OBRA THERMAL POWER PLANT

INDUSTRIAL TRAINING REPORT THERMAL POWER PLANT
EE DEPARTMENT SRMGPC 6
1. INTRODUCTION
Obra Gajrajnagar is located in Sonbhadra district in the Indian state of Uttar Pradesh,
about 13 km (8.1 mi) from Chopan Railway Station and about 125 km (78 mi) from
Varanasi. The power plant is owned and operated by Uttar Pradesh Rajya Vidyut Utpadan
Nigam There are thirteen functioning units, all of which are coal-fired thermal power
stations. The machinery for the most of the units are from Bharat Heavy Electricals
Limited. The last unit of 200 MW was commissioned in 1982.
UPRVUNL is wholly owned state thermal power utility with present generating
capacity of 5474 MW, operating 4 Thermal Power Stations within Uttar Pradesh. Poised
to contribute in the growth of state, we're in the process of adding further 3960 MW
capacity with super critical technology to our existing fleet.
Uttar Pradesh Rajya Vidyut Utpadan Nigam Limited (UPRVUNL) was constituted
on dated 25.08.1980 under the Companies' Act 1956 for construction of new thermal power
projects in the state sector. The first Thermal Power Station constructed by UPRVUNL
was Unchahar Thermal Power Station of 2X210 MW capacity and it was transferred to
NTPC on dated 13.02.1992. On dated 14.01.2000, in accordance to U.P. State Electricity
Reforms Acts 1999 and operation of U.P. Electricity Reforms Transfer Scheme 2000, U.P.
State Electricity Board, till then responsible for generation, transmission and distribution
of power within the state of Uttar Pradesh, was unbundled and operations of the state sector
thermal power stations were handed over to UPRVUNL.
Today it is looking after operations of 4 thermal power plants located in different
parts of U.P., with a total generation capacity of 5474 MW with planting facility as follows.
And Obra Power plant is one of them.

2. GENERATING UNITS AT OBRA THERMAL POWER
STATION
Stage
Units
No.
Installed
Capacity
Derated
Capacity
Date of
Synchronization
Date of
Commercial
Operation
Original
Equipment
Manufacturers
'A'
TPS
1 50 MW Deleted 15.08.1967 15.08.1967
BOILERS FROM
M/S TAGANROG
& M/S L M Z OF
USSR
2 50 MW Deleted 12.02.1968 11.03.1968 -DO-
3 50 MW Deleted 13.10.1968 13.10.1968 -DO-
4 50 MW Deleted 11.06.1969 16.07.1969 -DO-
5 50 MW Deleted 30.07.1971 30.07.1971 -DO-
'A'
TPS
6 100 MW Deleted 04.10.1973 04.10.1973
M/s Bharat Heavy
Electricals Limited,
India.
7 100 MW 94 MW 14.12.1974 14.12.1974
M/s Bharat Heavy
India.
8 100 MW 94 MW 15.09.1975 01.01.1976
M/s Bharat Heavy
India.
'B'
TPS
9 200 MW 200 MW 26.01.1980 15.03.1980
M/s Bharat Heavy
India.
10 200 MW 200 MW 14.01.1979 06.03.1979
M/s Bharat Heavy
India.
11 200 MW 200 MW 31.12.1977 14.03.1978
M/s Bharat Heavy
India.
'B'
TPS
12 200 MW 200 MW 28.03.1981 29.05.1981
M/s Bharat Heavy
India.
13 200 MW 200 MW 19.07.1982 19.07.1982
M/s Bharat Heavy
India.

3. TYPICAL COAL THERMAL POWER STATION
Typical diagram of a coal-fired thermal power station
1. Cooling tower 10. Steam Control valve 19. Super heater
2. Cooling water pump 11. High pressure steam turbine 20. Forced draught (draft) fan
3. Transmission line (3-phase) 12. Deaerator 21. Reheated
4. Step-up transformer (3-phase) 13. Feed water heater 22. Combustion air intake
5. Electrical generator (3-phase) 14. Coal conveyor 23. Economizer
6. Low pressure steam turbine 15. Coal hopper 24. Air preheater
7. Condensate pump 16. Coal pulverize 25. Precipitator
8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft)
fan
9. Intermediate pressure steam 18. Bottom ash hopper 27. Flue gas stack
turbine
For units over about 200 MW capacity, redundancy of key components is provided
by installing duplicates of the forced and induced draft fans, air preheaters, and fly ash
collectors. On some units of about 60 MW, two boilers per unit may instead be provided.

