NTDC 220kV Transmission gird station Internship report

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INTERNSHIP REPORT
ON
220/132 Kv gird station jamshoro-t.M khan road
Submitted By:
ANEEL KUMAR 14EL97
Department of electrical engineering

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ACKNOWLEDGEMENT
All the praises and admires for our Almighty Allah who enabled me to complete and
write the internship and internship report on National Transmission and Dispatch company.
I want to knowledge to all of those who helped me to complete my report and to gain
knowledge about activities throughout the period of my internship in NTDC.
I want to pay great thanks to NTDC staff in NTDC gird station T.M khan road that
guided me and helped me during my internship over there. Also, I want to thanks to NTDC
for giving me this great opportunity to do internship.

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EXECUTIVE SUMMARY
I joined NTDC gird station at T.M khan road 11/01/2018. My internship report
includes all the information about my internship. The information is collected from both the
sources primary and secondary.
National transmission and dispatch company (NTDC) Limited was incorporated on
6th
November 1998 and commenced commercial operation on 24th
December 1998. It was
organized to take overall the properties, rights and assets obligations and liabilities of 220 KV
and 500 KV Gird station and transmission lines/network owned by Pakistan Water and Power
Development Authority (WAPDA). NTDC operates and maintains twelve 500 KV and
twenty nine 220 KV gird station, 5077 km of 500 KV transmission line and 7359 km of 220
KV transmission line in Pakistan.
NTDC was granted Transmission License No. TL/01/2002 on 31st
December 2002 by
National Electric Power Regularity Authority (NEPRA) to engage in the exclusive
transmission business from a term of thirty years, pursuant to section 17 of regulation of
generation, transmission and distribution of electric power act 1997.
Grid station regulates and controls the power between this voltage to some low levels
and supplied electric power to the sub stations or to other grid stations at the same voltage
level according to the requirements interconnected transmission lines to increase the
reliability of the power system. It receives power from the power station at extremely high
voltage and then convert.

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TABLES OF CONTEXT
Unit No: 1
Gird station and Sub-station --------------------------------------------------------05
Unit No: 2
One line Diagram and Bus Bar ----------------------------------------------------08
Unit No: 3
Switches ------------------------------------------------------------------------------13
Unit No: 4
Relay Switch -------------------------------------------------------------------------19
Unit No: 5
Transformer ------------------------------------------------------- -------------------21
Unit No: 6
Battery Room -------------------------------------------------------------------------25
Unit No: 7
Relay Room & Control Room &Protective device -------------------- ---------28
Unit No: 8
Equipment’s Maintenance ----------------------------------------------------------31

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UNIT NO: 1 GIRD STATION AND SUB-STATION
An electrical power substation is a conversion point between transmission level
voltages (such as 132Kv) and distribution level voltages (such as 11Kv). A substation has one
or more step-down transformers and serves a regional area such as part of a city or
neighborhood. Substations are connected to each other by the transmission ring circuit system
by equipment’s.
An electrical grid station is an interconnection point between two transmission ring
circuits, often between two geographic regions. They might have a transformer, depending on
the possibly different voltages, so that the voltage levels can be adjusted as needed.
The interconnected network of sub stations is called the grid, and may ultimately
represent an entire multi-state region. In this configuration, loss of a small section, such as
loss of a power station, does not impact the grid as a whole, nor does it impact the more
localized neighborhoods, as the grid simply shifts its power flow to compensate, giving the
power station operator the opportunity to affect repairs without having a blackout.
DEFINITION OF SUB-STATION:
The assembly of apparatus used to change some characteristics (e.g. Voltage level,
frequency, power factor etc.) of electric supply is called sub-station”.
CLASSIFICATION OF SUB-STATION:
There are several ways of classifying sub-station. However the two most important way
of classifying they are:
I. According to service requirement
II. According to service requirement sub-station may be classified into:
1) ACCORDING TO SERVICE REQUIREMENT
a. TRANSFORMER SUB-STATION:
Those sub-station which change the voltage levels of electrical supply are
called TIF s/s.
b. SWITCHING SUB-STATION:
This sub-station simply performs the switching operation of power line.
c. POWER FACTOR CORRECTION S/S:
These sub-station which improve the power factor of the system are called power
factor correction s/s. these are generally located at receiving end s/s.
d. FREQUENCY CHANGER S/S:
Those sub-stations, which change the supply frequency, are known as frequency
changer s/s. Such s/s may be required for industrial utilization.

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e. CONVERTING SUB-STATION:
That sub-station which change AC power into DC power are called converting s/s
ignition is used to convert AC to dc power for traction, electroplating, electrical welding
etc.
f. INDUSTRIAL SUB-STATION:
Those sub-stations, which supply power to individual industrial concerns, are
known as industrial sub-station.
2) ACCORDING TO CONSTRUCTIONAL FEATURE
According to constructional features, the sub-station are classified as
a) OUTDOOR SUB-STATION:
For voltage beyond 66KV, equipment is invariably installed outdoor. It is because
for such Voltage the clearances between conductor and the space required for switches ,
CB and other equipment becomes so great that it is not economical to install the
equipment becomes so great that it is not economical to install the equipment indoor.
b) INDOOR SUB-STATION:
For voltage up to 11KV, the equipment of the s/s is installed indoor because of
economics consideration. However when the atmosphere is contaminated with impurities,
these sub-station can be erected for voltage up to 66 KV.
c) UNDERGROUND SUB-STATION:
In thickly populated areas, the space available for equipment and building is
limited and the cost the land is high. Under such situation the sub-station is created
underground.
FUNCTION OF GIRD STATION
 Supply required electrical power
 Maximum possible coverage of the supply network
 Maximum security of supply
 Shortest possible fault duration
 Optimum efficiency of plant and the network
 Supply of electrical power within targeted frequency limit
 Supply of electrical power within specified voltage limits
 Supply of electrical energy to the consumers at the lowest cost
An important function performed by a gird station switching, that is the connecting and
disconnecting of transmission lines or other components to and from the system. Switching
events may be "planned “or "unplanned”. A transmission line or other component may need
to be de energized for maintenance or for new construction; for example, adding or removing
a transmission line or a transformer. To maintain reliability of supply, no company ever
brings down its whole system for maintenance. All work to be performed, from routine
testing to adding entirely new substations, must be done while keeping the whole system

