A report of 4 week industrial Training At power Transmission Corporation of Uttarakhand Ltd.

1. 1
A REPORT
ON
INDUSTRIAL TRAINING
Report submitted to
G. B. Pant Engineering College, Pauri Garhwal
in partial fulfilment of requirement
For the Degree
Of
Bachelor of Technology
In Electrical Engineering
By
Surendra Singh Rawat
DEPARTMENT OF ELECTRICAL ENGINEERING
GOVIND BALLABH PANT ENGINEERING COLLEGE
PAURI GARHWAL (UTTARAKHAND)-246194

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ACKNOWLEDGEMENT
We cannot achieve anything worthwhile in the field of technical education unless or until the
theoretical education acquired in the classroom is effectively wedded to its practical approach that
is taking place in the modern industries and research institutes. It gives me a great pleasure to
have an opportunity to acknowledge and to express gratitude to those who were associated with
my training at PTCUL.
First of all, I am grateful to our Professor & Head, Training & Placement Department MR.
SANDEEP KUMAR for allowing me to undergo training at prestigious company PTCUL. Here I
should not forget to be thankful to Mr. SUBHASH BHATT for providing me with an opportunity to
undergo my training at. Moreover, for providing me with an opportunity to work & gain
experience. I also owe a great deal to all other vocational trainees & persons who directly or
indirectly were a source of constant help & suggestions for me.
Surendra Singh Rawat
EE, Final Year
ID No.- 152309

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CONTENTS
1. INTRODUCTION 01
1.1 Power Transmission Corporation of Uttarakhand(PTCUL) 01
1.2 Power Map of Uttarakhand 03
1.3 Single Line Diagram Of Existing Transmission System 04
2. Single Line Diagram (SLD) of 132 KV Substation Lal Tappar 05
3. Major Parts of Substation 07
3.1 Switchyard 07
3.2 Control Room 32
3.3 PLC Room 49
3.4 Battery Room 50
4. New Technologies 52
5. Future Extension 54
6. References 55

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1. INTRODUCTION
1.1Power Transmission Corporation of Uttarakhand (PTCUL)
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 SEBs.
As per the provisions of Electricity Act, 2003, the state government separated power
Figure – 1.1 Power Transmission Lines

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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 June, 2004.
The Corporate and Registered Office of the company is at Vidyut Bhawan, Near ISBT
Crossing, Saharanpur Road, Majra, Dehradun.
Following given is the power map and SLD of existing transmission in Uttarakhand which
shows various installed substation of different capacities and transmission line in
Uttarakhand. It also indicates the position of new upcoming substation in the different
regions.

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1.2 Power Map Of Uttarakhand
Figure – 1.2 Power Map Of Uttarakhand

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1.3 Single Line Diagram Of Existing Transmission System
Figure –1.3 SLD Of Existing Transmission System

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1. SINGLE LINE DIAGRAM
Single line diagram is a simplified notation for representing a three-phase power system.
Electrical elements such as circuit breakers, transformers, bus bars, and conductors are
shown by standardized schematic symbols. Instead of representing each of three phases
with a separate line or terminal, only one conductor is represented. It is a form of block
diagram graphically depicting the paths for power flow between entities of the system.
Elements on the diagram do not represent the physical size or location of the electrical
equipment, but it is a common convention to organize the diagram with the same left-to-
right, top-to-bottom sequence as the switchgear or other apparatus represented sub-station
is being fed by a 132 KV line from Rishikesh. A 132 KV line is connected from the Laal
Tappar to the Majra. A 40 MVA transformer is being installed of rating 132/33 KV. The
feeder side consists of 6 feeders each of 33 KV, only 3 feeders are yet utilized in the sub-
station. Details of the feeders are:
1) To Bhaniawala one 33 KV feeder.
2) To Lachhiwala one 33 KV feeder.
3) To Laal Tappar one 33 KV feeder.

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Figure –2.1 SLD Of 132 kv Sub-Station Lal Tappar, Dehradun

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2. MAJOR PARTS OF SUB-STATION
3.1 Switchyard
1. Surge Arrester
A lightning arrester or a surge diverter is a protective device which conducts the high
voltage surges on the power system to the ground. Also, surge arrester is a device to protect
electrical equipment from over–voltage transients caused by external (lightning) or internal
(switching) events. The energy criterion for various insulation material can be compared by
impulse ratio, so that a surge incident on the surge arrester may be bypassed to the ground
instead of passing through the apparatus.
Figure –3.1 Surge Arrester

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In actual practice, it may conduct current to ground even at normal supply due to capacitive
effects. As the resistance R offers high resistance to normal voltage, this current is
extremely small. One end of the diverter is connected to the terminal of the equipment to
be protected and the other end is effectively grounded. The length of the gap is so set that
normal line voltage is not enough to cause an arc across the gap but a dangerously high
voltage will break down the air insulation and form an arc. The property of the non-linear
resistance is that its resistance decreases as the voltage (or current) increases and vice-versa.
2. Instrument transformers
In a modern power system, the circuits operate at very high voltages and carry current of
thousands of amperes. The measuring instruments and protective devices cannot work
satisfactorily if mounted directly on the power lines. This difficulty is overcome by
installing instrument transformers on the power lines. The function of these instrument
transformers is to transform voltages or currents in the power lines to values which are
convenient for the operation of measuring instruments and relays. The most common usage
of instrument transformers is to operate instruments or metering from high voltage or
currents. The primary winding of the transformer is connected to the high voltage or high
current circuit, and the meter or relay is connected to the secondary circuit.
The use of instrument transformers permits the following advantages: (a) They isolate the
measuring instruments and relays from high-voltage power circuits. (b) The leads in the
secondary circuits carry relatively small voltages and currents. This permits to use wires
of smaller size with minimum insulation.
2.1 Potential transformer (P.T.)
It is just like a general-purpose step-down transformer. A potential transformer is
connected with its primary in the power line. The secondary provides for the instruments
and relays a voltage which is a known fraction of the line voltage. The potential transformer
rated 132,000/110V provides a voltage supply for the potential coils of voltmeter and
wattmeter.