4. BOILER AND STEAM CYCLE
In the nuclear plant field, steam generator refers to a specific type of large heat
exchanger used in a pressurized water reactor (PWR) to thermally connect the primary
(reactor plant) and secondary (steam plant) systems, which generates steam. In a nuclear
reactor called a boiling water reactor (BWR), water is boiled to generate steam directly in
the reactor itself and there are no units called steam generators. In some industrial settings,
there can also be steam-producing heat exchangers called heat recovery steam generators
(HRSG) which utilize heat from some industrial process. The steam generating boiler has
to produce steam at the high purity, pressure and temperature required for the steam turbine
that drives the electrical generator.
Geothermal plants need no boiler since they use naturally occurring steam sources. Heat
exchangers may be used where the geothermal steam is very corrosive or contains
excessive suspended solids.
A fossil fuel steam generator includes an economizer, a steam drum, and the furnace with
its steam generating tubes and super heater coils. Necessary safety valves are located at
suitable points to avoid excessive boiler pressure. The air and flue gas path equipment
include: forced draft (FD) fan, air preheater (AP), boiler furnace, induced draft (ID) fan,
fly ash collectors
(Electrostatic precipitator or baghouse) and the flue gas stack.
5. TURBO GENERATOR
A turbo generator set or turbine generator set is the compound of a steam turbine or
gas turbine shaft-connected to a fast running electric generator for the generation of electric
power. Large steam-powered turbo generators provide the majority of the world's
electricity and are also used by steam-powered turbo-electric ships.
Small turbo-generators with gas turbines are often used as auxiliary power units (APU,
mainly for aircraft). For base loads diesel generators or gas engines are usually preferred,

since they offer better fuel efficiency, however, such stationary engines have a lower power
density and are built only up to about 10 MW power per unit.
The efficiency of larger gas turbines (50 MW or more) can be enhanced by using a
combined cycle, where the remaining energy of hot exhaust gases is used to generate steam
which drives another steam turbine on same shaft or a separate generator set.
Unlike hydraulic turbines which usually operate at lower speeds (100 to 600 rpm), the
efficiency of a steam turbine is higher at higher speeds and therefore a turbo generator is
used for steam turbines. The rotor of a turbo generator is a non-salient pole type usually
with two poles.
A Turbo generator stator frame
The normal speed of a turbo generator is 1500 or 3000 rpm with four or two poles
at 50 Hz (1800 or 3600 rpm with four or two poles at 60 Hz). Salient rotors will be very
noisy and with a lot of windage loss. The rotating parts of a turbo generator are subjected
to high mechanical stresses because of the high operation speed. To make the rotor
mechanically resistant in large turbo-alternators, the rotor is normally forged from solid
steel and alloys like chromium-nickel-steel or chromium-nickel-molybdenum are used.
The overhang of windings at the periphery will be secured by steel retaining rings. Heavy
non-magnetic metal wedges on top of the slots hold the field windings against centrifugal
forces. Hard composition insulating materials, like mica and asbestos, are normally used

in the slots of rotor. These material can withstand high temperatures and high crushing
forces.
The stator of large turbo generators may be built of two or more parts while in smaller
turbo-generators it is built up in one complete piece.
The general components of a turbo generator are
Stator
- Stator Frame
- Stator Core
- Stator Windings
- End Covers
Rotor
- Rotor Shaft
- Rotor Windings
- Rotor Retaining Rings
# Bearings
# Cooling System
The following auxiliaries are required for operation:
# Oil Supply system
# Excitation System
Quality Assurance checks being followed right from procurement stage to dispatch stage
are enumerated in the following flow chart