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running. Perhaps more importantly, a fault may develop in a transmission line or any other
component. Some examples of this: a line is hit by lightning and develops an arc, or a tower
is blown down by a high wind. The function of the grid station is to isolate the faulted portion
of the system in the shortest possible time.
ADVANTAGES OF THE GRID SYSTEM:
 Any time electricity is available for the consumers at lower cost.
 Flow of electrical energy is continuous and sure.
 It is possible to fulfill the emergency demand of power.
 Better regulation of the voltages.
 Improved power factor
 It is possible to govern the generator according to the load.
 Keep Safe transmission system.
 Reduced fault timings.
 Control frequency range.
DISADVANTAGES OF THE GRID SYSTEM
 Cost of the control system is increased and their maintenance is complicated.
 Power system is affected from the environmental factors.
 This system is unsafe during the war.
 Extended system is going to complexity.
 Due to the expensive equipment’s, additional load occurred on the consumers.
 During short circuit condition it is impossible to maintain the continuity of power.
 High initial and maintenance cost.
 During load shedding, capacity of industries connected with the grid is reduced which
cause to industrial development problem.
 For maintenance, qualified staff is required and for that reason our country has to
spend more money to call expert engineers from other countries.

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UNIT NO: 2 ONE LINE DIAGRAM AND BUS BAR
ONE LINE DIAGRAM:
Single line or one-line diagram is a drawing that shows by single lines and symbols a
simplified layout of a three-phase electrical system. It get their name form the fact only one
phase of three phase system is shown and only one line is used to represent any number of
current carrying conductors. Standard symbols are used to represent components of power
systems such as transformers, circuit breakers, isolator, generators, fuses and switches.
An up-to-date single-line diagram is vital for a variety of service activities including:
• Short circuit calculations
• Coordination studies
• Load flow studies
• Safety evaluation studies
• All other engineering studies
• Electrical safety procedures
• Efficient maintenance
BENEFITS:
• Help identify fault locations and simplifies troubleshooting
• Identify potential sources of electric energy during LOTO procedure
• Ensure safety of personnel
• Stay compliant with gird requirements
• Ensure safe, reliable operation of facility
SCOPE
To give you an accurate picture of your electrical system, the single-line diagram
information normally includes:
• Incoming lines (voltage and size)
• Incoming main fuses, potheads, cutouts, switches and main/tie breakers
• Power transformers (rating, winding connection and grounding means)
• Feeder breakers and fused switches
• Relays (function, use and type)
• Current/potential transformers (size, type and ratio)
• Control transformers
• All main cable and wire runs with their associated isolating switches and potheads
(size and length of run)
• All substations, including integral relays and main panels and the exact nature of the
load in each feeder and on each substation

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SINGLE LINE DIAGRAM OF 220/132 KV GIRD STATION T.M KHAN ROAD HYDERABAD

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BUS BAR:
In electric power distribution, a bus bar (also bus bar, buss bar or buss bar) is a
metallic strip or bar, typically housed inside switchgear, panel boards, and bus way
enclosures for local high current power distribution. They are also used to connect high
voltage equipment at electrical switchyards, and low voltage equipment in battery banks.
They are generally UN insulated, and have sufficient stiffness to be supported in air by
insulated pillars. These features allow sufficient cooling of the conductors, and the ability to
tap in at various points without creating a new joint.
DESIGN AND PLACEMENT:
The material composition and cross-sectional size of the bus bar determine the
maximum amount of current that can be safely carried. Bus bars can have a cross-sectional
area of as little as 10 square millimeters, but electrical substations may use metal tubes 50
millimeters in diameter (20 square millimeters or more as bus bars. An aluminum smelter
will have very large bus bars used to carry tens of thousands of amperes to the
electrochemical cells that produce aluminum from molten salts.
Bus bars are produced in a variety of shapes such as flat strips, solid bars and rods
typically copper, brass or aluminum in solid or hollow tubes. Some of these shapes allow heat
to dissipate more efficiently due to their high surface area to cross-sectional area ratio. The
skin effect makes 50–60 Hz AC bus bars more than about 8 millimeters thickness inefficient,
so hollow or flat shapes are prevalent in higher current applications. A hollow section also
has higher stiffness than a solid rod of equivalent current-carrying capacity, which allows a
greater span between bus bar supports in outdoor electrical switchyards.
A bus bar must be sufficiently rigid to support its own weight, and forces imposed by
mechanical vibration and possibly earthquakes, as well as accumulated precipitation in
outdoor exposures. In addition, thermal expansion from temperature changes induced by ohm
heating and ambient temperature variations, and magnetic forces induced by large currents
must be considered.
Distribution boards split the electrical supply into separate circuits at one location.
Bus ways, or bus ducts, are long bus bars with a protective cover. Rather than branching from
the main supply at one location, they allow new circuits to branch off anywhere along the
route of the bus way.
A bus bar may either be supported on insulators, or else insulation may completely
surround it. Bus bars are protected from accidental contact either by a metal earthed
enclosure or by elevation out of normal reach. Power neutral bus bars may also be insulated
because it is not guaranteed that the potential between power neutral and safety grounding is
always zero. Earthing (safety grounding) bus bars are typically bare and bolted directly onto
any metal chassis of their enclosure. Bus bars may be enclosed in a metal housing, in the
form of bus duct or bus way, segregated-phase bus, or isolated-phase bus.
 The bus bar arrangement is simple and easy in maintenance.
 It must have the provision of extension with the load growth.
 The installation should be as economical as possible, keeping in views the needs and
continuity of supply.
 There is the availability of alternative arrangements in the in the event of the outage
of any of the apparatus.

