132 KV Substation,
Id no. 42206,
College of Technology,
Govind Ballabh Pant University of
Agriculture & Technology,
Project Report 3
1. Training Order 2
2. Certificate 4
3. Acknowledgement 5
4. Power Transmission Corporation of Uttarakhand Limited 6
5. 132 KV S/s Purukul, Dehradun 8
6. Substation 10
7. Transformer 16
8. Power Line Carrier Communication 19
9. Bus Bars 22
10. Circuit Breakers 23
11. Isolators 27
12. Insulators 28
13. Relays 30
14. Capacitor Bank 33
15. Protection of Substation 34
16. Conclusion 38
17. Bibliography 39
Project Report 4
This is to certify that Mr. Girish Gupta, student of 4th year, Electrical Engineering,
Bachelor of Technology, College of Technology, Govind Ballabh University of
Agriculture & Technology, Pantnagar has undergone summer training at 132KV
Substation, Purukul, Dehradun under Power Transmission Corporation of
Uttarakhand Limited (PTCUL) from 7th July, 2014 to 7th August, 2014 under the
overall guidance of Mr. Prabhash Dabral, S.D.O., Purukul, Dehradun.
Mr. Girish Gupta has successfully completed his training and submitted the
training project report. During the period of training he was found sincere,
punctual and regular. His conduct and behavior was very good.
Mr. Prabhash Dabral
Sub Division Officer
132 KV Substation
Project Report 5
I am very thankful to Mr. Ravindra Kumar, Executive Engineer, Power
Transmission Corporation of Uttarakhand Limited who gave me an opportunity to
undergo training at 132KV Substation, Purukul, Dehradun under Power
Transmission Corporation of Uttarakhand Limited (PTCUL).
I am also thankful to Mr. Prabhash Dabral, Sub Division Officer, 132 KV
Substation, PTCUL who organized the training in a systematic manner and guided
me through the whole training programme.
I would also like to thank all officer/officials who guided and helped me at each
and every step in the training programme.
Id no. 42206
4. POWER TRANSMISSION CORPORATION OF UTTRAKHAND
Project Report 6
Power Transmission Corporation of Uttarakhand Ltd. is the power transmission utility of the
state of Uttarakhand formerly known as Uttaranchal. On 9 November 2000, this 27th state of
the Republic of India was carved out of the Himalayan and adjoining northwestern districts of
Uttar Pradesh per the Uttar Pradesh State Re-organization Act, 2000.
The State of Uttaranchal in exercise of the power granted to it under Section 63(4) of the State
Re-organization Act, 2000, formed two separate companies in power sector - Uttaranchal Jal
Vidyut Nigam Ltd. for generation of hydro-electricity in the state and Uttaranchal Power
Corporation Ltd. for transmission & distribution of electricity in the state.
Enactment of the Electricity Act, 2003, a distinct watershed in the Indian power sector, as it
introduced innovative concepts like power trading, Open Access, Appellate Tribunal, etc., and
special provisions for the rural areas, made it mandatory for all the States to restructure their
As per the provisions of Electricity Act, 2003, the state government separated power
transmission business from UPCL which was left only with distribution of electricity. A new
company by the name & style of Power Transmission Corporation of Uttaranchal Ltd. was
created to handle power transmission business and registered as a Government Company
under Section 617 of Companies Act, 1956 on 27th May, 2004. It started functioning w.e.f. 1st
100% shares of the Company is held by the Government of Uttarakhand either directly or
through its nominees. Authorized capital of the Company at the time of incorporation was Rs.
10 crores divided into one lac equity shares of Rs. 1000 each. At present the authorized capital
of the company is rupees one hundred crores. The Company is managed by the Board of
Directors who meet frequently at least once in every quarter. The day to day management of
the Company is looked after by the Managing Director and other full time Directors of the
Company along with other senior officers. The Corporate and Registered Office of the company
is at Vidyut Bhawan, Near ISBT Crossing, Saharanpur Road, Majra, Dehradun.
Following given is the power line map of Uttarakhand which shows various installed substations
of different capacities and transmission lines in Uttarakhand. It also indicates the position of the
new upcoming substations in the different regions.
