1. The document discusses the equipment used in a 33/11 kV substation, including busbars to connect generators and feeders, insulators to support conductors and confine current, circuit breakers to open circuits during faults, protective relays to detect faults and trip circuit breakers, instrument transformers to step down voltages and currents for metering, meters for monitoring circuit quantities, transformers to step down transmission voltages to distribution levels, capacitor banks to improve power factor, isolating switches to disconnect parts of the system, and lightning arrestors to protect equipment from lightning strikes. 2. A 33/11 kV substation is an important link between the transmission and distribution networks that transforms power from higher transmission voltages to

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Chapter 1
INTRODUCTION
“The assembly of apparatus used to change some characteristics (e.g. Voltage ac to a c freq. p.f. etc)
of electric supply is called sub-station”.
1.1 Electrical Power System:
The present-day electrical power system is A.C .i.e. electrical power is generated, transmitted &
distributed in the form of the alternating current. The electric power is produced at power plant
stations which are located at favourable places generally quite away from the consumers. It is
delivered to the consumers through a large network of transmission 7 distribution. At many places in
the power system, it may be desirable and necessary to change some characteristics e.g. voltage, ac to
dc, frequency, power factor, etc. of electric supply. This accomplished by suitable apparatus called
substation. For example; generation voltage (11 kV or 33 KV) at the power station is set up to high
voltage (say 220 KV or 132 KV) for transmission of electric power. The assembly of apparatus (e.g.
transformer etc.) used for this purpose in the substation. Similarly, near the consumer’s localities, the
voltage may have to be step down to the utilization level. This job is again accomplished by suitable
apparatus called substation
1.2 33/11 KV Substation:
The substation in shirbhavi Sangola 413307, Maharashtra, is the largest power grids in the shirbhavi
Sangola. The most important of any substation is the grounding (Earthling System) of the instruments,
transformers, etc. used in the substation for the safety of the operating personnel as well as for proper
system operation and performance of the protective devices.
1.3 Site Selection & Layout 33/11 KV Substation:
33/11 KV Sub-Station forms an important link between the Transmission network and Distribution
network. It has a vital influence on the reliability of service. Sub-Station is constructed as near as
possible to the load centre. The voltage level of power transmission is decided on the quantum of
power to be transmitted to the load centre.

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1.4Selection of site:
1. Type of Substation:
The category of substation is important for its location. For example a step-up substation,
which is generally a point where power from various sources (generating machines or
generating stations) is pooled and stepped up for long distance transmission, should be
located as close to the generating stations as possible to minimize the transmission
losses.Similarly a step-down substation should be located nearer to the load center to reduce
transmission losses, cost of distribution system and better reliability of supply.
2. Availability of Suitable and Sufficient Land:
The land proposed for a substation should be normally level and open from all sides. It
should not be water logged particularly in rainy season. The site selected for a substation
should be such that approach of transmission lines and their take off can be easily possible
without any obstruction .The places nearer to aerodrome, shooting practice grounds etc.,
should be avoided.
3. Communication Facility:
Suitable communication facility is desirable at a proposed substation both during and after its
construction. It is better, therefore, to select the site along-side on existing road to facilitate an
easier and cheaper transportation.
4. Atmospheric Pollution:
Atmosphere around factories, which may produce metal corroding gases, air fumes,
conductive dust etc., and nearer to sea coasts, where air may be more humid and may be salt
laden, is detrimental to the proper running of power system and therefore substations should
not be located near factories or sea coast.
5. Availability of Essential Amenities to the Staff:
The site should be such where staff can be provided essential amenities like school, hospital,
drinking water, housing etc.