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BUS SCHEMES:
A substation bus scheme is the arrangement of overhead bus bar and associated
switching equipment (circuit breakers and isolators) in a substation. The operational
flexibility and reliability of the substation greatly depends upon the bus scheme.
The first requirement of any substation design is to avoid a total shutdown of the substation
for the purpose of maintenance, or due to fault somewhere out on the line. A total shutdown
of the substation means complete shutdown of all the lines connected to the substation.
Clearly, a high transmission substation where a large number of critical lines terminate is
extremely important, and the substation should be designed to avoid total failure and
interruption of minimum numbers of circuits.
1. Simplicity of system.
2. Easy maintenance of different equipment’s.
3. Minimizing the outage during maintenance.
4. Future provision of extension with growth of demand.
5. Optimizing the selection of bus bar arrangement scheme so that it gives maximum
return from the system.
There are six different schemes.
1. Single bus single breaker scheme
2. Main and transfer bus scheme
3. Double bus single breaker scheme
4. Double bus double breaker scheme
5. Ring bus scheme
6. Double bus one and half breaker scheme
Among these six scheme in T.M khan grid station using “Double Bus one and half Breaker
scheme”
So I am going to define it.
DOUBLE BUS ONE AND HALF BREAKER SCHEME
This is an improvement on the double breaker scheme to effect saving in the number
of circuit breakers. For every two circuits only one spare breaker is provided. The protection
is however complicated since it must associate the central breaker with the feeder whose own
breaker is taken out for maintenance. As shown in the figure that it is a simple design, two
feeders are fed from two different buses through their associated breakers and these two
feeders are coupled by a third breaker which is called tie breaker. Normally all the three
breakers are closed and power is fed to both the circuits from two buses which are operated in
parallel. The tie breaker acts as coupler for the two feeder circuits.
During failure of any feeder breaker, the power is fed through the breaker of the
second feeder and tie breaker, therefore each feeder breaker has to be rated to feed both the
feeders, coupled by tie breaker. In this bus configuration, three breakers are required for
every two circuits - hence the "one and half" name. Think of it as, to control one circuit
requires one full and a half breaker. The middle breaker is shared by both circuits, similar to a
ring bus scheme where each circuit is fed from both sides. Any circuit breaker can be isolated

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and removed for maintenance purposes without interrupting supply to any of the other
circuits. Additionally, one of the two main busses can be removed for maintenance without
interruption of service to any of the other circuits.
If a middle circuit breaker fails, the adjacent breakers are also tripped to interrupt both
circuits. If a breaker adjacent to the bus fails, tripping of the middle breaker will not interrupt
service to the circuit associated with the remaining breaker in the chain. Only the circuit
associated with the failed breaker is removed from service.
ADVANTAGES OF ONE AND A HALF BREAKER BUS SYSTEM
During any fault on any one of the buses, that faulty bus will be cleared instantly
without interrupting any feeders in the system since all feeders will continue to feed from
other healthy bus.
It is very flexible, highly reliable, and more economical in comparison to the Double Bus
Double Breaker scheme. Protective relay schemes in this configuration are highly
complicated as the middle breaker is associated with two circuits. It also requires more space
in comparison to other schemes in order to accommodate the large number of components.
ONE AND HALF SCHEME SIMPLE DIAGRAM

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UNIT NO: 3 SWITCHES
An electrical switch is any device used to interrupt the flow of electrons in a circuit.
Switches are essentially binary devices: they are either completely on (“closed”) or
completely off (“open”). The simplest type of switch is one where two electrical conductors
are brought in contact with each other by the motion of an actuating mechanism. There are
two types of switches,
1) Mechanical or electromechanical switches
2) Electronic switches
MECHANICAL OR ELECTROMECHANICAL SWITCHES:
These switches must be activated physically, by moving, pressing, releasing, or
touching its contacts.
Mechanical switches can be classified into different types based on several factors
such as method of actuation, number of contacts, operation and construction, based on state,
etc.
ELECTRONICS SWITCHES:
Electronic switches do not require any physical contact in order to control a circuit.
These are activated by semiconductor action.
The electronic switches are generally called as solid state switches because there are
no physical moving parts and hence absence of physical contacts. Most of the appliances are
controlled by semiconductor switches such as motor drives and HVAC equipment’s. There
are different types of solid state switches are available include transistors, SCRs, MOSFETs,
TRIACs and IGBTs.
DIFFERENT TYPES OF SWITCHES USING IN GRID STATION
 Circuit Breaker
 Isolator
CIRCUIT BREAKER:
Electrical circuit breaker is a switching device which can be operated manually and
automatically for controlling and protection of electrical power system respectively. As the
modern power system deals with huge currents, the special attention should be given during
designing of circuit breaker for safe interruption of arc produced during the operation of
circuit breaker. The modern power system deals with huge power network and huge numbers
of associated electrical equipment’s. During short circuit fault or any other types of electrical
fault these equipment as well as the power network suffer a high stress of fault current in
them which may damage the equipment and networks permanently.
For timely disconnecting and reconnecting different parts of power system network
for protection and control, there must be some special type of switching devices which can be

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operated safely under huge current carrying condition. During interruption of huge current,
there would be large arcing in between switching contacts, so care should be taken to quench
these arcs in circuit breaker in safe manner. The circuit breaker is the special device which
does all the required switching operations during current carrying condition.
WORKING PRINCIPLE OF CIRCUIT BREAKER
The circuit breaker mainly consists of fixed contacts and moving contacts. In normal
"ON" condition of circuit breaker, these two contacts are physically connected to each other
due to applied mechanical pressure on the moving contacts. There is an arrangement stored
potential energy in the operating mechanism of circuit breaker which is released if switching
signal is given to the breaker. The potential energy can be stored in the circuit breaker by
different ways like by deforming metal spring, by compressed air, or by hydraulic pressure.
But whatever the source of potential energy, it must be released during operation. Release of
potential energy makes sliding of the moving contact at extremely fast manner. All circuit
breaker have operating coils (tripping coils and close coil), whenever these coils are
energized by switching pulse, and the plunger inside them displaced. This operating coil
plunger is typically attached to the operating mechanism of circuit breaker, as a result the
mechanically stored potential energy in the breaker mechanism is released in forms of kinetic
energy, which makes the moving contact to move as these moving contacts mechanically
attached through a gear lever arrangement with the operating mechanism. After a cycle of
operation of circuit breaker the total stored energy is released and hence the potential energy
again stored in the operating mechanism of circuit breaker by means of spring charging motor
or air compressor or by any other means. The circuit breaker has to carry large rated or fault
power. Due to this large power there is always dangerously high arcing between moving
contacts and fixed contact during operation of circuit breaker. Again as we discussed earlier
the arc in circuit breaker can be quenching safely if the dielectric strength between the current
carrying contacts of circuit breaker increases rapidly during every current zero crossing of the
alternating current. The dielectric strength of the media in between contacts can be increased
in numbers of ways, like by compressing the ionized arcing media since compressing
accelerates the deionization process of the media, by cooling the arcing media since cooling
increase the resistance of arcing path or by replacing the ionized arcing media by fresh
gasses. Hence a numbers of arc quenching processes should be involved in operation of
circuit breaker.
TYPES OF CIRCUIT BREAKER
According different criteria there are different types of circuit breaker. According to their arc
quenching media the circuit breaker can be divided as-
ACCORDING TO THEIR ARC QUENCHING MEDIA THE CIRCUIT BREAKER CAN BE DIVIDED
AS
1. Oil circuit breaker
2. Air circuit breaker
3. SF6 circuit breaker
4. Vacuum circuit breaker
ACCORDING TO THEIR SERVICES THE CIRCUIT BREAKER CAN BE DIVIDED AS-