Power and Transmission Line Map of Uttarakhand
Project Report 7
5. 132 KV SUBSTATION, PURUKUL, DEHRADUN
The 132 KV substation was commissioned in the year 27th March, 1983.
There are two main 132 KV bus incoming for the substation. These buses are:-
1. 132 KV Purukul-Dhalipur Line
2. 132 KV Purukul-Majra Line
Now the transmission line first parallel connected with lightning arrester to diverge surge,
followed by CVT connected parallel. CVT measures voltage and steeps down from 132KV to
63.5 Volts A.C. for control panel, at the location a wave trap is connected to carrier
communication at higher frequencies. A current transformer is connected in series with line
which measure current and step down current at ratio 800:400:200:1 for control panel.
Switchgear equipment is provided, which is the combination of a circuit breaker having an
isolator at each end. Two transformers are connected to main bus. The main bus has total
capability of 60 MVA for 132 KV, which is subdivided into two transformer capacity of 60 MVA
(40MVA + 20MVA) parallel connected for 132KV.
In addition to the Main bus, Transfer Bus is also provided in the substation in case any
maintenance work is to be carried out on the main bus or there is a glitch in the main bus.
After the Main bus, lightning arresters, current transformers, isolators and circuit breakers
before the transformers are provided. Current Transformers steps down current at ratio
400:200:1 for control panel. Then Transformer step downs voltage from 132KV to 33KV. The
main bus is then again provided with switchgear equipment & a current transformer. This gives
way to six feeders transmitting power to various places. The main bus is connected to jack bus
or transfer bus through a bus coupler & 33KV is provided with switchgear equipment. This gives
way to feeders transmitting power to
Project Report 8
1. Opto Electronics
2. Anarwala I
3. Anarwala II
4. Mussoorie I
5. Mussoorie II
6. I.T. Park
A step down transformer of 33KV/440V is connected to control panel to provide supply to the
equipments of the substation.
Capacitor bank is connected to main bus of 33KV. It is provided to improve power factor &
voltage profile. Capacitor Bank comprises of two units of 5 MVAR making total capacity of 10
At present, an extra 20 MVA transformer is being currently installed at the substation.
Also an additional 132 KV Purukul-Bindal Line is now being connected to the substation.
Project Report 9
Project Report 10
A substation is a part of an electrical generation, transmission and distribution system.
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. 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. A substation
may include transformers to change voltage levels between high transmission voltages and
lower distribution voltages, or at the interconnection of two different transmission voltages.
Substations are classified by two broad categories:-
1. According to the service requirement:
Power factor correction substation
Frequency change substation
2. According to the constructional features:
Pole mounted substation
They are known as transformer substations as because transformer is the main component employed to
change the voltage level, depending upon the purposed served transformer substations may be
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a) STEP UP SUBSTATION
The generation voltage is steeped up to high voltage to affect economy in transmission of
electric power. These are generally located in the power houses and are of outdoor
b) PRIMARY GRID SUBSTATION
Here, electric power is received by primary substation which reduces the voltage level
to 33KV for secondary transmission. The primary grid substation is generally of outdoor
c) SECONDARY SUBSTATIONS
At a secondary substation, the voltage is further steeped down to 11KV. The 11KV lines
runs along the important road of the city. The secondary substations are also of outdoor
d) DISTRIBUTION SUBSTATION
These substations are located near the consumer’s localities and step down to 400V, 3-
phase, 4-wire for supplying to the consumers. The voltage between any two phases is
400V & between any phase and neutral it is 230V.
1. Each circuit is protected by its own circuit breaker and hence plant outage does not
necessarily result in loss of supply.
2. A fault on the feeder or transformer circuit breaker causes loss of the transformer and
feeder circuit, one of which may be restored after isolating the faulty circuit breaker.
3. A fault on the bus section circuit breaker causes complete shutdown of the substation.
All circuits may be restored after isolating the faulty circuit breaker.
4. Maintenance of a feeder or transformer circuit breaker involves loss of the circuit.
5. Introduction of bypass isolators between bus bar and circuit isolator allows circuit
breaker maintenance facilities without loss of that circuit.
