit
conditions and carrying for a specified time, current under abnormal conditions such as those of short
circuit.”
Fig: ISOLATOR
OPERATION OF ELECTRICAL ISOLATOR:
An isolator is a mechanical switch that is manually operated. Depending on the requirement of a given
system, there are different types of isolators. With isolators, one is able to see any open circuit physically as
compared to circuit breakers where no physical observation can be made.
Since no technique for arc quenching exists in isolators, the operation of electrical isolators should only be
carried out when no possible current is flowing through a circuit. An isolator should not be used to open a
completely closed live circuit. Additionally, live circuits should not be completed and closed using an

32. isolator. This is to avoid large amounts of arcing from taking place at the isolator contacts. Hence isolators
should only be opened after a circuit breaker is open and should be closed before closing a circuit breaker.
Electrical isolators can be operated using a motorized mechanism as well as by hand. Hand operation
happens to be cheaper, compared to a motorized arrangement.
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 opened by isolator operation. A complete live
closed circuit must not be opened by isolator operation and also a live circuit must not be closed and
completed by isolator to avoid huge arcing in between isolator contacts. That is why isolator must be open
after circuit breaker is open and these must be closed before circuit breaker is closed. Isolator can be
operated by hand locally as well as by motorized mechanism from remote position. Motorized operation
arrangement costs more compared to hand operation; hence decision must be taken before choosing an
isolator for the system whether hand operated or motor operated economically optimum for the system. For
voltage up to 145 KV system hand operated isolators are used whereas for higher voltage systems like 245
KV or 420 KV and above motorized isolator are used.
FIG: ISOLATOR
TANDEM ISOLATORS:
Tandem isolator, often called split breaker or double breakers, provides two separate circuits in the space of
rectangular sized breaker opening. Every circuit breaker panel has a limited number of circuits available.
The problem is that when the openings are all used up and you still need to add another circuit, what do you
do you? You could change the electrical panel or double up circuits on a breaker, but this could place to
much load on a particular circuit. So what then? The answer that many have found is tandem breaker. This
type of breaker is the same size as any other breaker, but it has its difference.
FIG: TANDEM ISOLATOR

33. CHAPTER-9
CONTROL & RELAY ROOM
The control room has various control panels which shows the information like incoming power, outgoing
power, frequency, time common to all sub-stations, status of various lines(healthy, faulted, under outage or
maintenance), status of various protective instruments like isolators, circuit breaker, temperature of various
instruments, working tap of transformer etc.
The DAS (Data Acquisition System) is used to accumulate the data received from various sources.
The protection system is so fast that it can detect a fault within 30 ms and hence the circuit breaker can be
operated within as less as 80 ms. For 400KV side C.B., one time auto re-closure is allowed in order to clear
the faults automatically.
BATTERY ROOM:
The control panels and relays of the sub-station required DC supply of 110 V.
The DC supply is made with the help of battery bank reserve normally kept in a separate room called
battery room.
The batteries used in this sub-station are Nickel-Cadmium (Ni-Cd) batteries. These batteries are used
due to their advantages like low maintenance, longer life (15-20 years) etc.
Each cell is of 2 V and 300 Ah Capacity.
Fig: BATTERIES at SUB-STATION
Used Of Battery In Sub-Station:
Storage battery system is used in emergency situation for the working of electrical equipments:
To open and close the switch gear
For indication and control
Emergency lighting
Relay and interlocking equipments
 For working of alarm circuit.

34. Protective Relaying:
Protective relays are used to detect defective lines or apparatus and to initiate the operation of circuit
interrupting devices to isolate the defective equipment. Relays are also used to detect abnormal or
undesirable operating conditions other than those caused by defective equipment and either operates an
alarm or initiate operation of circuit interrupting devices. Protective relays protect the electrical system by
causing the defective apparatus or lines to be disconnected to minimize damage and maintain service
continuity to the rest of the system.
There are different types of relays:
i. Over current relay
ii. Distance relay
iii. Differential relay
iv. Directional over current relay
i. Over Current Relay:
Fig: Over Current Relay at Rewa Road, Allahabad Sub-Station
The over current relay responds to a magnitude of current above a specified value. There are four basic types
of construction: They are plunger, rotating disc, static, and microprocessor type. In the plunger type, a
plunger is moved by magnetic attraction when the current exceeds a specified value. In the rotating
induction-disc type, which is a motor, the disc rotates by electromagnetic induction when the current
exceeds a specified value.
Microprocessor relays convert the current to a digital signal. The digital signal can then be compared to the
setting values input into the relay. With the microprocessor relay, various curves or multiple time-delay
settings can be input to set the relay operation. Some relays allow the user to define the curve with points or
calculations to determine the output characteristics.
ii. Distance Relay:
Fig: Distance Relay Control Panel at Rewa
Road, Allahabad Sub-Station