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1. Outdoor circuit breaker
2. Indoor breaker.
ACCORDING TO THE OPERATING MECHANISM OF CIRCUIT BREAKER THEY CAN BE
DIVIDED AS-
1. Spring operated circuit breaker
2. Pneumatic circuit breaker
3. Hydraulic circuit breaker
ACCORDING TO THE VOLTAGE LEVEL OF INSTALLATION TYPES OF CIRCUIT BREAKER
ARE REFERRED AS
1. High voltage circuit breaker
2. Medium voltage circuit breaker
3. Low voltage circuit breaker
HIGH VOLTAGE SF6 SPRING OPERATED CIRCUIT BREAKER
A circuit breaker in which the current carrying contacts operate in Sulphur
hexafluoride or SF6 gas is known as an SF6 circuit breaker.
SF6 has excellent insulating property. SF6 has high electro-negativity. That means it has high
affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas
molecule, it is absorbed by that gas molecule and forms a negative ion.
The attachment of electron with SF6 gas molecules may occur in two different ways, These
negative ions obviously much heavier than a free electron and therefore over all mobility of
the charged particle in the SF6 gas is much less as compared to other common gases. We
know that mobility of charged particle is majorly responsible for conducting current through
a gas.
Hence, for heavier and less mobile charged
particles in SF6 gas, it acquires very high dielectric
strength he gas has a good dielectric strength but
also it has the unique property of fast
recombination after the source energizing the spark
is removed. The gas has also very good heat
transfer property. Due to its low gaseous viscosity
(because of less molecular mobility) SF6 gas can
efficiently transfer heat by convection. So due to its
high dielectric strength and high cooling effect SF6
gas is approximately 100 times more effective arc
quenching media than air. Due to these unique

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properties of this gas, SF6 circuit breaker is used in complete range of medium voltage and
high voltage electrical power system. These circuit breakers are available for the voltage
ranges from 33KV to 800 KV and even more.
TYPES OF SF6 CIRCUIT BREAKER
There are mainly three types of SF6 CB depending upon the voltage level of application-
1. Single interrupter SF6 CB applied for up to 245 KV (220 KV) system.
2. Two interrupter SF6 CB applied for up to 420 KV (400 KV) system.
3. Four interrupter SF6 CB applied for up to 800 KV (715 KV) system.
WORKING OF SF6 CIRCUIT BREAKER
The working of SF6 CB of first generation was quite simple and it is some extent
similar to air blast circuit breaker. Here SF6 gas was compressed and stored in a high pressure
reservoir. During operation of SF6 circuit breaker this highly compressed gas is released
through the arc in breaker and collected to relatively low pressure reservoir and then it is
pumped back to the high pressure reservoir for re utilize. The working of SF6 circuit breaker
is little bit different in modern time. Innovation of puffer type design makes operation of SF6
CB much easier. In buffer type design, the arc energy is utilized to develop pressure in the
arcing chamber for arc quenching.
Here the breaker is filled with SF6 gas at rated pressure. There are two fixed contact
fitted with a specific contact gap. A sliding cylinder bridges these to fixed contacts. The
cylinder can axially slide upward and downward along the contacts. There is one stationary
piston inside the cylinder which is fixed with other stationary parts of the SF6 circuit breaker,

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in such a way that it cannot change its position during the movement of the cylinder. As the
piston is fixed and cylinder is movable or sliding, the internal volume of the cylinder changes
when the cylinder slides.
During opening of the breaker the cylinder moves downwards against position of the fixed
piston hence the volume inside the cylinder is reduced which produces compressed SF6 gas
inside the cylinder. The cylinder has numbers of side vents which were blocked by upper
fixed contact body during closed position. As the cylinder move further downwards, these
vent openings cross the upper fixed contact, and become unblocked and then compressed SF6
gas inside the cylinder will come out through this vents in high speed towards the arc and
passes through the axial hole of the both fixed contacts. The arc is quenched during this flow
of SF6 gas.
During closing of the circuit breaker, the sliding cylinder moves upwards and as the position
of piston remains at fixed height, the volume of the cylinder increases which introduces low
pressure inside the cylinder compared to the surrounding. Due to this pressure difference SF6
gas from surrounding will try to enter in the cylinder. The higher pressure gas will come
through the axial hole of both fixed contact and enters into cylinder via vent and during this
flow; the gas will quench the arc.
ISOLATOR
Circuit breaker always trip the circuit but open contacts of breaker cannot be visible
physically from outside of the breaker and that is why it is recommended not to touch any
electrical circuit just by switching off the circuit breaker. So for better safety there must be
some arrangement so that one can see open condition of the section of the circuit before
touching it. Isolator is a mechanical switch which isolates a part of circuit from system as
when required. Electrical isolators separate a part of the system from rest for safe
maintenance works.
So definition of isolator can be rewritten as Isolator is a manually operated mechanical switch
which separates a part of the electrical power. Isolators are used to open a circuit under no
load. Its main purpose is to isolate one portion of the circuit from the other and is not
intended to be opened while current is flowing in the line. Isolators are generally used on
both ends of the breaker in order that repair or replacement of circuit breaker can be done
without and danger.
TYPES OF ELECTRICAL ISOLATORS
There are different types of isolators available depending upon system requirement such
as
1. Double Break Isolator
2. Single Break Isolator
3. Pantograph type Isolator.
Depending upon the position in power system, the isolators can be categorized as
1. Bus side isolator – the isolator is directly connected with main bus

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2. Line side isolator – the isolator is situated at line side of any feeder
3. Transfer bus side isolator – the isolator is directly connected with transfer bus.
AUTO RECLOSER
Auto Recloser, is a circuit breaker equipped with a mechanism that can automatically
close the breaker after it has been opened due to a fault. Reclosers are used on overhead
distribution systems to detect and interrupt momentary faults. Since many short-circuits
on overhead lines clear themselves, a recloser improves service continuity by automatically
restoring power to the line after a momentary fault.
Most of the faults on overhead lines are transient in nature. About 85% to 90% of faults are
momentary and caused by tree branches, lightning, birds etc. These conditions results in
arcing faults which lasts for very small duration and clears after that moment. The arc
generated can be extinguished and the line can be reenergized. For this momentary faults
which recovers on its own normal circuit breaker operation of opening the faulty part is not
advisable. Some provision should be permitted in circuit breakers to close the breaker
contacts if the fault is cleared momentarily. This fact is employed as a basis for auto-
reclosers.