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STEPS IN DESIGNING SUBSTATION
The First Step in designing a Substation is to design an Earthing and Bonding System.
Earthing and Bonding
The function of an earthing and bonding system is to provide an earthing system connection to
which transformer neutrals or earthing impedances may be connected in order to pass the
maximum fault current. The earthing system also ensures that no thermal or mechanical
damage occurs on the equipment within the substation, thereby resulting in safety to operation
and maintenance personnel. The earthing system also guarantees equipotent bonding such
that there are no dangerous potential gradients developed in the substation.
In designing the substation, three voltages have to be considered these are:
1. Touch Voltage
This is the difference in potential between the surface potential and the
potential at earthed equipment whilst a man is standing and touching the
2. Step Voltage
This is the potential difference developed when a man bridges a distance of 1m
with his feet while not touching any other earthed equipment.
3. Mesh Voltage
This is the maximum touch voltage that is developed in the mesh of the earthing
Substation Earthing Calculation Methodology
Calculations for earth impedances, touch and step potentials are based on site measurements
of ground resistivity and system fault levels. A grid layout with particular conductors is then
analyzed to determine the effective substation earthing resistance, from which the earthing
voltage is calculated.
In practice, it is normal to take the highest fault level for substation earth grid calculation
purposes. Additionally, it is necessary to ensure a sufficient margin such that expansion of the
system is catered for.
To determine the earth resistivity, probe tests are carried out on the site. These tests are best
performed in dry weather such that conservative resistivity readings are obtained.
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Bare copper conductor is usually used for the substation earthing grid. The copper bars
themselves usually have a cross-sectional area of 95 square millimeters, and they are laid at a
shallow depth of 0.25-0.5m, in 3-7m squares. In addition to the buried potential earth grid, a
separate above ground earthing ring is usually provided, to which all metallic substation plant is
Connections to the grid and other earthing joints should not be soldered because the heat
generated during fault conditions could cause a soldered joint to fail. Joints are usually bolted.
3. Earthing Rods
The earthing grid must be supplemented by earthing rods to assist in the dissipation of earth
fault currents and further reduce the overall substation earthing resistance. These rods are
usually made of solid copper, or copper clad steel.
Switchyard Fence Earthing
The switchyard fence earthing practices are possible and are used by different utilities. These
a) Extend the substation earth grid 0.5m-1.5m beyond the fence perimeter. The fence is
then bonded to the grid at regular intervals.
b) Place the fence beyond the perimeter of the switchyard earthing grid and bond the
fence to its own earthing rod system. This earthing rod system is not coupled to the
main substation earthing grid.
CONDUCTORS USED IN SUBSTATION DESIGN
An ideal conductor should fulfill the following requirements:
a) Should be capable of carrying the specified load currents and short time currents.
b) Should be able to withstand forces on it due to its situation. These forces comprise self-weight,
and weight of other conductors and equipment, short circuit forces and
atmospheric forces such as wind and ice loading.
c) Should be corona free at rated voltage.
d) Should have the minimum number of joints.
e) Should need the minimum number of supporting insulators.
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f) Should be economical.
The most suitable material for the conductor system is copper or aluminums. Steel may be used
but has limitations of poor conductivity and high susceptibility to corrosion.
In an effort to make the conductor ideal, three different types have been utilized, and these
include: Flat surfaced Conductors, Stranded Conductors, and Tubular Conductors .
OVERHEAD LINE TERMINATIONS
Two methods are used to terminate overhead lines at a substation.
a) Tensioning conductors to substation structures or buildings
b) Tensioning conductors to ground winches.
The choice is influenced by the height of towers and the proximity to the substation. The
following clearances should be observed:
VOLTAGE LEVEL MINIMUM GROUND CLEARANCE
less than 11kV 6.1m
11kV - 20kV 6.4m
20kV - 30kV 6.7m
greater than 30kV 7.0m
Clearance in accordance with voltage value
STANDARD SIZES OF CONDUCTOR FOR LINES OF VARIOUS VOLTAGES
The following sizes have now been standardized by CEA for transmission lines of different
Project Report 15
1. For 440 KV Lines
Twin 'Moose' ACSR having 7-Strands of steel of dia 3.53 mm and 54-Strands of
Aluminum of dia 3.53 mm.