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1.5Types of substation:
The substations may be classified in numerous ways, such as by nature of duties, service
rendered operating voltage, importance, and design.
ClassificationofSubstationsbyNatureofDuties
Step-up or Primary Substations – Such types of substations generate low voltage like 3.3,
6.6, 11, or 33kV. This voltage is stepped up by the help of a step-up transformer for
transmitting the power over large distances. It is located near the generating substation
Primary Grid Substations – This substation lowered the value of primary stepped-up
voltages. The output of the primary grid substation acts as the input of the secondary
substations. The secondary substation is used for stepping down the input voltage to more
lower for further transmission.
Step-down or Distribution Substations – This substation is placed near the load center
where the primary distribution is stepped down for sub-transmission. The secondary
distribution transformer feeds the consumer through the service line
Classificationof SubstationsbyServiceRendered
Transformer substations – In such type of substation transformers are installed for
transforming the power from one voltage level to another level as per need.
Switching Substations – The substations use for switching the power line without disturbing
the voltage is known as the switching substations. This type of substation is placed between
the transmission line.
Converting Substations – In such types of substations, AC power converting into DC power
or vice versa or it can convert the high frequency to lower frequency or vice versa.
ClassificationofSubstationsbyOperatingVoltage
High Voltage Substations (HV Substations) – Involving voltages between 11 kV and 66
KV.
Extra High Voltage Substations – Involving voltages between 132 kV and 400 KV.
Ultra High Voltage – Operating voltage above 400 K

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Chapter 2
EQUIPMENTS IN A 33/11 KV 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. 33/11 KV Sub-Station has the
following major equipment.
2.1 Busbar :
(Figure2.1. Bus Bar)
When numbers of generators or feeders operating at the same voltage have to be directly
connected electrically, the bus bar is used as the common electrical component. Bus bars are
made up of copper rods operate at a constant voltage.

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In substations, it is often desired to disconnect a part of the system for general maintenance
and repairs. An isolating switch or isolator accomplishes this. Isolator operates under no-load
condition. It does not have any specified current breaking capacity or current making
capacity. In some cases, isolators are used to breaking charging currents or transmission lines.
While opening a circuit, the circuit breaker is opened first then isolator while closing a circuit
the isolator is closed first, then circuit breakers. Isolators are necessary on the supply side of
circuit breakers, in order to ensure isolation of the circuit breaker from live parts for the
purpose of maintenance.
2.2 Insulators:
The insulator serves two purposes. They support the conductors (bus bar) and confine the
current to the conductors. The most commonly used material for the manufacture of the
insulator is porcelain. There are several types of insulators (e.g. pin type, suspension type,
post insulator, etc.) and their use in substation will depend upon the service requirement. For
example, post insulator is used for bus bars. A post insulator consists of a porcelain body,
cast iron cap, and flanged cast iron base. The hole in the cap is threaded so that bus bars can
be directly bolted to the cap.
Types of Insulators:-
1. Pin Insulator
2. Suspension Type Insulator
3. Strain Insulator
4. Stay Insulator
5. Shackle Insulator
(Figure2.2.insulators)

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The materials generally used for the insulating purpose is called insulating material. For
successful utilization, this material should have some specific properties as listed below-
1. It must be mechanically strong enough to carry the tension and weight of conductors.
2. It must have a very high dielectric strength to withstand the voltage stresses in the
High Voltage system.
3. It must possess high Insulation Resistance to prevent leakage current to the earth.
4. The insulating material must be free from unwanted impurities.
5. It should not be porous.
6. There must not be any entrance on the surface of the electrical insulator so that the
moisture or gases can enter in it.
7. There physical as well as electrical properties must be less effected by changing
temperature.
2.3 Circuit breaker:
(Figure2.4. oil circuit breaker)

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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 the arc decomposes the oil, generating a gas whose high pressure produces a
flow of fresh fluid through the arc that furnishes the necessary insulation to prevent a restrike of the
arc. The arc is then extinguished, both because of its elongation upon parting of contacts and because
of intensive cooling by the gases and oil vapor.
Types of Circuit Breakers:-
1. Electric Circuit Breaker
2. Arc in Circuit Breaker
3. Vacuum Arc
4. Oil Circuit Breaker
5. Air Circuit Breaker
6. Vacuum Circuit Breaker
The circuit breakers are such types of switches utilized for closing or opening circuits at the
time when a fault occurs within the system. The circuit breaker has 2 mobile contacts which
are in OFF condition in normal situations. At the time when any fault occurs in the system, a
relay is sending the tripped command to the circuit breaker which moves the contacts apart,
hence avoiding any damage to the circuitry.
2.4 Protective relay:
(Figure2.5. 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