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UNIT NO: 4 RELAY SWITCH
A relay is an electrically operated switch. Many relays use an electromagnet to
mechanically operate a switch, but other operating principles are also used, such as solid-state
relays. Relays are used where it is necessary to control a circuit by a separate low-power
signal, or where several circuits must be controlled by one signal.
TYPES OF ELECTRICAL PROTECTION RELAYS
 Over Current Relay
 Differential Relay
 Thermal Relay
 Distance Relay
 OVER CURRENT RELAY
In an over current relay or o/c relay the actuating quantity is only current. There is only one
current operated element in the relay, no voltage coil etc. are required to construct
this protective relay.
 DIFFERENTIAL RELAY
The differential relay is one that operates when there is a difference between two or more
similar electrical quantities exceeds a predetermined value. In differential relay scheme
circuit, there are two currents come from two parts of an electrical power circuit.
 THERMAL RELAY
The coefficient of expansion is one of the basis properties of any material. Two different
metals always have different degree of linear expansion. A bimetallic strip always bends
when it heated up, due to this inequality of linear expansion of two different metals.

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 DISTANCE OR IMPEDANCE RELAY
There is one type of relay which functions depending upon the distance of fault in the line.
More specifically, the relay operates depending upon the impedance between the point of
fault and the point where relay is installed. These relays are known as distance
relay or impedance relay.

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UNIT NO: 5 TRANSFORMER
Transformer is a device which transfer the electrical power from one level to another
level. It means by changing voltage and current. But, power and frequency remain same.
TYPES OF TRANSFORMER
 Power transformer
 Auto transformer
 Instrument transformer
POWER TRANSFORMER:
Electrical transformer is a static device which transforms electrical energy from one circuit to
another without any direct electrical connection and with the help of mutual induction
between two windings. It transforms power from one circuit to another without changing its
frequency but may be in different voltage level. In this gird two power transformer 10/13
MVA 132/11 KV are used.
USE OF POWER TRANSFORMER
Generation of electrical power in low voltage level is very much cost effective. Theoretically,
this low voltage level power can be transmitted to the receiving end. This low voltage power
if transmitted results in greater line current which indeed causes more line losses But if the
voltage level of a power is increased, the current of the power is reduced which causes
reduction in I2
R losses in the system, reduction in cross sectional area of the conductor i.e.
reduction in capital cost of the system and it also improves the voltage regulation of the
system. Because of these, low level power must be stepped up for efficient electrical power
transmission. This is done by step up transformer at the sending side of the power system
network. As this high voltage power may not be distributed to the consumers directly, this
must be stepped down to the desired level at the receiving end with the help of step down
transformer. Electrical power transformer thus plays a vital role in power transmission. Two
winding transformers are generally used where ratio of high voltage and low voltage is
greater than 2. It is cost effective to use auto transformer where the ratio between high
voltage and low voltage is less than 2. Again a single unit three phase transformer is more
cost effective than a bank of three single phase transformers unit in a three phase system.
AUTO TRANSFORMER:
Auto transformer is kind of electrical transformer where primary and secondary shares same
common single winding. So basically it’s a one winding transformer. In Auto Transformer,
one single winding is used as primary winding as well as secondary winding. Auto
transformer where the ratio between high voltage and low voltage is less than 2. In this grid
two auto transformer of 132/160 MVA 220/132 KV are used and connected in parallel with
each other.

22
ADVANTAGES OF USING AUTO TRANSFORMERS
1. For transformation ratio = 2, the size of the auto transformer would be approximately 50%
of the corresponding size of two winding transformer. For transformation ratio say 20
however the size would be 95 %. The saving in cost of the material is of course not in the
same proportion. The saving of cost is appreciable when the ratio of transformer is low,
that is lower than 2. Thus auto transformer is smaller in size and cheaper.
2. An auto transformer has higher efficiency than two winding transformer. This is because
of less Resistive loss and core loss due to reduction of transformer material.
3. Auto transformer has better voltage regulation as voltage drop in resistance and reactance
of the single winding is less.
Disadvantages of Using Auto Transformer
1. Because of electrical conductivity of the primary and secondary windings the lower
voltage circuit is liable to be impressed upon by higher voltage. To avoid breakdown in
the lower voltage circuit, it becomes necessary to design the low voltage circuit to
withstand higher voltage.
2. The leakage flux between the primary and secondary windings is small and hence the
impedance is low. This results into severer short circuit currents under fault conditions.
3. The connections on primary and secondary sides have necessarily needs to be same,
except when using interconnected starring connections. This introduces complications due
to changing primary and secondary phase angle particularly in the case of delta/delta
connection.
4. Because of common neutral in a star/star connected auto transformer it is not possible to
earth neutral of one side only. Both their sides should have their neutrality either earth or
isolated.
5. It is more difficult to maintain the electromagnetic balance of the winding when voltage
adjustment tapings are provided. It should be known that the provision of tapping on an
auto transformer increases considerably the frame size of the transformer. If the range of
tapping is very large, the advantages gained in initial cost is lost to a great event.
Instrument Transformers
Instrument Transformers are used in AC system for measurement of electrical quantities
i.e. voltage, current, power, energy, power factor, frequency. Instrument transformers are also
used with protective relays for protection of power system.
Basic function of Instrument transformers is to step down the AC System voltage and current.
The voltage and current level of power system is very high. It is very difficult and costly to
design the measuring instruments for measurement of such high level voltage and current.
Generally measuring instruments are designed for 5 A and 110 V. The measurement of such
very large electrical quantities, can be made possible by using the Instrument transformers
with these small rating measuring instruments. Therefore these instrument transformers are
very popular in modern power system.