2. For 220 KV Lines
'Zebra' ACSR having 7-strand of steel of dia 3.18 mm and 54-Strands of Aluminum of dia
3. For 132 KV Lines
'Panther' ACSR having 7-strands of steel of dia 3.00 mm and 30-Strands of Aluminum of
dia 3.00 mm.
Project Report 16
Transformer is a static machine, which transforms the potential of alternating current at same
frequency. It means the transformer transforms the low voltage into high voltage & high
voltage to low voltage at same frequency. It works on the principle of static induction principle.
When the energy is transformed into a higher voltage, the transformer is called step up
transformer but in case of other is known as step down transformer.
TYPES OF TRANSFORMERS
1. Power Transformer
It is used for the transmission purpose at heavy load, high voltage greater than 33 KV &
100% efficiency. It also having a big in size as compare to distribution transformer, it
used in generating station and Transmission substation at high insulation level. They can
be of two types: Single Phase Transformers and Multi Phase Transformers.
2. Instrument Transformers
These transformers are used for the measurement purposes at that points where
standard voltmeters and ammeters cannot be used. They are of two types:-
a) CURRENT TRANSFORMER
A current transformer (CT) is used for measurement of alternating electric
currents. When current in a circuit is too high to apply directly to measuring
instruments, a current transformer produces a reduced current accurately
proportional to the current in the circuit, which can be conveniently connected
to measuring and recording instruments. A current transformer isolates the
measuring instruments from what may be very high voltage in the monitored
Project Report 17
b) POTENTIAL OR VOLTAGE TRANSFORMER
Voltage transformers (VT) (also called potential transformers (PT)) are a parallel
connected type of instrument transformer, used for metering and protection in
high-voltage circuits or phasor phase shift isolation. They are designed to present
negligible load to the supply being measured and to have an accurate voltage
ratio to enable accurate metering. A potential transformer may have several
secondary windings on the same core as a primary winding, for use in different
metering or protection circuits.
3. Auto Transformers
An autotransformer is an electrical transformer with only one winding. The "auto"
prefix refers to the single coil acting on itself and not to any kind of automatic
mechanism. In an autotransformer, portions of the same winding act as both the
primary and secondary sides of the transformer. The winding has at least
three taps where electrical connections are made. Autotransformers have the
advantages of often being smaller, lighter, and cheaper than typical dual-winding
transformers, but the disadvantage of not providing electrical isolation.
Project Report 18
4. On the basis of working
On the above basis, transformers are of two types: Step up Transformer and Step
5. Distribution Transformers
A distribution transformer is a transformer that provides the final voltage
transmission in the electrical power distribution system, stepping down voltage to
the level used by customers.
8. POWER LINE CARRIER COMMUNICATION (PLCC)
Reliable & fast communication is necessary for safe efficient & economic power supply. To
reduce the power failure in extent & time, to maintain the interconnected grid system in
optimum working condition; to coordinate the operation of various generating unit
communication network is indispensable for state electricity board.
In state electricity boards, the generating & distribution stations are generally located at a far
distance from cities where P & T communication provided through long overhead lines in
neither reliable nor quick.
Power-line communication (PLC) carries data on a conductor that is also used simultaneously
for AC electric power transmission or electric power distribution to consumers.
By using the existing AC power lines as a medium to transfer the information, it becomes easy
to connect the houses with a high speed network access point without installing new wirings.
This technology has been in wide use since 1950 and was mainly used by the grid stations to
transmit information at high speed.
PRINCIPLE OF PLCC
Power-line communications systems operate by adding a modulated carrier signal to the wiring
system. All type of information is modulated on carried wave at frequency 50Hz to 500 KHz. The
modulated HF carrier fed into the power line conductor at the sending end and filtered out
again at the respective stations. Long earlier system double side band amplitude modulation
was more common but the present amplitude modulated system.
Since high voltage power lines are designed to carry large quantities of energy on the high
voltage and the communication system at low voltage, they cannot be directly connected to
high voltage lines. Suitably designed coupling equipments have therefore to be employed which
will permit the injection of high frequency carrier signal without undue loss and with absolute
protection of communication equipments or operating personal from high voltage hazard.