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2.2 CAPACITOR VOLTAGE TRANSFORMER (CVT)
A capacitor voltage transformer (CVT or CCVT), is a transformer used in power systems
to step down extra high voltage signals and provide a low voltage signal, for metering or
operating a protective relay.
Figure –3.2 Potential Transformer
Figure –3.3 Circuit Diagram of CVT

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In its most basic form, the device consists of three parts: two capacitors across which the
transmission line signal is split, an inductive element to tune the device to the line
frequency, and a voltage transformer to isolate and further step down the voltage for
metering devices or protective relay. Capacitive voltage transformers exist and are used by
utilities for high-voltage (greater than 66 kV) metering. The CVT is also useful in
communication systems. CVTs in combination with wave traps are used for filtering high-
frequency communication signals from power frequency. This forms a carrier
communication network throughout the transmission network, to communicate between
substations. The CVT is installed at a point after lightning arrester and before wave trap.
PT and CVT both can be used for 11kV and above lines. but in practically for
132KV and above the transformer weight of PT become highly bulky and hence losses are
more. Whereas in CVT instead of the usual transformer weight we use as already said
capacitor series that perform two notable functions:
1) First one gives a low impedance path to PLCC carrier wave frequency which is order of
100-500khz and hence its used for protection and relaying and telemetering purposes.
2) Second one, the voltage drop across each capacitor and hence it is viable to measure the
voltage by using low coiled transformer.
Figure –3.4 Capacitor Voltage Transformer(CVT) between surge arrester and
wave trap

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2.3 Current transformer (C.T.)
A current transformer is a type of transformer that is used to measure AC current. It
produces an alternating current in its secondary which is proportional to AC current in its
primary. Current Transformer are the current sensing units of the power system. The output
of the current transformers are used in electronic equipment and are widely used for
metering and protective relays in the electrical power industry.
The primary of current transformer is connected in the power line. The secondary winding
provides for the instruments and relays a current which is a constant fraction of the current
in the line. The current transformer rated 800/400/1 A supplies current to the current coils
of wattmeter and ammeter
3. Wave Trap
A line trap (HIGH-FREQUENCY STOPPER) is a maintenance-free parallel resonant
circuit, mounted inline on high-voltage(HV) AC transmission power lines to prevent the
transmission of high frequency (40KHZ to 1000KHZ) carrier signals of power line
communication to unwanted destinations. Line trap are cylinder-like structures connected
Figure –3.5 Current Transformer

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in series with HV transmission lines. A line trap is also called a wave trap. The line trap
acts as a barrier or filter to prevent signal losses. Wave trap or line trap is a device that
imposes high impedance for high frequency signals and low impedance for low frequency
signals thus passing only low frequency signals.
Also, a high frequency message signal is being transmitted along with the power line for
the purpose of communication and protection known as carrier protection. This is relevant
in power carrier communication (PLCC) system for communication among various
substation dependence on telecom company network. The signals are primarily
teleportation signal and in addition, voice and data.
4. Isolator-:
An Isolator is a circuit breaking switch which can only be operated (either open or close)
no load. There are three types of isolators used in this particular sub-station depending upon
their names:
Figure –3.6 Wave Trap

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a) Transfer Isolator-: In case of some maintenance work on any of the circuit breaker
or isolator an auxiliary circuit breaker is used (known as bus coupler) a transfer isolator is
used to transfer the supply to the auxiliary bus so that the bus coupler can be used in place
of other circuit breaker. It is also known as tandem isolator.
b) Line Isolator-: A 3-phase isolator connected at the line side is known as line
isolator. A line isolator is an off-load switch that connects the line breaker and the bus. Its
sits between circuit breaker and current transformer.
c) Bus Isolator-: A 3-phase isolator is connected at the bus side is known as bus
isolator. There is no difference in construction and working between line and bus isolator.
Figure –3.7 Transfer Isolator

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Bus side isolator is connected directly in between the main bus. A bus isolator is an off load
switch that connects the line breaker and the bus. It sits between circuit breaker and bus .
5. Circuit Breaker-: The circuit breaker is one of the most important unit of
electrical power system. Circuit breaker is a mechanical switching device capable of
making, carrying and breaking currents under normal circuit conditions and also making ,
carrying for a specified time, and automatically breaking currents under specified abnormal
circuit conditions such as those of short-circuits(faults).The function of the circuit breaker
is to isolate the faulty part of the power system in case of abnormal conditions such as faults.
A protective relay detects abnormal conditions and send a tripping signal to the circuit
breaker. After receiving the trip command from the relay, the circuit breaker isolates the
faulty part of the power system. The protection, continuity and stability of the system
Figure –3.8 Isolator