35. The Distance Relays as the overall effect of measuring impedance. The relay operates instantaneously
(within a few cycles) on a 60-cycle basis for values of impedance below the set value. When time delay is
required, the relays energizes a separate time-delay relay or function with the contacts or output of this time-
delay relay or function performing the desired output functions. The relay operates on the magnitude of
impedance measured by the combination of restraint voltage and the operating current passing through it
according to the settings applied to the relay. When the impedance is such that the impedance point is within
the impedance characteristic circle, the relay will trip. The relay is inherently directional. The line
impedance typically corresponds to the diameter of the circle with the reach of the relay being the diameter
of the circle.
iii. Differential Relay:
Fig. Differential Protection Relay at Rewa Road, Allahabad Sub-Station
The differential relay is a current-operated relay that responds to the difference between two or more device
currents above a set value. The relay works on the basis of the differential principle that what goes into the
device has to come out .If the current does not add to zero, the error current flows to cause the relay to
operate and trip the circuit.
The differential relay is used to provide internal fault protection to equipment such as transformers,
generators, and buses. Relays are designed to permit differences in the input currents as a result of current

36. transformer mismatch and applications where the input currents come from different system voltages, such
as transformers.
A current differential relay provides restraint coils on the incoming current circuits. The restraint coils in
combination with the operating coil provide an operation curve, above which the relay will operate.
Differential relays are often used with a lockout relay to trip all power sources to the device and prevent the
device from being automatically or remotely reenergized. These relays are very sensitive. The operation of
the device usually means major problems with the protected equipment and the likely failure in re-
energizing the equipment.
iv. Directional Over current Relay:
Fig. Directional Over Current Relay at Rewa Road, Allahabad Sub-Station
A directional over current relay operates only for excessive current flow in a given direction. Directional
over current relays are available in electromechanical, static, and microprocessor constructions. An
electromechanical overcorrect relay is made directional by adding a directional unit that prevents the over
current relay from operating until the directional unit has operated.
The directional unit responds to the product of the magnitude of current, voltage, and the phase angle
between them or to the product of two currents and the phase angle between them. The value of this product
necessary to provide operation of the directional unit is small, so that it will not limit the sensitivity of the
relay (such as an over current relay that it controls). In most cases, the directional element is mounted inside
the same case as the relay it controls. For example, an over current relay and a directional element are
mounted in the same case, and the combination is called a directional over current relay. Microprocessor
relays often provide a choice as to the polarizing method that can be used in providing the direction of fault,
such as applying residual current or voltage or negative sequence current or voltage polarizing functions to
the relay.

37. CHAPTER-10
WAVE TRAP
Line trap is also known as wave trap. What it does is trapping the high frequency
communication signals sent on the line from the remote sub-station and diverting them to the
telecom/tele-protection panel in the substation control room (through coupling capacitor and
LMU).
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 high frequency communication signals thus obstructs
the flow of these signals in to the substations bus-bars. If there were not to there, then signal
loss in more and communication will be ineffective/probably impossible.
Wave trap is an instrument using for tripping of the wave. The function of this trap is that it
traps the unwanted waves. Its function is of trapping wave. 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 here in the substation.

38. CHAPTER-11
CONCLUSION
Now from this report we can conclude that electricity plays an important role in our life. We
are made aware of how the transmission the transmission of electricity is done. We too came
to know about the various parts of the substation system. The three wings of electrical
system viz. generation, transmission and distribution are connected to each other and that too
very perfectly.
Thus for effective transmission and distribution a substation must: -
Ensure steady state and transient stability
Effective voltage control
Prevention of loss of synchronism
Reliable supply by feeding the network at various points
Fault analysis improvement in respective field
Establishment of economic load distribution

39. REFERENCES
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 www.ieeeexplorer.com