Project Report 19
Therefore, the coupling equipment essentially comprises the following:
1. Wave Trap or Line Trap
Wave trap is connected in series with power line between the point of connection of
coupling capacitor and S/S. Wave trap offers negligible impedance to HF carrier. Wave
trap stands electromechanically and thermally for short circuit current in the event of
fault on the line. On the basis of blocking frequency bank, the wave trap can be
a) All wave
Project Report 20
b) Single Frequency
c) Double Frequency’
d) Broad Band
2. Coupling Capacitor
The modulated carrier is let into power line through coupling capacitor specially
designed to with stand line voltage under all-weather condition. The upper end of the
coupling capacitor is connected directly to the line and the lower end is connected to
the ground through a carrier frequency chock coil or drain coil. Thus coupling capacitor
forms the link between the PLCC equipment and power line. The coupling capacitor
used in UPSEB is 2200pf capacitance.
The coupling capacitor are designed for outdoor use and hence to withstand normal
atmospheric phenomenon such as temperature & humidity changes, rain, snow,
anticipated wind load, nominal wire tension etc. at full rated voltage. In some case
capacitive voltage transformers (CVT) used as a source of line voltage for metering and
protection as also used coupling capacitor for PLCC.
3. Protective Device of Coarse Voltage Arrestor
This is connected across the primary of the coupling filter i.e. one end is connected to
the bottom of the coupling capacitor and other end is earthed. This is provided to
protect the coupling filter against line surges. An air gap is provided, where voltage of
the order of 1.8 to 2KV as observed across due to lighting etc. on line.
4. Coupling of Filter
The coupling filter is inserted between the low voltage terminal of the coupling
capacitor and the carrier frequency connection of the carrier terminal. Sometime an
earth switch is also provided with this unit. This unit mainly performs two functions;
firstly it isolates the connection of equipment from the power line. Secondly it serves to
match characteristic impedance of the power line to that of the H.F. cable to
5. H. F. Cable
H.F. cable normally used to connect the coupling filter to another coupling terminal.
The cable is insulated to withstand the test voltage of 4KV. The impedance of this H.F.
cable is so as to match with the output of the PLCC terminal and secondary impedance
of coupling filter.
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APPLICATION OF PLCC
PLCC technology can be deployed into different types of applications in order to provide
economic networking solutions. Hence merging with other technologies it proves useful in
different areas. These are few key areas where PLC communications are utilized:
a. Transmission & Distribution Network: PLCC was first adopted in the electrical transmission
and distribution system to transmit information at a fast rate.
b. Home control and Automation: PLCC technology is used in home control and automation.
This technology can reduce the resources as well as efforts for activities like power
management, energy conservation, etc.
c. Entertainment: PLCC is used to distribute the multimedia content throughout the home.
d. Telecommunication: Data transmission for different types of communications like
telephonic communication, audio, video communication can be made with the use of PLCC
e. Security Systems: In monitoring houses or businesses through surveillance cameras, PLCC
technology is far useful.
f. Automatic Meter Reading – Automatic Meter reading applications use the PLCC
technology to send the data from home meters to Host Central Station.
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When numbers of generators or feeders operating at the same voltage have to be directly
connected electrically, bus bar is used as the common electrical component. Bus bars are made
up of copper rods operate at constant voltage. The following are the important bus bars
arrangements used at substations:
Single bus bar system
Single bus bar system with section alisation.
Duplicate bus bar system
In large stations it is important that break downs and maintenance should interfere as little as
possible with continuity of supply to achieve this, duplicate bus bar system is used. Such a
system consists of two bus bars, a main bus bar and a spare bus bar with the help of bus
coupler, which consist of the circuit breaker and isolator.
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 neces sary on supply side of circuit
breakers, in order to ensure isolation of the circuit breaker from live parts for the purpose of
A transfer isolator is used to transfer main supply from main bus to transfer bus by using bus
coupler (combination of a circuit breaker with two isolators), if repairing or maintenance of any
section is required.