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depends upon the ability of the circuit breaker to switch line, load and exciting currents and
to interrupt fault current. A circuit breaker is a circuit breaking device that can be operated
at both no-load and full load. The operating mechanism of circuit breaker depends upon the
voltage rating of the line for which it is to be installed and are classified according to arc
quenching medium.
For different voltage ratings on line side and feeder side different circuit breakers are used
which are following:
6. SF6 Circuit Breaker-: This circuit breaker is used at the high voltage side means at
132kv side. As SF6 gas is the arc quenching medium that’s why named as SF6 circuit
breaker. Due to its superior arc quenching properties and better chemical properties than
vacuum and air ,SF6 finds huge applications in high voltage circuit breakers. SF6 has good
dielectric strength and excellent arc quenching property. It is an inert, non- toxic,
Figure –3.9 Design Of Circuit Breaker

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noninflammable and heavy gas. At atmospheric pressure, its dielectric strength is about
2.35 times of that air. SF6 gas because of its excellent insulating and arc-quenching
properties it has revolutionized the design of high and extra high voltage(EHV) circuit
breakers. SF6 circuit breakers are manufactured in the voltage range 3.3KV to 765KV .
RATINGS OF GAS CIRCUIT BREAKER:
RATED VOLTAGE 145KV
RATED NORMAL CURRENT 2000A
RATED SHORT-CIRCUIT BREAKING
CURRENT
40KA
RATED GAS PRESSURE 7Kg/cm sq.(AT 20deg.)
RATED FREQUENCY 50 HZ
RATED MAKING CAPACITY 100 KA
GAS WT. 7.5Kg
TOTAL WT. 1450Kg
Figure –3.10 Operaton Of Circuit Breaker

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7. Vacuum Circuit Breaker-: This circuit breaker is used at the low voltage side
means at 33kv side. In such breakers, vacuum (degree of vacuum being in the range from
10−7 to 10−5 torr) is used as the arc quenching medium. As soon as the arc is produced in
vacuum, it is quickly extinguished due to the fast rate of recovery of dielectric strength in
vacuum.
Figure –3.11 SF6 Circuit Breaker

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RATING OF VACCUM CIRCUIT BREAKER:
RATED VOLTAGE 30KV
RATED CURRENT 1000A
FREQUENCY 50HZ
INSULATION LEVEL 70KV/170KV
S.C BREAKING CURRENT 25KArms
S.C MAKING CURRENT 65KA Pk
OPERATION SEQUENCE O-0.3S-CO-3min--CO
S.C WITHSTAND CURRENT AND
DURATION
25KA , 3sec
8. Bus Coupler-: This is same as that of other circuit breakers (at both 132kv and
33kv sides) in both construction and operating mechanism but used when some
Figure –3.12 Vaccum Circuit Breaker At Low Voltage Side (Feeder Side)

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maintenance work is to be done at any other main circuit breaker thus also known as
auxiliary circuit breaker.
9. Transformer-: Transformer is a static electromagnetic device used to change the
either voltage or current level keeping the total VA constant. In this sub-station following
types transformers are installed:
A 3-phase step down transformer of rating 132kv/33kv is installed at the sub-station.
Transformers are static devices, totally enclosed and generally oil immersed.
Therefore, chances of faults occurring on them are very rare. However, the consequences
of even a rare fault may be very serious unless the transformer is quickly disconnected from
the system. This necessitates to provide adequate automatic protection for transformers
against possible faults. Small distribution transformers are usually connected to the supply
system through series fuses instead of circuit breakers. Consequently, no automatic
protective relay equipment is required. However, the probability of faults on power
transformers is undoubtedly more and hence automatic protection is absolutely necessary.
Common transformer faults. As compared with generators, in which many abnormal
conditions may arise, power transformers may suffer only from :
(i) open circuits
(ii) overheating
(iii) winding short-circuits
e.g. earth-faults, phase-to-phase faults and inter-turn faults.

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An open circuit in one phase of a 3-phase transformer may cause undesirable heating. In
practice, relay protection is not provided against open circuits because this condition is
relatively harmless. On the occurrence of such a fault, the transformer can be disconnected
manually from the system.
Overheating of the transformer is usually caused by sustained overloads or short-circuits
and very occasionally by the failure of the cooling system. The relay protection is also not
provided against this contingency and thermal accessory are generally used to sound an
alarm or control the banks of fans. Winding short-circuits (also called internal faults) on the
Figure –3.13 132kv/33kv Transformer

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transformer arise from deterioration of winding insulation due to overheating or mechanical
injury. When an internal fault occurs, the transformer must be disconnected quickly from
the sy9stem because a prolonged arc in the transformer may cause oil fire. Therefore, relay
protection is absolutely necessary for internal faults. For protection of generators, Merz-
Price circulating-current system is unquestionably the most satisfactory. Though this is
largely true of transformer protection, there are cases where circulating current system
offers no particular advantage over other systems or impracticable on account of the
troublesome conditions imposed by the wide variety of voltages, currents and earthing
conditions invariably associated with power transformers. Under such circumstances,
alternative protective systems are used which in many cases are as effective as the
circulating-current system.
Figure –3.14 Transformer Cooling