STATOR
STATOR FRAME
The stator frame is of welded steel single piece construction. It supports the laminated core
and winding. It has radial and axial ribs having adequate strength and rigidity to minimize
core vibrations and suitably designed to ensure efficient cooling. Guide bars are welded or
bolted inside the stator frame over which the core is assembled. Footings are provided to
support the stator foundation.
STATOR CORE
The stator core is made of silicon steel with high permeability and low hysteresis and eddy
current Losses. The sheets are suspended in the stator frame from insulated guide bars.
Stator laminations are coated with synthetic varnish; are stacked and held between sturdy
steel clamping plates with non-magnetic pressing fingers which are fastened or welded to
the stator frame.
In order to minimize eddy current losses of rotating magnetic flux which interact with the
core is built of thin laminations. Each lamination layer is made of individual segments.
The segments are punched in one operation from electrical sheet steel lamination having a
high silicon content and are carefully deburred. The stator laminations are assembled as
separate cage core without the stator frame. The segments are staggered from layer to layer
so that a core of high
Mechanical strength and uniform permeability to magnetic flux is obtained. On the outer
circumference the segments are stacked on insulated rectangular bars which hold them in
position.
To obtain optimum compression and eliminate looseness during operation the laminations
are hydraulically compressed and heated during the stacking procedure. To remove the
heat, spaced segments are placed at intervals along the core length which divide the core
into sections to provide wide radial passages for cooling air to flow.

STATOR WINDING CONSTRUCTION
The stator windings consist of two layers made of individual bars. To minimize losses,
bars are composed of separately insulated strands which are transposed by 360 degrees.
To minimize stray losses in end windings, strands of top and bottom bars are separately
brazed and insulated from each other.
Each bar consists of a large number of separately insulated strands to reduce the skin effect
losses. In straight slot portion, the strands are transposed by 360 degrees. The transposition
provides for mutual neutralization of voltages induced in the individual strands due to slot
cross field and ensures that no or small circulating currents exist in the bar interior. The
current flowing through the bar is thus distributed uniformly over the entire cross section
of a bar so that the current dependent losses will be reduced.
INSULATION OF BARS
High voltage insulation is provided with thermosetting system. A voltage insulation
obtained by vacuum press impregnation is particularly void free with excellent electrical,
mechanical and thermal properties. To prevent corona discharge between the insulation
and slot wall, a final layer of conductive tape is applied to the surface of all bars within the
slot range. All bars are conditionally provided with an end corona protection to control the
electric filed at the transition from slot to the end winding portion and to prevent the
formation of creep age sparks.
VACCUM PRESS IMPREGNATED MICALASTIC HIGH VOLTAGE
INSULATION
The high voltage insulation is provided according to the proven resin poor mica base of
thermosetting epoxy system. Several half overlapped continuous layer of resin poor mica
type are applied over the bars. The number of layers or thickness of insulation depends on
machine voltage.

The bars are inserted into the slots with very small lateral clearance and wedged with
packers. To prevent moment of end windings in circumferential direction, spacer blocks
are arranged between the bars and firmly with treated glass tapes. To minimize the effect
of radial forces, winding holders and insulated rings are used to support the overhang.
The stator is impregnated in a tank under vacuum and pressure with low viscosity epoxy
resin that penetrates the winding thoroughly. After impregnation, the stator is cured at at
appropriate temperature in an oven.
The high voltage insulation thus obtained is characterized by its excellent electrical,
mechanical and thermal properties. Its moisture absorption is extremely low and it is oil
resistant. The behavior of the insulation is far superior to any other conventional mica tape
insulation system.
CORONA PROTECTION
To prevent a potential difference and possible corona discharges between the insulation
and slot wall, the slot sections of bars are provided with an outer corona protection. This
protection consists of polyester fleece tape impregnated in epoxy resin with carbon and
graphite as filters.
At the transition from slot to the end winding portion of stator bars a semi-conductive tape
made of polyester fleece is impregnated with silicon carbide as filler is applied for a
specific length. This ensures uniform control of the electric field and prevents the
formation of corona discharge during operation and performance of HV tests.
END COVERS
The end covers are made of fabricated steel or aluminum alloy castings. They are employed
with guide vanes on inner side for ensuring uniform distribution of cooling air or gas.