23
TYPES OF INSTRUMENT TRANSFORMERS
Instrument transformers are of two types –
1. Current Transformer (C.T.)
2. Potential Transformer (P.T.)
CURRENT TRANSFORMER (C.T.)
Current transformer is used to step down the current of power system to a lower level to
make it feasible to be measured by small rating Ammeter (i.e. 5A ammeter).
Primary of C.T. is having very few turns. Sometimes bar primary is also used. Primary is
connected in series with the power circuit. Therefore, sometimes it also called series
transformer. The secondary is having
large no. of turns. Secondary is connected
directly to an ammeter. As the ammeter is
having very small resistance. Hence, the
secondary of current transformer operates
almost in short circuited condition. One
terminal of secondary is earthed to avoid
the large voltage on secondary with
respect to earth. Which in turns reduce
the chances of insulation breakdown and
also protect the operator against high
voltage.
POTENTIAL TRANSFORMER (P.T.)
Potential transformer is used to
step down the voltage of power system to
a lower level to make is feasible to be

24
measured by small rating voltmeter i.e. 110 – 120 V voltmeter.
Primary of P.T. is having large no. of turns. Primary is connected across the line (generally
between on line and earth). Hence, sometimes it is also called the parallel transformer.
Secondary of P.T. is having few turns and connected directly to a voltmeter. As the voltmeter
is having large resistance. Hence the secondary of a P.T. operates almost in open circuited
condition. One terminal of secondary of P.T. is earthed to maintain the secondary voltage
with respect to earth.
PARTS OF TRANSFORMER
a. Primary winding,
b. Secondary winding
c. Buchholz Relay
d. Air vent
e. Breather
f. Oil
g. Radiator
h. HT & LT bushing
i. Tap changer
j. Silica gel
k. Winding temperature gauge
l. Oil temperature gauge
m. CONSERVATOR.
n. DOUBLE DIAPHRAGM EXPLOSION VENT
o. OIL LEVEL INDICATOR
p. Winding temperature indicator
q. RADIATORS

25
UNIT NO: 6 BATTERY ROOM
BATTERY
A battery is a device that converts the chemical energy contained in its active
materials directly into electric energy by means of an electrochemical oxidation-reduction
(redox) reaction. In the case of a rechargeable system, the battery is recharged by a reversal
of the process. This type of reaction involves the transfer of electrons from one material to
another through an electric circuit. In a no electrochemical redox reaction, such as rusting or
burning, the transfer of electrons occurs directly and only heat is involved. As the battery
electrochemically converts chemical energy into electric energy, it is not subject, as are
combustion or heat engines, to the limitations of the Carnot cycle dictated by the second
law of thermodynamics. Batteries, therefore, are capable of having higher energy
conversion efficiencies. Electrochemical operation of a cell (discharge). The discharge
reaction can be written, assuming a metal as the anode material and a cathode material such
as chlorine (Cl2), as follows:
Negative electrode: Anodic reaction (oxidation, loss of electrons)
Zn → Zn2_ _ 2
Positive electrode: Cathodic reaction (reduction, gain of electrons)
Cl _ 2e→ 2Cl_ 2
Overall reaction (discharge): Zn _ Cl → Zn2_ _ 2Cl_ (ZnCl) 2
CHARGE:
During the recharge of a rechargeable or storage cell, the current flow is reversed and
oxidation takes place at the positive electrode and reduction at the negative electrode. As
the anode is, by definition, the electrode at which oxidation occurs and the cathode the one
where reduction takes place, the positive electrode is now the anode and the negative the
cathode. In the example of the Zn/Cl2 cell, the reaction on charge can be written as follows:
Negative electrode: cathodic reaction (reduction, gain of electrons)
Zn2_ _ 2e→ Zn
Positive electrode: anodic reaction (oxidation, loss of electrons)
2Cl_ → Cl _ 2e2
Overall reaction (charge): Zn2_ _ 2Cl_ → Zn _ Cl2
BATTERIES ROOM:
Batteries are very important part of the grid. It works as standby storage device that
provides D.C power to the grid’s dc supply equipment in case of failure of A.C supply.
Different protection devices i.e. relays, circuit breakers and other control equipment of relay

26
room, 11KVcontrol room, 132KV control room and yard operates on 110 D.C volt supply
that is normally supplied by a rectifier. In case of failure of A.C power batteries works as a
standby source of 110 D.C
In this grid station almost on all the 132 kV & 220 kV Sub-stations one set of 220 V, two
sets of 110 V (for protection) and one set of 48 V (for carrier communication) lead Acid
station batteries along with battery chargers are installed. The battery charging equipment’s
comprises of a float charger and a boost charger. Stabilization output voltage is provided in
the float charger to float the battery at the correct level. The battery can be boost charging
after a prolonged mains failure by the boost charger. These chargers have been provided
protection for under voltage DC & earth fault. DC Board is installed to feed various
essential DC load from a separate feeder.
Recommended specific gravity of cells at 270
C (electrolyte temp) should be 1.210 +- 0.005.
Actual temp should be measured in the electrolyte of the cell. If the temp is different than
270
C the correction +- 0.0007/0
C change in temp. Should be made in sp. gr. (Subtract for
temp. below 270
C and add for temp. above 270
C).
Voltage of each cell (float charger in 'ON' position) should be.2.16-2.2 volts.
Volt across 55 cell (110 V) should be maintained between 118.8-121 volts.
Volt across 24 cells (48 V) should be maintained between 51.8-52.8 volts.
Top up cells to the correct level (red mark of float indicator of cell) with pure distilled water
only.
Check for corrosion of connectors and if present remove with fresh water pure distilled
water only.
Check for any lose connection, wipe out old petroleum jelly and apply new jelly.
Carry out boost charging of battery when the sp gr. falls below 1.200, charging current 10%
of the AH capacity and on free gassing reduce current to 50% of the charging current till :-
SPECIFIC GRAVITY
The lead acid battery used in today's automobile is made of plates lead and lead oxide,
in a solution of electrolyte. This solution consists of 65% water and 35% sulfuric acid. The
specific gravity or weight of this solution increases as the battery charges and decreases as
the battery discharges. As the battery discharges, sulfur moves away from the solution and
toward the plates. The opposite is true as the battery is charged, the sulfur returns to the
electrolyte solution. The specific gravity of the electrolyte depends on this 65% to 35% ratio
for the necessary chemical reaction to take place. This ratio is affected by the amount of
sulfuric acid and the temperature of the solution. As the temperature drops, the electrolyte
contracts increasing the specific gravity. As the temperature increases the electrolyte expands
deviating from its optimal ratio and affecting the specific gravity reading. A battery's specific

27
gravity is a great way of measuring a battery's state of charge. This is because during a
discharge, the specific gravity decreases linear with ampere-hours discharged. The specific
gravity also increases as the battery is recharged. A hydrometer is used to measure the
specific gravity of the electrolyte solution in each cell. It's a tool used to measure the density
or weight of a liquid compared to the density of an equal amount of water. A lead acid battery
cell is fully charged with a specific gravity of 1.265 at 80° F. For temperature adjustments,
get a specific gravity reading and adjust to temperature by adding .004 for every 10° F above
80° F and subtracting .004 for every 10° F below 80° F.