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condition in the electrical circuit by constantly measuring the electrical quantities, which are
different under normal and fault conditions. The electrical quantities which may change
under fault condition are voltage, current, frequency, and phase angle. Having detected the
fault, the relay operates to close the trip circuit of C.B.
Types of the relay:
Based on the actuating parameter the protection relay can be categorized as-
1. Current relays.
2. Voltage relays.
3. Frequency relays.
4. Power relays etc.
Based on Characteristic the protection relay can be categorized as:
1. Definite time relays
2. Inverse time relays with definite minimum time(IDMT)
3. Instantaneous relays.
2.5 Instrument Transformer:
The line in Substation operates at high voltage and carries the 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 satisfactorily if
mounted directly on the power lines. This difficulty is overcome by installing Instrument
transformer, on the power lines. There are two types of instrument transformers.
2.5.1 Current Transformer:
(Figure 2.6.1. current transformer)

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A current transformer is a device that is used for the transformation of current from a higher
value into a proportionate current to a lower value. It transforms the high voltage current into
the low voltage current due to which the heavy current flows through the transmission line is
safely monitored by the ammeter.
2.5.2 Voltage Transformer:
(Figure 2.6.2. voltage transformer)
The potential transformer may be defined as an instrument transformer used for the
transformation of voltage from a higher value to a lower value. This transformer step down
the voltage to a safe limit value which can be easily measured by the ordinary low voltage
instrument like a voltmeter, wattmeter and watt-hour meters, etc.

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2.6 Metering and Indicating Instruments:
(Figure2.7. metering instruments)
There are several metering and indicating Instrument (e.g. Ammeters, Voltmeters, 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.
Ammeters, Voltmeters, Wattmeters, kWh meters, KVARH meters, power factor meters
reactive volt-amperes meters are installed in substations to control and maintain a watch over
the current flowing through the circuits and over the power loads.

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2.7 Transformer:
There are three transformers in the incoming feeders so that the three lines step down at the
same time. In the case of a 220KV or more KV line station, autotransformers are used. In
while in case of lower KV lines such as less than 132KV line double winding transformers
are used. i.e. (33/11KV)
(Figure 2.8.5 KVA transformer)
The transformer is a static device that works on the principle of electromagnetic induction. It
is used for transferring the electrical power from one circuit to another without any variation
in their frequency. In electromagnetic induction, the transfer of energy from one circuit to
another takes place with the help of the mutual induction. i.e the flux induced in the primary
winding is linked with the secondary winding.
According to Faraday’s law of electromagnetic induction, there will be an EMF induced in
the second winding. If the circuit of this secondary winding is closed, then a current will flow
through it. This is the basic working principle of a transformer. Let us use electrical symbols

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to help visualize this. The winding which receives electrical power from the source is known
as the ‘primary winding’. In the diagram below this is the ‘First Coil’.
The winding which gives the desired output voltage due to mutual induction is commonly
known as the ‘secondary winding’. This is the ‘Second Coil’ in the diagram above.
A transformer that increases the voltage between the primary to secondary windings is
defined as a step-up transformer. Conversely, a transformer that decreases voltage between
the primary to secondary windings is defined as a step-down transformer.
While the diagram of the transformer above is theoretically possible in an ideal transformer it
is not very practical. This is because in the open air only a very tiny portion of the flux
produced from the first coil will link with the second coil. So the current that flows through
the closed circuit connected to the secondary winding will be extremely small (and difficult
to measure).
The rate of change of flux linkage depends upon the amount of linked flux with the second
winding. So ideally almost all of the flux of primary winding should link to the secondary
winding. This is effectively and efficiently done by using a core type transformer. This
provides a low reluctance path common to both of the windings.