ROTOR
Solid rotors are manufactured from forged alloy steel with suitable alloying elements to
achieve very high mechanical and superior magnetic properties. Rectangular or trapezoidal
rotors slots are accurately machined to close tolerances on slot milling machine. For
indirectly cooled generator rotors, ventilation slots are machined in the teeth.
For directly cooled rotors, Sub slots are provided for cooling Generators rotors of 1500
RPM are of round laminated construction. Punched and varnished laminations of high
tensile steel are mounted over machined shaft are firmly clamped by end clamping plates.
ROTOR SHAFT
Rotor shaft is a single piece solid forming manufactured form a vacuum casting. It is forged
from a vacuum cast steel ignot. Slots for insertion or the field winding are milled into rotor
body. The longitudinal slots are disturbed over the circumference such that two solid poles
are obtained.
To ensure that only a high quality product is obtained, strength tests, material analysis and
ultrasonic tests are performed during the manufacture of rotor. The high mechanical
stresses resulting from the centrifugal forces and short circuit torque call for a high
specified mechanical and magnetic properties as well as homogeneous forging. After
completion, the rotor is balanced in various planes at different speeds and then subjected
the rotor is balanced in various planes at different speeds and then subjected to an over
speed test at 120% of the rated speed for two minutes.
The rotor consists of electrically active portion and two shaft ends. Approximately 60% of
rotor body circumference have longitudinal slots which hold the field winding. Slot pitch
is selected so that the two solid poles are displaced by 180 degrees. The rotor wedges act
as damper winding within the range of winding slots. The rotor teeth at the ends of rotor

body are provided with axial and radial holes enabling the cooling air to be discharged into
the air gap after intensive cooling of end windings
ROTOR WINDINGS
The windings consist of several coils inserted into the slots and series connected such that
two coil groups form one pole. Each coil consists of several series connected turns, each
of which consists of two half turns connected by brazing in the end section. The rotor
bearing is made of silver bearing copper ensuring an increased thermal stability. The
individual turns of coils are insulated against each other by interlayer insulation. L-shaped
strips of laminated epoxy glass fiber fabric with nomex filter are used for slot insulation.
The slot wedges are made o high electrical conductivity material and thus act as damper
windings. At their ends the slot wedges are short circuited through the rotor body.
CONSTRUCTION
The field winding consists of several series connected coils inserted into the longitudinal
slots of rotor body. The coils are wound so that two poles are obtained. The solid
conductors have a rectangular cross section and are provided with axial slots for radial
discharge or cooling air. All conductors have identical copper and cooling duct cross
section. The individual bars are bent to obtain half turns. After insertion into one slot
constitute one coil. The individual coils of rotor are connected in a way that one north and
one south pole is obtained.
CONDUCTOR MATERIAL
The conductors are made of copper with a silver content of approximately 0.1%. As
compared to electrolytic copper, silver alloyed copper features high strength properties at
high temperatures so that coil deformations due to thermal stresses are eliminated.

INSULATION
The insulation between the individual turns is made of layer of glass fiber laminate. The
coils are insulated from the rotor body with L- shaped strips of glass fiber laminate with
nomex interlines. To obtain the required leakage paths between the coil and rotor body
thick top strips of glass fiber laminate are inserted below top wedges. The top strips are
provided with axial slots of the same cross section and spacing as used on the rotor
winding.
ROTOR SLOT WEDGES
To protect the winding against the effects of centrifugal forces, the winding is secured in
the slots with wedges. The slot wedges are made of copper alloy featuring high strength
and good electrical conductivity. They are also used as damper winding bars. The slot
wedges extend beyond the shrink seats of retaining rings. The wedge and retaining rings
act on the damper winding in the event of abnormal operations. The rings act as a short
circuit rings in the damper windings.
END WINDING BRACING
The spaces between the individual coils in the end winding are filled with insulated
members that prevent coil movement. Two insulation plates held by HGL-high glass
laminate plates separate the different cooling zones the overhangs on either sides.
ROTOR RETAINING RINGS
The centrifugal forces of the rotor end winding are contained by single piece rotor retaining
rings. Retaining rings are made of non-magnetic high strength steel in order to reduce stray
losses. Each retaining ring with its shrink fitted. Insert ring is shrunk on the rotor in an
overhang position. The retaining ring is secured in the axial position by snap rings.
The rotor retaining rings withstand the centrifugal forces due to end windings. One end of
each ring is shrunk fitted on the rotor body while the other end overhangs the end windings