28
UNIT NO: 7 RELAY ROOM & CONTROL ROOM &PROTECTIVE DEVICE
RELAY ROOM & CONTROL ROOM
A relay is an electrically operated switch, which is used in one form or another in a
variety of electric operations today. Relays deal with electric signals, which are amplified,
isolated and even repeated.
Similarly, we receive messages and amplify the core message, isolating the problems and
solving them, and repeatedly emphasize key messages. Our medium is design, but we’re very
much in the field of communication.
A control room, operations center, or operations control center (OCC) is a room serving as a
central space where a large physical facility or physically dispersed service can be monitored
and controlled. A control room will often be part of a larger command center.
PORTABLE RELAY ROOMS MAY TYPICALLY CONSIST OF:
 A protection and local control scheme custom-designed for the power system application
 A SCADA RTU fully integrated with the protection scheme for remote monitoring and
control
 Heating, lighting, power supply and air-conditioning to ensure the plant and operating
personnel experience optimal conditions
 A central marshalling box and cable gland plate for ease of external connections.
SURGE ARRESTER
A surge arrester is a device to protect electrical equipment from over-voltage
transients caused by external (lightning) or internal (switching) events. Also called a surge
protection device (SPD) or transient voltage surge suppressor (TVSS), this class of device is
used to protect equipment in power transmission and distribution systems. The energy
criterion for various insulation material can be compared by impulse ratio, the surge arrester
should have a low impulse ratio, so that a surge incident on the surge arrester may be
bypassed to the ground instead of passing through the apparatus.
To protect a unit of equipment from transients occurring on an attached conductor, a surge
arrester is connected to the conductor just before it enters the equipment. The surge arrester is
also connected to ground and functions by routing energy from an over-voltage transient to
ground if one occurs, while isolating the conductor from ground at normal operating voltages.
This is usually achieved through use of a varistor, which has substantially different
resistances at different voltages.
Surge arresters are not generally designed to protect against a direct lightning strike to a
conductor, but rather against electrical transients resulting from lightning strikes occurring in
the vicinity of the conductor. Lightning which strikes the earth results in ground currents
which can pass over buried conductors and induce a transient that propagates outward
towards the ends of the conductor.

29
TYPES OF SURGE ARRESTER
 Low-voltage surge arrester: Apply in Low-voltage distribution system, exchange of
electrical appliances protector, low-voltage distribution transformer windings
 Distribution arrester: Apply in 3KV, 6KV, 10KV AC power distribution system to
protect distribution transformers, cables and power station equipment
 The station type of common valve arrester: Used to protect the 3 ~ 220KV
transformer station equipment and communication system
 Magnetic blow valve station arrester: Use to 35 ~ 500KV protect communication
systems, transformers and other equipment
 Protection of rotating machine using magnetic blow valve arrester: Used to
protect the AC generator and motor insulation
 Line Magnetic blow valve arrester: Used to protect 330KV and above
communication system circuit equipment insulation
 DC or blowing valve-type arrester: Use to protect the DC system’s insulation of
electrical equipment
 Neutral protection arrester: Apply in motor or the transformer’s neutral protection
 Fiber-tube arrester: Apply in the power station’s wires and the weaknesses
protection in the insulated
 Plug-in Signal Arrester: Used to twisted-pair transmission line in order to protect
communications and computer systems
 High-frequency feeder arrester: Used to protect the microwave, mobile base
stations satellite receiver, etc.
 Receptacle-type surge arrester: Use to protect the terminal Electronic equipment
 Signal Arrester: Apply in MODEM, DDN line, fax, phone, process control signal
circuit etc.
 Network arrester: Apply in servers, workstations, interfaces etc.
 Coaxial cable lightning arrester: Used on the coaxial cable to protect the wireless
transmission and receiving system
INSULATOR
An electrical insulator is a material that does not easily conduct an electric current.
Materials typically used to insulate include rubber, plastic and glass. In transformers
and electric motors, varnish is used. Insulating gases such as Sulfur hexafluoride are used in
some switches. Wires that carry electric currents are usually insulated so the electricity goes
to the right place.

30
Insulator can mean not only the material but things that are made of that material. They are
made of various materials such as: glass, silicone, rubber, plastic, oil, and wood, dry cotton,
quartz, ceramic, etc.
The type of insulator will depend on the uses. Insulators have high electrical resistivity and
low conductivity. The insulators prevent the loss of current and make the current more
efficient by concentrating the flow.
TYPE OF INSULATOR
 The pin insulator is the earliest developed insulator. Pin type insulators can have up
to three parts, depending on the amount of voltage.
 The suspension insulator is for voltages above 33KV. Multiple insulators are
connected in series.
 The strain insulator is the same as a suspension insulator but it is used horizontally,
whereas the suspension insulator is used vertically. The strain insulator is used to
relieve the line of excessive tension, which happens when there is dead end of the line
or sharp curve.
WAVE/LINE TRAPPER
Wave trap is used for trapping the high frequency communication signals sent on the
line from the remote substation and diverting to the telecom/tele protection panel in the
substation control room (through coupling capacitor and LMU).
This is relevant in Power Line Carrier Communication (PLCC) systems for communication
among various substations without dependence on the telecom company network. The signals
are primarily tele protection signals and in addition, voice and data communication signals.
The Line trap offers high impedance to the high frequency communication signals thus
obstructs the flow of these signals in to the substation bus bars.