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The principal relays and systems used for transformer protection are:
(i) Buchholz devices providing protection against all kinds of incipient
faults i.e. slow-developing faults such as insulation failure of windings, core heating, fall
of oil level due to leaky joints etc.
(ii) Earth-fault relays providing protection against earth-faults only.
(iii) Overcurrent relays providing protection mainly against phase-to-phase
faults and overloading.
(iv) Differential system (or circulating-current system) providing protection
against both earth and phase faults. The complete protection of transformer usually
requires the combination of these systems. Choice of a particular combination of systems
may depend upon several factors such as
(a) size of the transformer
(b) type of cooling
(c) location of transformer in the network
(d) nature of load supplied and
(e) importance of service for which transformer is required.
RATING OF TRANSFORMER(132KV/33KV):
MVA 24/40
VOLTAGE-KV 132/33
TEMPERATURE RISE IN OIL 50 deg. C
TEMPERATURE RISE IN WINDINGS 55 deg. C
TYPES OF COOLING ONAN/ONAF
CORE AND WINDING 38,000Kg
TANK AND FITTING 17,000Kg
OIL WEIGHT 18,000Kg

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TOTAL WEIGHT 75,000Kg
OIL VOLUME 20751
VECTOR GROUP YNyno
FREQUENCY 50 HZ
HV Amps. 104.972/174.955
LV Amps. 419.9/699.2
10.BUSHING-: A Bushing is a hollow insulating liner through which a conductor
may pass. Bushings appear on switchgear, transformer, circuit breakers and other high
voltage equipment.
The bushing is a hollow insulator, allowing a conductor to pass along its center and
connect at both ends to other equipment. Bushings are often made of wet-process fired
porcelain, and length of the bushing.
The inside of the bushing may contain paper insulation and the bushing is often filled
with oil to provide additional insulation. Bushings for medium- voltage and low –voltage
apparatus may be made of resins reinforced with paper. The use of polymer bushings for
high voltage applications is becoming more common.
11.Porcelain bushings and big hollow insulators: - The hollow insulator, porcelain
bushings are used extensively in electrical apparatus. Porcelain bushings is the device that
enables one or several conductors to pass through a partition such as a wall or tank and
insulates the conductors from it. Big porcelain bushing, hollow insulator up to 1000Kv.

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Figure –3.15 Porcelain Bushings And Big Hollow Insulators

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12.Small porcelain bushings: - Small porcelain bushings, hollow insulators are
used as the insulating elements such as the transformer bushings and wall bushings. They
are designed to perform under outdoor and indoor conditions for voltage up to 36Kv
13.Taps or Tap Changer-: The transformer is provided with a tap in order to
adjust the voltage ratio of the transformer. These taps are provided along the winding with
connections to a tap-changing device that makes the physical change in the in-service tap.
The tap changing devices is usually placed on the primary winding to minimize the current
to be switched and can be “off-circuit” Or “on-load’’ type. When the primary voltage is
low, the tap changer reduces correspondingly the number of primary turns to maintain the
secondary voltage constant. Similarly, when the primary voltage is high, the tap changer
Figure – 3.16 Bushing In Transformer

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increases correspondingly the number of primary turns to maintain the secondary voltage
constant.
14. Off-Circuit Tap Changer: - In industrial power system, off-circuit taps are used
with dry-type transformer, liquid-immersed transformer, when they are not connected
directly to the utility power supply. On the primary (high voltage side) of step-down
transformer, four full-capacity taps (five positions) are provided in four 2.5% steps, 2 above
and 2 below normal. The tap-changer mechanism should change the taps on all three phases
simultaneously. Also, it should be operable from ground level, with tap changer position
for padlocking.
15.On- Load Tap-Changer: - On-load tap changers (OLTS) are mostly with oil-
immersed transformer Connected to the utility power supply at a voltage level exceeding
34.5Kv because the majority of the power companies stipulated a voltage variation of +10%
or -10% in the power contract, the tap changer is provided with an equivalent range of
voltage regulation of +10% or -10% in 16 or 32 steps. 16 step tap-changer provides 5/4 %
voltages changes in each step. 32 step tap-changer provides 5/8% voltage change in each
step thus more preferred.
Figure – 3.17 Off-Circuit Tap-Changer

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When the tap-changer design requires an oil-expansion tank, it shall be piped to a separate
compartment in the conservator. A separate tap-changer gas-detector relay is located in
this pipe.
The tap-changing control equipment includes:
1. Control and paralleling equipment
2. Line drop compensation equipment along with the current transformer to provide
voltage control at a point remote from the measuring point.
 Automatic voltage-regulating relay.
 Weather proof control cabinet, accessible from ground level.
16.Insulators: - Overhead line insulators are used to separate line conductors from each
other and from the supporting structures electrically. While designing an insulator the
following considerations are made:
A. The insulators should have high permittivity so it can withstand high electrical
stresses.
B. It should possess high mechanical strength to bear the conductor load under worst
loading conditions.
C. It needs to have a high resistance to temperature changes to reduce damages from
power flashover.
Figure – 3.18 On- Load Tap Changer

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D. The leakage current to earth should be minimum to keep the corona loss radio
interference within reasonable limits.
There are different type of insulators used in overhead line:
Pin Insulator: Pin insulator is earliest developed overhead line insulator, but still popularly
used in power network up to 33kV system.
The pin insulator is supported on a forged steel pin or bolt which is secured to the cress arm
of the supporting structure. The conductor is tied to the insulator on the top groove on
straight line positions and side groove in angle positions by annealed binding wire of the
same material as conductor.
Figure – 3.19 Pin Type Insulator