without contact on the rotor shaft. This ensures an unobstructed shaft deflection at end
winding.
The shrunk on hub on the end of the retaining ring serves to reinforce the retaining ring
and secures the end winding in the axial direction at the same time.
A snap ring is provided against axial displacement of retaining ring. The shrunk seat of
currents. To reduce the stray losses and have high strength, The rings are made of
nonmagnetic, cold worked materials.
ROTOR FANS
The cooling air in generator is circulated by two axial flow fans located on the rotor shaft
one at each end. To augment the cooling of the rotor winding, the pressure established by
the fan works in conjunction with the air expelled from the discharge parts along the rotor.
The blades of the fan have threaded roots for being screwed into the rotor shaft. The blades
are drop forged from Aluminium alloy. Threaded root fastenings permit angle to be
changed. Each blade is secured at its root with a threaded pin.
BEARINGS
The turbo generators are provided with pressure lubricated self - aligning elliptical type
bearings to ensure higher mechanical stability and reduced vibration in operation. The
bearings are provided with suitable temperature element devices to monitor bearing metal
temperature in operation.
The temperature of each bearing is monitored with two RTDs (Resistance Thermo
Detectors) embedded in the lower bearing sleeve such that the measuring point is located
directly below the babbit. These RTDs are monitored a temperature scanner in the control
panel and annunciated if the temperature exceeds the prescribed limits. All bearings have
provisions for fitting vibration pickups to monitor shaft vibrations.

To prevent damage to the journals due to shaft currents, bearings and oil piping on either
side of the non-drive end bearings are insulated from the foundation frame.
For facilitating and monitoring the healthiness of bearing insulation, split insulation is
provided.
VENTILATION AND COOLING
Turbo generators are designed with the following ventilation systems:
 Closed circuit air cooling with water or air coolers mounted in the pit.
 Closed circuit hydrogen cooling with water or hydrogen coolers mounted axially
on the stator frame.
The fan design usually consists of two axial fans on either made of cast aluminum with
integral fan blades or forged and machined aluminum with integral fan blades or forged
and machined aluminum alloy blades screwed to the rotor. In case of 1500 RPM
generators, fabricated radial fans are provided.
EXCITER
The exciter is brushless mainly consisting of:
- Rectifier wheels
- Three phase main exciter
- Three phase pilot exciter
- Metering and supervisory equipment
The brushless exciter is an AC exciter with rotating armature and stationary field. The
armature is connected to rotating rectifier bridges for rectifying AC voltage induced in the
armature to DC voltage.
The pilot exciter is a PMG (Permanent Magnet Generator). The PMG is also an AC
machine with stationary armature and rotating field (the permanent magnets).When the

generator rotates at the rated speed, the PMG generates 220v at 150 Hz to provides power
supply to automatic voltage regulator.
A common shaft carries the rectifier wheels the rotor of the main exciter and the permanent
magnet rotor of the pilot exciter. The shaft is rigidly coupled to the generator rotor and
exciter rotors are then supported on three bearings.
6. DIFFERENT TRANSFORMERS IN THERMAL POWER
PLANT
In Thermal and Nuclear Power Plants different types of power transformers are employed
GENERATOR TRANSFORMER:
This is the main power transformer employed in the power plant. It steps the voltage
from 21kV to 230 or 400kV and delivers the power. Stepping up the voltage reduces the
transmission losses which occur during the power transmission to long distances. The
rating of this transformer (MVA rating) will be almost equal to the alternator or generator
rating.
Generator Step-up Transformer units are used to increase the voltage of a generator
and connect the supply to a bus bar. Generator Transformers are also used to limit the fault
level of the generator in case of a fault. Transformers used for these applications are called
Generator Step-up Units. These Transformers are designed to operate at near full load.