31
UNIT NO: 8 EQUIPMENT’S MAINTENANCE
TRANSFORMER
DAILY/WEAKLY 3-6 MONTHLY YEARLY 5-10 YEAR
 Visual
inspection
 Oil level status
 Cooling System
 Temperature
gauge
 Ground
Connection
 Silica Gel
 Oil leakage/Tap
position
indication/
Motor Drive
Unit
 Space Heater &
Thermostat
setting
 Control Switch
and
Accessories
 Bushing terminal
connection
 Radiator tube valve
 Buchholz Relay/PRD
Check
 Wiring & Terminal
Block
 Tap Changer Operation
 Annual testing (DES test,
DGA test, IR test, C&DF
test, TTR test, WR
test/short circuit test,
Open circuit test,
Buchholz relay functional
& PRD test)
 Diverter Switch
Protective Relay check
 Chemical Analysis
of Oil
 Tangent Delta Test
 Sweep Frequency
Response Analysis
(SFRA) test
 Checking diverter
switching
operation/ Rotation
lack balancing &
overhauling of tap
changer
CIRCUIT BREAKER
 Visual
inspection
 SF6 Gas/Air
Pressure
 Steel Structure
ground
connection
 Operation
counter
 Space Heater &
Thermostat
setting
 Control switches
 ON/OFF
position
 Rated Air
pressure
 Supporting
structure/ Nut
Bolts level
 Wiring and
Terminal Block
 Fall Air
Compressor
check
 HV terminal connection
 Motor Charging time
 Lubrication of
moving/sliding/rolling
parts
 Dashpot oil level check
 Oil level and lockout
check
 Test operation (ON/OFF)
 Annual testing (SF6
purity test, dew point,
contact resistance test,
timing test, minimum
voltage test)
 Anti-pumping, Pole
Discrepancy, SF6 low
pressure and lock out
 Hydraulic oil
replacement

32
ISOLATOR/DISCONNECTOR SWITCH AND EARTH SWITCH
DAILY/WEAKLY 3-6 MONTHLY YEARLY
 Visual inspection
 Contact Alignment
 Operation counter
 Space Heater &
Thermostat setting
 Control switches
 Steel Structure
ground
 Ground mat condition
 Supporting
structure/ Nut
Bolts level
check
 Wiring and
Terminal Block
 HV terminal connection
 Lubrication of moving/sliding/rolling parts
 Porcelain insulator base bearing condition &
lubrication
 Local/Remote/Manual operation check
 Electrical interlocking with circuit breaker
 Mechanical interlocking
 Interlocking between isolator and earth
switching
 Contact resistance test
CURRENT TRANSFORMER
 Oil level
 Ground/HV terminal
Connection
 Space Heater &
Thermostat setting
 Porcelain bushing
condition
 Supporting
structure/
Nut Bolts
level check
 Wiring and
Terminal Block
 Secondary terminal
connection
 IR (Megger) test
 C&DF test of
winding
 DES test,
 DGA test
 Chemical Analysis of
Oil
 Tangent Delta Test
 Knee point voltage test
 Current ratio and
accuracy test
FIRE FIGHTING ARRESTOR
 Water sprinkling system
 Portable fire extinguishers
 Partition well between T/F
 Sand Bucket, Water Buckets and
Shawls
 Fire/Smoke Detectors  Water sprinkling
system
LIGHTING ARRESTOR
 Counter reading
 Ground Connection
 Porcelain/bushing/
corona ring condition
 Supporting structure/
Nut Bolts level check
 Leakage current
monitoring (LCM)
test
 IR test
 C&DF test

33
BUS BAR
 Ground Connection
 Supporting structure/ Nut Bolts
level check
 Equipment connection (Riser
& Droppers)
 Cleaning of
Bus Bar
 IR test
 D.C Hi pot test
 Contact resistance
test for electrical
joints
 Flexible
connectors and
side finings
11 KV CIRCUIT BREAKER
 Abnormal sound/smell
 Panel board indication
 Lamps/Meters
 Protection Relays and
Accessories
 Trolley Rack IN/OUT
way and floor level
 Earth resistance test
 Panel board ground
connection
 Inter-Panel Ground
connection
 Space Heater &
thermostat setting
 Oil replacement
(OCB)
 SF6 gas pressure
 Contact wipe check
(VCB)
 IR test
 D.C Hi Pot
 Contact
resistance test
 Vacuum degree
of VCB
interrupters
(Using VIDAR)
 Power cables
sheath/Shield
grounding
 Circuit
breaker major
maintenance/
Over hauling
STATION GROUNDING SYSTEM
 Equipment ground
connection
 Check direct earthing
of overhead ground
conductor shield/Sky
wire at earth mast
 Earth resistance test
 Fence/Building
ground connection
 Overhead ground
conductor
shield/Sky wire
connection with
earth mesh,
condition fuming
tension or sag
 Earth mesh
conductor
condition and
connection with
earth electrodes
 Earth mesh
integrity test
BATTERY CHARGERS
 Abnormal smell/Sound
 Control switches and
Accessories
 Vermin proofing
 DC grounding
 Float/Boost setting
automatic & manual
 Wiring & terminal block
 Ripple in output DC voltage
 Indicting meter accuracy
 Under/Over voltage problem
 Current limiter setting

34
DC BATTERIES/STATION BATTERY BANK
 Specific gravity of pilot
cell
 Exhaust fan (Battery
Room)
 Electrolyte level in cell
 Battery stand level &
condition
 Voltage of each
cell
 Specific gravity of
each cell
 Vent plugs
 Cell terminal
cleaning
 Manual boost
charge
 Impedance
test
 Inter cell
spacing and
connectors
 Battery ampere
Hours (AH) or
Capacity test
POTENTIAL TRANSFORMER (PT) & CAPACITOR VOLTAGE TRANSFORMER (CVT)
 Oil level
 Ground/HV terminal
Connection
 Space Heater &
Thermostat setting
 Porcelain bushing
condition
 Supporting
structure/ Nut Bolts
level check
 Wiring and
Terminal
Block
 Secondary
terminal
connection
 IR (Megger)
test
 DES test,
 DGA test
 Chemical
Analysis of Oil
 Tangent Delta
Test
 Voltage ratio test
POWER CABLES/CONTROL CABLES
 Cable
marking/Numbering
 Cable terminations & Shield
ground
 Patrolling along the cable route
 Control cable lying
 IR test
 C&DF test

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NTDC 220kV Transmission gird station Internship report