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2.8 Capacitor bank attached to the bus:
(Figure2.9. capacitor bank)
Reactive loads cause current and voltage to shift in phase by up to 90 degrees, Inductive
loads such as motors cause the current to lag the voltage. This whats called the power factor
and cause significant power loss in power transmission. Ideally, the current should be in
phase with the voltage. Capacitors act as a reactive load in the opposite way than inductive

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loads do. By selectively switching in parts of capacitor banks in the substation the power
factor can be brought closer to being in phase and thus reduce power loss. When the PF goes
too far off it is a contributing factor in blackouts.
The demand for active power is expressed in KiloWatts (kW) or Mega Watts (MW). This
power should be supplied from the electrical generating station. All the arrangements in the
electrical pomes system are done to meet up this basic requirement. Although in alternating
power system, reactive power always comes in to picture. This reactive power is expressed in
Kilo VAR or Mega VAR.
The demand for this reactive power is mainly originated from the inductive load connected to
the system. These inductive loads are generally electromagnetic circuits of electric motors,
electrical transformers, the inductance of transmission and distribution networks, induction
furnaces, fluorescent lightings, etc. This reactive power should be properly compensated
otherwise, the ratio of actual power consumed by the load, to the total power i.e. vector sum
of active and reactive power, of the system becomes quite less.
This ratio is alternatively known as the electrical power factor, and fewer ratios indicate the
poor power factor of the system. If the power factor of the system is poor, the ampere burden
of the transmission, distribution network, transformers, alternators and other equipment
connected to the system, becomes high for required active power. And hence reactive power
compensation becomes so important. This is commonly done by the capacitor bank.

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2.9 Isolating Switch:
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 designed to often open a circuit under no load,
in other words, isolator Switches are operated only when the line is which they are connected
carry no load. For example, consider that the isolator is connected on both sides of a cut
breaker, if the isolators are to be opened, the C.B. must be opened first.
2.10 Lightening arrestors:-
Lightning arrestors with earth switch lightning arrestors after the current transformer are used
so as to protect it from lightening i.e. from high voltage entering into it. This lightning
arrestor has an earth switch, which can directly earth the lightning. The arrestor works at 30°
to 45° angel of the lightening making a cone. The earthing switch can be operated manually,
by pulling the switch towards the ground. This also helps in breaking the line entering the
station by doing so maintenance and repair of any instrument can be performed.

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(Figure 2.9. lightning arresters)
Lightning can create voltage surges in several of the following ways. Lightning can score a
direct hit on your house. It can strike the overhead power line which enters your house, or the
main power line that is blocks away from your home. Lightning can strike branch circuitry
wiring in the walls of your house. Lightning can strike an object near your homes such as a
tree or the ground itself and cause a surge. Voltage surges can be created by the cloud to
cloud lightning near your home. A highly charged cloud that passes over your home can also
induce a voltage surge.
2.11 Line isolator:
The line isolators are used to isolate the high voltage flow through the line into the bus. This
isolator prevents the instruments to get damaged. It also allows the only need for voltage and
rest is earthed by itself.
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

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towers. They support the weight of the suspended wires without allowing the current to flow
through the tower to the ground.

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Chapter 3
SINGLE LINE DIAGRAM

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“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.
1. Lightning arrestors,
2. C V T
3. Wave trap
4. Current transformer
5. Isolators with earth switch
6. Circuit breaker
7. Line isolator
8. BUS
9. Potential transformer with a bus isolator
10. Isolator
11. Current transformer
12. Circuit breaker
13. Lightning arrestors
14. Transformer
15. Lightning arrestors with earth switch
16. Circuit breaker
17. Current transformer
18. Isolator
19. Bus
20. Potential transformer with a bus isolator
21. A capacitor bank attached to the bus.

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CONCLUSION
This vocational training has helped me to understand the deep knowledge of the manufacturing
process of the substation as well as they also get much knowledge about electrical equipment. I have
the factual details about the need for a substation in the power system along with its elements.