UNIT AUXILIARY TRANSFORMERS:
These transformers are connected to the Generator Transformer bus. These transformers
steps down the voltage from 230kV or 400kV to 6.6kV (230/6.6kV or 400kV/6.6kV) and
supply the power to the electrical auxiliaries present in the plant (motors, drives, lighting
and other plant loads).
STATION TRANSFORMER OR STARTUP TRANSFORMER:
This transformer provides electrical power to the plant during start up when no supply is
available to the plant (generator is not operating). It also steps down the voltage like unit
auxiliary transformers and supply power the lant auxiliaries.
Station Transformer and Unit Auxiliary Transformers are connected to the grid, so that
they can get power when Turbo-Generator is not in operation and supply power to the plant
auxiliaries.
Small transformers provide a small amount of isolated power for a more powerful
switching power supply. If the size of such a transformer is smaller than needed for
complete control and drive of the larger power supply, the small transformer works as a
startup transformer while a winding in the bigger transformer in the bigger power supply
kicks in and provides enough voltage and current for its complete operation.

AUXILIARY TRANSFORMERS:
These are small distribution transformers supply power to plant electrical auxiliaries rated
at 415V by stepping down the voltage (6.6kV/415V).
Auxiliary transformers are used in power system. In thermal power plant with the main
transformer a number of auxiliary transformers are required according to power
requirements. Now the auxiliary transformers are basically used to provide supply to the
power equipment they don't step up or step down the transmission voltage they are only
used to supply power for the equipment that are running in the whole power plant. Their
rating is 15/6.6kv.

7. TRANSFORMER COOLING METHODS
No transformer is truly an 'ideal transformer' and hence each will incur some losses, most
of which get converted into heat. If this heat is not dissipated properly, the excess
temperature in transformer may cause serious problems like insulation failure. It is
obvious that transformer needs a cooling system. Transformers can be divided in two
types as (i) dry type transformers and (ii) oil immersed transformers. Different cooling
methods of transformers are
 For dry type transformers
1. Air Natural (AN)
2. Air Blast
 For oil immersed transformers
1. Oil Natural Air Natural (ONAN)
2. Oil Natural Air Forced (ONAF)
3. Oil Forced Air Forced (OFAF)
4. Oil Forced Water Forced (OFWF)
Cooling methods for Dry type Transformers
Air Natural or Self air cooled transformer
This method of transformer cooling is generally used in small transformers (up to 3
MVA). In this method the transformer is allowed to cool by natural air flow surrounding
it.
Air Blast
For transformers rated more than 3 MVA, cooling by natural air method is inadequate. In
this method, air is forced on the core and windings with the help of fans or blowers. The
air supply must be filtered to prevent the accumulation of dust particles in ventilation
ducts. This method can be used for transformers up to 15 MVA.

Cooling methods for Oil Immersed Transformers
a. Oil Natural Air Natural (ONAN)
This method is used for oil immersed transformers. In this method, the heat generated in
the core and winding is transferred to the oil. According to the principle of convection,
the heated oil flows in the upward direction and then in the radiator. The vacant place is
filled up by cooled oil from the radiator. The heat from the oil will dissipate in the
atmosphere due to the natural air flow around the transformer. In this way, the oil in
transformer keeps circulating due to natural convection and dissipating heat in
atmosphere due to natural conduction. This method can be used for transformers up to
about 30 MVA.

b. Oil Natural Air Forced (ONAF)
The heat dissipation can be improved further by applying forced air on the dissipating
surface. Forced air provides faster heat dissipation than natural air flow. In this method,
fans are mounted near the radiator and may be provided with an automatic starting
arrangement, which turns on when temperature increases beyond certain value. This
transformer cooling method is generally used for large transformers upto about 60 MVA.
Oil Forced Air Forced (OFAF)
In this method, oil is circulated with the help of a pump. The oil circulation is forced
through the heat exchangers. Then compressed air is forced to flow on the heat exchanger
with the help of fans. The heat exchangers may be mounted separately from the
transformer tank and connected through pipes at top and bottom as shown in the figure.
This type of cooling is provided for higher rating transformers at substations or power
stations.