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Suspension insulator: 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 insulators are developed.
In suspension insulator number of insulators are connected in series to form a string and the
line conductor is carried by the bottom most insulator. Each insulator of suspension string
is called disc insulator because of their disc like shape. Each disc of suspension string
possesses 11kv. So the number of disc used in a string is depends upon the voltage.
Strain insulator: When suspension string is used to sustain extraordinary tensile load of
conductor it is referred as string insulator. When suspension insulator string is placed
horizontally to the ground the it called strain insulator. When there is a dead end or there is
Figure – 3.20 Suspension insulator
Suspension Insulator

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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.
17.Feeders: - To connect the consumer/load end with the substation, we
have feeders. There is no tapping taken out of them. They just connect the consumer area
with the substation.
These are the conductors which are of large current carrying capacity. The feeders connect
the substation to the area where power is to be finally distributed to the consumers. No
tapings are taken from the feeders. The feeder current always remains constant.
In this substation, there are nine feeders which transmits the power to various places.
Figure – 3.21 Feeders Control Panel

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There are three working feeders in the sub-station:
1. Lachiwala
2. Bhaniyawala
3. Lal Tappar

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3.2 Control Room
3.2.1 Protection
Control and Relay panel is most important part of the substation as it works as shield guard
for all substation equipments and electrical network. Moreover, these panels are useful to
control the flow of electricity as per the Voltage class and detect the faults in transmission
lines.
If a fault occurs in an element of power system, an automatic protective device is
needed to be isolate the faulty element as quickly as possible to keep the healthy section of
the system in normal operation. The fault must be cleared within a fraction of a second. If
a short circuit sists on a system for a longer, it may cause damage to some important section
of the system. A heavy short circuit current may cause a fire. It may spread in the system
and damage a part of it. The system voltage may reduce to a low level may lose
synchronism. Thus, an uncleared heavy short circuit may cause the total failure of the
system.
A protective system includes circuit breakers, transducers (CTs and VTs), and protective
relays to isolate the faulty section of power system from the healthy section. A circuit
breaker can disconnect the faulty element of the system when it called upon to do so by the
protective relays. Transducers are used to reduce current and voltages to lower values and
to isolate protective relays from the high voltage of the power system. The function of a
protective relay is to detect and locate a fault and issue a command to the circuit breaker to
disconnect the faulty element. It is a device which senses abnormal conditions on a power
system. The basic electrical quantities which are likely to change during abnormal
conditions are current, voltage, phase angles and frequency. Protective relays utilize one or
more of these quantities to detect abnormal conditions on a power system.

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Relays-: In a power system consisting of generators, transformers, transmission
and distribution circuits, it is inevitable that sooner or later some failure will 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. There are two principal reasons for it.
Firstly, if the fault is not cleared quickly, it may cause unnecessary interruption of service
to the customers. Secondly, rapid disconnection of faulted apparatus limits the amount of
damage to it and prevents the effects of fault from spreading into the system. The detection
of a fault and disconnection of a faulty section or apparatus can be achieved by using fuses
or relays in conjunction with circuit breakers. A fuse performs both detection and
interruption functions automatically but its use is limited for the protection of low-voltage
Figure – 3.22 control panel for protection system

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circuits only. For high voltage circuits relays and circuit breakers are employed to serve
the desired function of automatic protective gear.
A protective relay is a device that detects the fault and initiates the operation of the
circuit breaker to isolate the defective element from the rest of the system. The relays detect
the abnormal conditions in the electrical circuits by constantly measuring the electrical
quantities which are different under normal and fault conditions. The electrical quantities
which may change under fault conditions are voltage, current, frequency and phase angle.
The relay circuit connections can be divided into three parts viz. (i) First part is the
primary winding of a current transformer (C.T.) which is connected in series with the line
to be protected. (ii) Second part consists of secondary winding of C.T. and the relay
operating coil. (iii) Third part is the tripping circuit which may be either A.C. or D.C. It
consists of a source of supply, the trip coil of the circuit breaker and the relay stationary
contacts. All the relays are connected with the 110V D.C. supply.
Different types of relays which are being used in this sub-station are following:
1. Mechanical Relays-: These types of relays use mechanical parts for its operation.
Due to mechanical parts, these relays are slower in operation. Under this category of relays,
the relay used in the substation is only Restricted Earth Fault relay.
1.1 Restricted Earth Fault Relay-: This relay is used for the protection of the
transformer. Restricted earth protection which also known as Differential Earth protection
by which a particular defined zone is protected (restricted). For REF, the neutral point of
the Transformer (star point) is required to be earthed. The REF composed from 4CTs, one
to be installed on the Earthed-Neutral while the remaining 3no. to be for phases (R, Y, B).
The REF arranged as follows: One side of the 4 CTs to be connected together and the other
terminals of the phases CTs to be connected to the first terminal of their operated relays.
The other terminals of the relays to be connected together to the earth relay & the other
Neutral CT lead.
Operation: -
The current passing through the earth relay equal to the difference between the current of
earthed-neutral & the sum (resultant) of the phases current (IR+IY+IB-IN)=0.