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10. CIRCUIT BREAKERS
A circuit breaker is an automatically operated electrical switch designed to protect an electrical
circuit from damage caused by overload or short circuit. Its basic function is to detect a fault
condition and interrupt current flow. Unlike a fuse, which operates once and then must be
replaced, a circuit breaker can be reset (either manually or automatically) to resume normal
operation. Circuit breakers are made in varying sizes, from small devices that protect an
individual household appliance up to large switchgear designed to protect high voltage circuits
feeding an entire city. There are different types of circuit breakers which are:-
1. Low-voltage circuit breakers
Low-voltage (less than 1,000 VAC) types are common in domestic, commercial and
industrial application, and include Miniature Circuit Breaker (MCB) and Molded Case
Circuit Breaker (MCCB).
2. Magnetic circuit breakers
Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force increases
with the current. Certain designs utilize electromagnetic forces in addition to those of
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3. Thermal magnetic circuit breakers
Thermal magnetic circuit breakers, which are the type found in most distribution
boards, incorporate both techniques with the electromagnet responding
instantaneously to large surges in current (short circuits) and the bimetallic strip
responding to less extreme but longer-term over-current conditions. The thermal
portion of the circuit breaker provides an "inverse time" response feature, which trips
the circuit breaker sooner for larger over currents.
4. Common trip breakers
Three-pole common trip breaker for supplying a three-phase device. This breaker has a
2A rating. When supplying a branch circuit with more than one live conductor, each live
conductor must be protected by a breaker pole. To ensure that all live conductors are
interrupted when any pole trips, a "common trip" breaker must be used. These may
either contain two or three tripping mechanisms within one case, or for small breakers,
may externally tie the poles together via their operating handles.
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5. Air circuit breakers
Rated current up to 6,300 A and higher for generator circuit breakers. Trip
characteristics are often fully adjustable including configurable trip thresholds and
delays. Usually electronically controlled, though some models
are microprocessor controlled via an integral electronic trip unit. Often used for main
power distribution in large industrial plant, where the breakers are arranged in draw-out
enclosures for ease of maintenance.
6. Vacuum circuit breakers
With rated current up to 6,300 A, and higher for generator circuit breakers. These
breakers interrupt the current by creating and extinguishing the arc in a vacuum
7. Oil circuit breakers
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. They are further of two
types: Bulk Oil Circuit Breaker (BOCB) and Minimum Oil Circuit Breaker (MOCB).
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8. Sulfur hexafluoride (Sf6) high-voltage circuit breakers
A sulfur hexafluoride circuit breaker uses contacts surrounded by sulfur hexafluoride
gas to quench the arc. They are most often used for transmission-level voltages and
may be incorporated into compact gas-insulated switchgear.
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In electrical engineering, a disconnector, disconnect switch or isolator switch is used to ensure
that an electrical circuit is completely de-energized for service or maintenance. Such switches
are often found in electrical distribution and industrial applications, where machinery must
have its source of driving power removed for adjustment or repair. High-voltage isolation
switches are used in electrical substations to allow isolation of apparatus such as circuit
breakers, transformers, and transmission lines, for maintenance. The disconnector is usually
not intended for normal control of the circuit, but only for safety isolation. Disconnector can be
operated either manually or automatically (motorized disconnector).
Unlike load break switches and circuit breakers, disconnectors lack a mechanism for
suppression of electric arc, which occurs when conductors carrying high currents are electrically
interrupted. Thus, they are off-load devices, intended to be opened only after current has been
interrupted by some other control device. Safety regulations of the utility must prevent any
attempt to open the disconnector while it supplies a circuit. Standards in some countries for
safety may require either local motor isolators or lockable overloads (which can be padlocked).
Disconnectors have provisions for a padlock so that inadvertent operation is not possible
(lockout-tag out). In high-voltage or complex systems, these padlocks may be part of a trapped-key
interlock system to ensure proper sequence of operation. In some designs, the isolator
switch has the additional ability to earth the isolated circuit thereby providing additional safety.
Such an arrangement would apply to circuits which inter-connect power distribution systems
where both ends of the circuit need to be isolated.
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An electrical insulator is a material whose internal electric charges do not flow freely, and
therefore make it very hard to conduct an electric current under the influence of an electric
field. The insulator serves two purposes. They support the conductors (bus bar) and confine the
current to the conductors. The most common used material for the manufacture of 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.