38. 38
Therefore, there will be no current through the earth relay unless there a fault occurs within
the protected zone (prior to Phases CTs). If there is an earth fault between the CTs then
some current will bypass the CTs and the sum of the current will not be zero. By measuring
this current imbalance faults can be easily identified and quickly cleared.
2. Numerical Relays-: These relays does not consist of any mechanical moving
parts. The relays are microprocessors based relays which allow them to operate accurately
within no time. With the facilities of easy and smooth settings these kinds of relays are
getting popular now a day in the sub-stations. The following types of protective relays are
used in the sub-station-:
2.1 Over current and earth fault relay-: These relays are of following types-:
a) Directional over current and earth fault relay
b) Non- directional over current and earth fault relay
Design and principle
The combined overcurrent and earth-fault relay is a secondary relay to be connected to
the current transformers of the protected object. The three-phase overcurrent unit and the
earth-fault unit continuously measure the phase currents and the neutral current of the
protected object. On detection of a fault the relay starts, trips the circuit breaker, initiates
auto-reclosing, provides alarm, records fault data etc. in accordance with the application
Figure – 3.23 Restricted Earth Fault Relay

39. 39
and the configured relay functions. When the phase current exceeds the set start current of
the low-set stage I>, the overcurrent unit starts delivering a start signal after a preset 60 ms
start time. When the set operate time at definite time operation or the calculated operate
time at inverse time operation elapses, the overcurrent unit operates. In the same way the
high-set stage I>> of the overcurrent unit starts delivering a start signal after a preset 40 ms
start time, when the set start current is exceeded. When the set operate time elapses, the
overcurrent unit operates. When the earth-fault current exceeds the set start current of the
low-set stage Io>, the earth-fault unit starts delivering a start signal after a preset 60 ms start
time. When the set operate time at definite time operation or the calculated operate time at
inverse time operation elapses, the earth-fault unit operates. In the same way the high-set
stage Io>> of the earth-fault unit starts delivering a start signal after a preset 40 ms start
time, when the set start current is exceeded. When the set operate time elapses, the earth-
fault unit operates. The low-set stage of the overcurrent unit and the low-set stage of the
earth-fault unit may be given definite time or inverse definite minimum time (IDMT)
characteristic. By appropriate configuration of the output relay matrix, the start signals of
the overcurrent and earth-fault units are obtained as contact functions. The start signals can
be used for blocking co-operating protection relays, for signaling and initiating auto-
reclosing. The relay includes one external binary input, which is controlled by an external
control voltage. The function of the control input is determined by selector switches in the
protection relay module. The control input can be used for blocking the operation of one or
more protection stages, for resetting a latched output relay in the manual reset mode or for
enforcing a new set of relay setting parameters by remote control.
This also indicates following functions-:
Applications-: These are used for the selective short-circuit and time overcurrent
protection of radial feeders in distribution networks. The relays are also used for feeder
earth-fault protection in isolated neutral networks and networks with resistively earthed
neutral. Both the overcurrent unit and the earth-fault unit feature two stages: a high-set stage
and a low-set stage.

40. 40
2.2 Differential relay-: Differential relays are basically used for the protection of
transformer winding. It checks the difference between input and output currents of the
transformer. The difference amongst the currents may also be in phase angle or magnitude
or in each. For normal operation, this difference must be zero.
Principle operation of the Differential relay-:
For an example in a power transformer the transformation ratio is 1:1 and (Y-Y)
connection, CT1 and CT2 are connected accordingly. The current flows within the primary
and secondary side of the transformer are equal. Thus a net zero current flows through the
operating coil thus it doesn’t operate.
During external fault condition the net current through the operating coil is zero hence
differential relay will not operate for an external fault.
An internal fault causes a difference in the CT currents and a net current flow through
the operating coil and thus the relay operates.
A numerical differential relay consists of a microprocessor based system which serves
the function of a protective relay for the winding of transformer.
Figure – 3.24 Over Current and Earth Fault Relay

41. 41
Main functions of numerical differential relay-:
a) Differential protection
1) Matching to the vector group.
2) Stabilization under inrush.
3) Stabilization under over fluxing conditions.
b) Thermal overload protection.
c) Over/under voltage protection.
d) Over/under frequency protection.
e) Over excitation protection.
2.3 Distance Relay-: Distance relay is used for the protection of transmission lines.
It uses the principle that, whenever a fault occurs it changes the impedance of the
transmission line, for its operation. It actually measures the impedance of the line from the
fault point to the point it is connected and according to the per km. impedance of the line it
calculates the total length of the transmission line up to the fault point. This relay is also a
microprocessor based numerical relay having different types of indications such as-:
Advantages-:
a) Improves dependability and security.
b) Has self-checking facility.
c) Offers very low burden.
Figure – 3.25 Differential Relay

42. 42
d) More flexible due to programmable capability.
e) Adaptive relaying schemes.
f) Permit historical data storage.
g) Separate connections are not required, zero sequence voltages and currents can be
derived inside the processor.
Main functions of numerical distance relay-:
a) Distance protection.
b) Power swing blocking.
c) Switch on to fault.
d) Phase fault over-current protection.
e) Directional earth fault protection.
f) Sensitive earth fault protection.
g) Overvoltage and under voltage protection.
h) Broken conductor detection.
i) Circuit breaker failure protection.
Other important functions of numerical distance relay-:
a) Control
1) Auto reclosing.
2) Check synchronizing.
b) Monitoring
1) Voltage transformer supervision.
c) System data
1) Sequence of event records.
2) Fault records.
3) Disturbance recorder.

43. 43
2.4 Buchholz relay: - In the field of electric power distribution and transmission, a
Buchholz relay, also called a gas relay or a sudden pressure 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. The relay has two different detection
modes. 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 that also serves 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. Buchholz relays have a test port to allow the
accumulated gas to be withdrawn for testing.
Figure – 3.26 Distance Relay

44. 44
3.2.2 Metering and Monitoring-: Metering and monitoring is done by different
types of indicating and metering instruments such as ammeter, voltmeter, energy meter,
temperature indicator and power measurements. All these instruments are of digital type
hence more accurate and reliable.
1. Ammeter-: Digital ammeters are instruments that measure current flow in
amperes and display current levels on a digital display. These devices provide information
about current draw and current continuity in order to help users troubleshoot erratic loads
and trends. They have both positive and negative leads and feature extremely low internal
resistance.
Figure – 3.27 Buchholz relay

45. 45
Digital ammeters are connected in series with a circuit so that current flow passes through
the meter. Secondary connections of CTs are brought to these ammeters for the
measurement of high currents flowing through the conductors.
Main features of digital ammeters-:
a) Alarm LED.
b) Battery powered.
c) Overload protection.
d) Temperature compensated.
2. Voltmeter-: A digital voltmeter (DVM) measures an unknown input
voltage by converting the voltage to a digital value and then displays the voltage in numeric
form. DVMs are usually designed around a special type of analog-to-digital converter
called an integrating converter.
DVM measurement accuracy is affected by many factors, including temperature, input
impedance, and DVM power supply voltage variations. Less expensive DVMs often have
input resistance on the order of 10 MΩ. Precision DVMs can have input resistances of 1
GΩ or higher for the lower voltage ranges (e.g. less than 20 V). They are connected to the
secondary of the PT for the measurement of high voltage. One voltmeter is required for
each phase.
Figure – 3.28 Digital Ammeter

46. 46
3. 3-Phase energy meter-: An instrument which measures
electrical energy in watt hours, is essentially a wattmeter which accumulates or averages
readings. Digital electronic instruments measure many parameters and can be used where a
wattmeter is needed: volts, current, in amperes, apparent instantaneous power, actual
power, power factor, energy in KW-h over a period of time, and cost of electricity
consumed.
It can show all the important parameters like total active power imported or exported, total
reactive power imported or exported, voltage of each phase, system frequency and also have
the function to show time and date. It can also store data which can be retrieved when
required and data can be easily noted with the help of scanning device.
Figure – 3.29 Digital Voltmeter
Figure – 3.30 3-Phase Energy Meter

47. 47
4. Wattmeter-: The wattmeter is an instrument for measuring the electrical
power (or the supply rate of electrical energy) in watts of any given circuit. It actually
measures VI*cos(ᶲ) which is the active power in the circuit. For higher values of active
power reading is shown in KW or MW. A modern digital electronic wattmeter/energy meter
samples the voltage and current thousands of times a second. For each sample, the voltage
is multiplied by the current at the same instant; the average over at least one cycle is the
real power. The real power divided by the apparent volt-amperes (VA) is the power factor.
A computer circuit uses the sampled values to calculate RMS voltage, RMS current, VA,
power (watts), power factor, and kilowatt-hours. The readings may be displayed on the
device, retained to provide a log and calculate averages, or transmitted to other equipment
for further use.
5. VAr meter-: VAr is the unit of reactive power, which is the total power
absorbed by the reactive elements i.e. inductor and capacitor. A VAr meter usually
measures VI*sin(ᶲ) which is the total reactive power in the circuit. For higher values of
reactive power reading of the meter is shown in KVAr or MVAr.
Figure – 3.31 Digital Wattmeter

48. 48
6. Temperature indicator-: It is a microprocessor based digital
temperature indicator used for the temperature indication of the transformer winding and
the transformer oil used for cooling. RTD’s are connected for the temperature measurement
in the transformer, which are connected to the temperature indicator.
7. Alarms and annunciator panel-: An annunciator panel, also known
as the Centralized Warning Panel (CWP), is a group of lights used as a central indicator of
status of equipment or systems in a sub-station, industrial process, building or other
installation. Usually, the annunciator panel includes a main warning lamp or audible signal
to draw the attention of operating personnel to the annunciator panel for abnormal events
Figure – 3.32 Digital Mvar Meter
Figure – 3.33 Temperature Indicator

49. 49
or conditions. It is basically an audio-visual warning system, which highlights the fault
which is going on, or even before it happens. This is very necessary for safety concerns
also, and sometimes warning comes before improper procedure which warns the operator
to avoid unwanted accident etc.
Figure – 3.34 Annunciators for 132/33 KV transformer
Figure – 3.35 Annunciator for 33 KV feeders

50. 50
7.1 Fire alarm annunciator-: In sub-stations, a central fire alarm annunciator
panel is located where it is accessible to fire-fighting crews. The annunciator panel will
indicate the zone and approximate physical location of the source of a fire alarm in the sub-
station. The annunciator will also include lamps and audible warning devices to indicate
failures of alarm circuits. In a sub-station, the fire annunciator may also be associated with
a control panel for ventilation systems, and may also include emergency communication
systems for the station.
8. Lighting control of yard and control room-: Lighting is done in
the whole yard is done for the supervision of the yard at night. The lamps are placed at the
top of the towers so that it can lights up the whole yard. All the yard lighting and substation
accessories are connected with the 33/0.4 KV transformer. For security purpose of all the
substation accessories M.C.B. panels are established inside the control room.
Figure – 3.36 Annunciator for 132 KV line
Figure – 3.37 Fire alarm annunciator for 132/33 KV transformer