Different types of insulator are:-
Pin type insulator
As the name suggests, the pin type insulator is mounted on a pin on the cross -arm on
the pole. There is a groove on the upper end of the insulator. The conductor passes
through this groove and is tied to the insulator with annealed wire of the same material
as the conductor. Pin type insulators are used for transmission and distribution of
electric power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the pin type
insulators become too bulky and hence uneconomical.
For voltages greater than 33 kV, it is a usual practice to use suspension type insulators
shown in Figure. Consist of a number of porcelain discs connected in series by metal
links in the form of a string. The conductor is suspended at the bottom end of this string
while the other end of the string is secured to the cross -arm of the tower. The number
of disc units used depends on the voltage.
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A dead end or anchor pole or tower is used where a straight section of line ends, or
angles off in another direction. These poles must withstand the lateral (horizontal)
tension of the long straight section of wire. In order to support this lateral load, strain
insulators are used. For low voltage lines (less than 11 kV), shackle insulators are used as
strain insulators. However, for high voltage transmission lines, strings of cap-and-pin
(disc) insulators are used, attached to the crossarm in a horizontal direction. When the
tension load in lines is exceedingly high, such as at long river spans, two or more strings
are used in parallel.
In early days, the shackle insulators were used as strain insulators. But now a day, they
are frequently used for low voltage distribution lines. Such insulators can be used either
in a horizontal position or in a vertical position. They can be directly fixed to the pole
with a bolt or to the cross arm.
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In a power system it is inevitable that immediately or later some failure does occur somewhere
in the system. When a failure occurs on any part of the system, it must be quickly detected and
disconnected from the system. Rapid disconnection of faulted apparatus limits the amount of
damage to it and prevents the effects of fault from spreading into the system. For high voltage
circuits relays are employed to serve the desired function of automatic protective gear. The
relays detect the fault and supply the information to the circuit breaker.
The electrical quantities which may change under fault condition are voltage, frequency,
current, phase angle. When a short circuit occurs at any point on the transmission line the
current flowing in the line increases to the enormous value. This result in a heavy current flow
through the relay coil, causing the relay to operate by closing its contacts. This in turn closes the
trip circuit of the breaker making the circuit breaker open and isolating the faulty section from
the rest of the system. In this way, the relay ensures the safety of the circuit equipment from
the damage and normal working of the healthy portion of the system.
Relay works on two main operating principles:-
RELAY USED IN CONTROLLING PANEL OF SUBSTATION
A differential relay is one that operates when vector difference of the two or more
electrical quantities exceeds a predetermined value. If this differential quantity is equal
or greater than the pickup value, the relay will operate and open the circuit breaker to
isolate the faulty section.
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Over Current Relay
This type of relay works when current in the circuit exceeds the predetermined value.
The actuating source is the current in the circuit supplied to the relay from a current
transformer. These relay are used on A.C. circuit only and can operate for fault flow in
the either direction. This relay operates when phase to phase fault occurs.
Earth Fault Relay
This type of relay sense the fault between the lines and the earth. It checks the vector
sum of all the line currents. If it is not equal to zero, it trips.
This type of relay is in the conjunction with main relay. When main relay sense any fault
in the system, it immediately operates the trip relay to disconnect the faulty section
from the section.
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An auxiliary relay is used to indicate the fault by glowing bulb or showing various flags.
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14. CAPACITOR BANK
The load on the power system is varying being high during morning and evening which
increases the magnetization current. This result in the decreased power factor. The low power
factor is mainly due to the fact most of the power loads are inductive and therefore take
lagging currents. The low power factor is highly undesirable as it causes increases in current,
resulting in additional losses. So in order to ensure most favorable conditions for a supply
system from engineering and economic stand point it is important to have power factor as
close to unity as possible. In order to improve the power factor come device taking leading
power should be connected in parallel with the load. One of such device can be capacitor bank.
The capacitors draw a leading current and partly or completely neutralize the lagging reactive
component of load current.