51. 51
3.2.3 Controlling-: The operating personnel can control the yard activities from
the control room even if they are not even present physically in the yard. For this purpose,
controlling switches are provided in the panel by which they can open or close a circuit
breaker or an isolator.
Figure – 3.38 Controlling Panel for Sub-Station Requirements
Figure – 3.39 Controlling Switches

52. 52
3.3 PLC room-: PLC stands for Power Line Carrier. For long overhead lines the
power line itself may be used as the interconnecting channel between the terminal
equipments. Carrier-current protection is the most widely used scheme for the protection of
Extra High Voltage (EHV) and Ultra High Voltage (UHV) power lines. The carrier signal
is directly coupled to the power line itself which is to be protected. Carrier-current
protection is faster and superior to distance protection schemes and is more reliable when
used for long transmission lines, although the terminal equipments are more expensive and
complicated. In addition to protection the carrier signals can also be used for
communication, supervisory control and telemetering.
In carrier-current protection, the circuit breakers at both the ends of the line trip
simultaneously when a fault occurs at one of the ends of the protected line sections. This
helps in improving the stability. The carrier signals can be used either to initiate or to
prevent the tripping of a protective relay according to which they are classified. When a
carrier signal is used to initiate tripping of relay, the scheme is known as carrier inter-
tripping, or transfer tripping or permissive tripping scheme. The scheme is known as carrier-
blocking scheme when the carrier signals are used to prevent the operation of a relay. In
this sub-station carrier, current protection is not in much use.
Figure – 3.40 Ratings Of PLC Panel

53. 53
3.3 Battery Room-: Battery room consist of battery panels for the operation of relay
and controlling panels as they all requires D.C. supply for their operation. A battery room
must be designed for proper air ventilation to prevent any explosion.
Figure – 3.41 Batteries

54. 54
3.4.1 Battery panel-: Battery panel has two group of batteries one of 48 V and
one of 110 V. It consists of several batteries connected in series so that they add up to 110
volt or 48 V. These are Ni-Cd batteries, which are rechargeable and also known secondary
batteries. Sulphuric acid is used as an electrolyte in these batteries and it is mixed with
dilute water. Each battery has the same ratings as below:
Voltage=2 Volts Ampere Hours=500 Ah
A battery charger is used for the charging of batteries. Battery charger is nothing but it is
a A.C. to D.C. converter. Two battery chargers are used for 110 V one charger is used as a
backup.
Figure – 3.42 Battery Charger

55. 55
4. NEW TECHNOLOGIES
As the electricity sector is changing continuously new technologies are added to the sub-
station prior to security and measurement.
4.1 Thermo-scanner-: Thermo-scanner is a temperature measurement device
used for measurement of the temperature usually for different types of clamps, because at
point of junction they get overheated, so to get an information about the operating condition
of the clamp thermos-scanner is used.
The first principle of thermal imaging is “many components heat up before they fail.
Second, all objects emit thermal radiation in the infrared spectrum that is not seen by the
human eye.
Third, thermal imaging cameras convert that radiation to crisp images from which
temperatures can be read. This non-contact temperature data can be displayed on a monitor
in real time, and can also be sent to a digital storage device for analysis.
Thermal imaging cameras do not require light to produce images, and can see hot
spots well before excessive heat or loss of insulation leads to failure. They can be mounted
in all-weather housings and placed on pan/tilt drive mechanisms to survey large areas of a
substation. Due to FLIR's wide selection of lenses with different focal lengths. Therefore,
they support 24/7 monitoring in all types of weather and locations.
FLIR thermal imaging cameras recognize differences in the heat signatures of
electrical components and the surrounding background (such as the sky or clouds), and can
compare the temperatures of similar components in close proximity to one another. Built-
in logic, memory, and data communications allow them to compare the temperatures in
their images with user defined settings, and send that data to a central monitoring station
for trend analysis triggering alarms, and generating exception reports. This makes them
ideal for unattended monitoring of substation equipment.
4.2 Nitrogen Fire Controller-: This is used for the protection of transformer of
132/33 KV from dangerous fire hazards. It uses nitrogen for extinguishing the fire from the
transformer.

56. 56
Nitrogen injection system is activated when the collected signals, which are released by gas
relay and fire detector, meet preset requirements. After activation, the pressure relief valve
(oil drain valve) is opened in a short time to discharge some transformer oil so as to reduce
pressure inside, and the shut off valve, which is set between transformer and oil conservator,
is switched off due to sudden flow increase in order to stop oil in the conservator from
flowing into the transformer.
After some delay time, the nitrogen injection fire protection system will
continuously inject nitrogen gas into the transformer to cool down fault point inside the
transformer. As a result, the temperature is reduced to below ignition point, and fire is put
out.
Figure – 3.44 Nitrogen Fire Contrller

57. 57
5. FUTURE EXTENSIONS
The control room and the yard has designed such that two more feeders can installed in the
sub-station for the future increase in the load surrounding the sub-station areas.

58. 58
References: -
 http://www.ptcul.org/cms/details.php?pgID=_about
 http://www.ptcul.org/cms/documents/transmissionmap(Line-
Diagram)_2016.pdf
 http://www.ptcul.org/cms/documents/transmission_map_of_ptcul_201
6.pdf
 Power system Protection and Switchgear by B. Ram and D. N.
Vishwakarma.