Main functions of Capacitor Bank are:-
Supply Reactive Power
Improve Terminal Voltage
Improve Power Factor
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15. PROTECTION OF SUBSTATION
A lightning arrestor is a device used in power systems and telecommunications systems to
protect the insulation and conductors of the system from the damaging effects of lightning. The
typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning
surge (or switching surge, which is very similar) travels along the power line to the arrester, the
current from the surge is diverted through the arrestor, in most cases to earth.
Transformers are totally enclosed static devices and generally oil immersed. Therefore chances
of fault occurring on them are very easy rare, however the consequences of even a rare fault
may be very serious unless the transformer is quickly disconnected from the system. This
provides adequate automatic protection for transformers against possible faults. Various
protection methods used for transformers are:-
Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors,
equipped with an external overhead oil reservoir called a conservator. The Buchholz Relay is
used as a protective device sensitive to the effects of dielectric failure inside the equipment.
Depending on the model, the relay has multiple methods to detect a failing transformer. On a
slow accumulation of gas, due perhaps to slight overload, gas produced by decomposition
of insulating oil accumulates in the top of the relay and forces the oil level down. A float
switch in the relay is used to initiate an alarm signal. Depending on design, a second float may
also serve to detect slow oil leaks. If an arc forms, gas accumulation is rapid, and oil flows
rapidly into the conservator. This flow of oil operates a switch attached to a vane located in the
path of the moving oil. This switch normally will operate a circuit breaker to isolate the
apparatus before the fault causes additional damage.
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Conservator and Breather
When the oil expands or contacts by the change in the temperature, the oil level goes either up
or down in main tank. A conservator is used to maintain the oil level up to predetermined value
in the transformer main tank by placing it above the level of the top of the tank. Breather is
connected to conservator tank for the purpose of extracting moisture as i t spoils the insulating
properties of the oil. During the contraction and expansion of oil air is drawn in or out through
breather silica gel crystals impregnated with cobalt chloride. Silica gel is checked regularly and
dried and replaced when necessary.
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It has two meter which indicate the temperature of the oil and winding of main tank. If
temperature of oil or winding exceeds than specified value, relay operates to sound an alarm. If
there is further increase in temperature then relay completes the trip circuit to open the circuit
breaker controlling the transformer.
When the transformer is in operation heat is generated due to iron losses the removal of heat is
There are several types of cooling methods, they are as follows:
1. Air natural cooling
In a dry type of self-cooled transformers, the natural circulation of surrounding air is
used for its cooling. This type of cooling is satisfactory for low voltage small
2. Air blast cooling
It is similar to that of dry type self-cooled transformers with to addition that continuous
blast of filtered cool air is forced through the core and winding for better cooling. A fan
produces the blast.
3. Oil natural cooling
Medium and large rating transformers have their winding and core immersed in oil,
which act both as a cooling medium and an insulating medium. The heat produce in the
cores and winding is passed to the oil becomes lighter and rises to the top and place is
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taken by cool oil from the bottom of the cooling tank.
4. Oil blast cooling
In this type of cooling, forced air is directed over cooling elements of transformers
immersed in oil.
5. Forced oil and forced air flow (OFB) cooling
Oil is circulated from the top of the transformers tank to a cooling tank to a cooling
plant. Oil is then returned to the bottom of the tank.
6. Forced oil and water (OWF) cooling
In this type of cooling oil flow with water cooling of the oil in external water heat
exchanger takes place. The water is circulated in cooling tubes in the heat exchanger.
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Now from this report one can conclude that electricity plays an important role in our life. At the
end of the training, I came to know about the various parts of substations and how they are
operated. Also I learnt about how transmission is done in various parts of Uttarakhand.
As evident from the report, a substation plays a very important role in the transmission system.
That’s why various protective measures are taken to protect the substations from various faults
and its smooth functioning. Power Transmission Corporation of Uttarakhand Limited takes
such steps so that a uniform and stable supply of electricity can reach in every part of this state.
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1. Energy efficiency in electrical utilities, Guide book for National certification examination for
energy managers and energy auditors, Bureau of energy efficiency, Ministry of Power, Govt. of
2. General aspect of energy management and energy audit, Guide book for National
certification examination for energy managers and energy auditors, Bureau of energy
efficiency, Ministry of Power, Govt. of India, 2003.