Oil Forced Water Forced (OFWF)
This method is similar to OFAF method, but here forced water flow is used to dissipate
hear from the heat exchangers. The oil is forced to flow through the heat exchanger with
the help of a pump, where the heat is dissipated in the water which is also forced to flow.
The heated water is taken away to cool in separate coolers. This type of cooling is used in
very large transformers having rating of several hundred MVA.

8. SWITCHYARD & ITS EQUIPMENTS
The electricity substation is a network of electrical equipment which is connected in
a structured way in order to supply electricity to end consumers. There is numerous
electrical substation components like outgoing and incoming circuitry each of which
having its circuit breakers, isolators, transformers, and busbar system etc. for the smooth
functioning of the system. The power system is having numerous ingredients such as
distribution, transmission, and generation systems and Substations act as a necessary
ingredient for operations of the power system. The substations are entities from which
consumers are getting their electrical supply to run their loads while required power quality
can be delivered to the customers by changing frequency and voltage levels etc..
The electricity substation designs are purely dependent on the need, for instance, a single
bus or complex bus system etc. Moreover, the design is also dependent on the application
as well, for instance, indoor substations, generation substations, transmission substations,
pole substations, outdoor substation, converter substation, and switching substation etc.
There is a need of collector substation as well in cases of large power generating systems
e.g. multiple thermal and hydropower plants connected together for transfer of power to a
single transmission unit from numerous co-located turbines.
The following are major electrical components of substations and their working. Each
component functions are explained in detail with machinery, substation components
diagram is also given above for your reference.
List of Electrical Substation Equipments-
1. Instrument Transformers
2. Current Transformer
3. Potential Transformer
4. Conductors
5. Insulators
6. Isolators
7. Busbars
8. Lightning Arrestors
9. Circuit Breakers

10.Relays
11.Capacitor Banks
12.Batteries
13.Wave Trapper
14.SwitchYard
15.Metering and Indication Instruments
16.Equipment for Carrier Current
17.Prevention from Surge Voltage
18.The Outgoing Feeders
Instrument Transformers:
The instrument transformer is a static device utilized for reduction of higher currents and
voltages for safe and practical usage which are measurable with traditional instruments
such as digital multi-meter etc. The value range is from 1A to 5A and voltages such as
110V etc. The transformers are also used for actuation of AC protective relay through
supporting voltage and current. Instrument transformers are shown in the figure below and
its two types are also discussed underneath.
Current Transformer:
A current transformer is a gadget utilized for the transformation of higher value currents
into lower values. It is utilized in an analogous manner to that of AC instruments, control
apparatus, and meters. These are having lower current ratings and are used for maintenance
and installation of current relays for protection purpose in substations.

Potential Transformer:
The potential transformers are similar in characteristics as current transformers but are
utilized for converting high voltages to lower voltages for protection of relay system and
for lower rating metering of voltage measurements.
Conductors:
Conductors are the materials which permit flow of electrons through it. The best conductors
are copper and aluminum etc. The conductors are utilized for transmission of energy from
place to place over substations.
Insulators:
The insulators are the materials which do not permit flow of electrons through it. Insulators
are resisting electric property. There are numerous types of insulators such as shackle,
strain type, suspension type, and stray type etc. Insulators are used in substations for
avoiding contact with humans or short circuit.

Isolators:
The isolators in substations are mechanical switches which are deployed for isolation of
circuits when there is an interruption of current. These are also known with the name of
disconnected switches operation under no-load conditions and are not fortified with arc-
quenching devices. These switches have no specific current breaking value neither these
have current making value. These are mechanically operated switches.
Busbars
The busbar is among the most important elements of the substation and is a conductor
which carries current to a point having numerous connections with it. The busbar is a kind
of electrical junction which has outgoing and incoming current paths. Whenever a fault
occurs in the busbar, entire components connected to that specific section should be tripped
for giving thorough isolation in a small time, for instance, 60ms for avoiding danger rising

due to conductor’s heat. These are of different types such as ring bus, double bus, and
single bus etc. A simple bus bar is shown in the figure below which is considered as one
of the most vital electrical substation components.
The Lightning Arresters:
The lightning arresters can be considered as the first ever components of a substation.
These are having a function of protecting equipment of substation from high voltages and
are also limiting the amplitude and duration of the current’s flow. These are connected
amid earth and line i.e. connected in line with equipment in the substation. These are meant
for diversion of current to earth if any current surge appears hence by protecting insulation
as well as conductor from damages. These are of various types and are distinguished based
on duties.
Circuit Breakers:

The circuit breakers are such type of switches utilized for closing or opening circuits at the
time when a fault occurs within the system. The circuit breaker has 2 mobile contacts which
are in OFF condition in normal situations. At the time when any fault occurs in the system,
a relay is sending the tripped command to the circuit breaker which moves the contacts
apart, hence avoiding any damage to the circuitry.
Relays:
Relays are a dedicated component of electrical substation equipment for the protection of
system against abnormal situations e.g. faults. Relays are basically sensing gadgets which
are devoted for sensing faults and are determining its location as well as sending
interruption message of tripped command to the specific point of the circuit. A circuit
breaker is falling apart its contacts after getting the command from relays. These are
protecting equipment from other damages as well such as fire, the risk to human life, and
removal of fault from a particular section of the substation. Following is the substation
component diagram is known as a relay.
Relays

Capacitor Banks:
The capacitor bank is defined as a set of numerous identical capacitors which are connected
either in parallel or series inside an enclosure and are utilized for the correction of power
factor as well as protection of circuitry of the substation. These are acting like the source
of reactive power and are thus reducing phase difference amid current and voltage. These
are increasing the capacity of ripple current of supply and avoid unwanted selves in the
substation system. The use of capacitor banks is an economical technique for power factor
maintenance and for correction of problems related to power lag.
Capacitor Bank in Substation
Batteries:
Some of the important substation parts such as emergency lighting, relay system, and
automated control circuitry are operated through batteries. The size of the battery bank is
depending on the voltage required for operation of the DC circuit respectively. The storage
batteries are of two basic types i.e. acid-alkaline batteries and lead-acid batteries. The lead
acid batteries are of the most common type and used in substations in abundance as these
provide high voltages and are cheaper in cost.
Wave Trapper:

The wave trapper is one of the substation components which is placed on the incoming
lines for trapping of high-frequency waves. The high-frequency waves which are coming
from nearby substations or other localities are disturbing the current and voltages, hence
its trapping is of great importance. The wave trapper is basically tripping high-frequency
waves and is then diverting the waves into telecom panel.
Switchyard:
The switchyards, switches, circuit breakers, and transformers for the connection and
disconnection of transformers and circuit breakers. These are also having lighting arrestors
to protect the substation or power station from strokes of natural lighting.
Metering and Indication Instruments:
There are numerous instruments for metering and indication in each substation such as
watt-meters, voltmeters, ammeters, power factor meters, kWh meters, volt-ampere meters,
and KVARH meters etc. These instruments are installed at different places within
substation for controlling and maintaining values of current and voltages. For instance,

33/11KV substation equipment will comprise digital multi-meters for various readings
of currents and voltages.
Equipment for Carrier Current:
The equipment of carrier current is installed in the substation for the purpose of
communication, supervisory control, telemetry, and/or relaying etc. Such equipment is
often mounted on a room which is known as carrier room and is connected across the power
circuit of high voltages.
Prevention from Surge Voltage:
The transient of overvoltages substation system is because of inherent and natural
characteristics. There are several reasons for overvoltages which may be caused due to a
sudden alteration in conditions of the system e.g. load rejection, faults, or switching
operations etc. or because of lighting etc. The types of overvoltages can be classified into
two i.e. switching generated or lightning generated. However, the scale of overvoltages
could be over maximum allowable voltage levels, hence these are required to be protected
and reduced for avoiding damage to instruments, equipment, and lines of a substation. In
this way, the performance of the substation system can be enhanced.
The Outgoing Feeders:
There are numerous outgoing feeders which are connected to that of substations. Basically,
the connection is with a bus of the substation for carrying power from the substation to
service points. The feeders can hug overhead streets, underground, underneath streets, and
are carrying electrical power to that of distribution transformers at near or farther premises.
The isolator in substation and breaker of the feeder are considered as entities of the
substation and are of metal-clad typically. Whenever a fault is occurring in the feeder, the
protection is detecting and the circuit breaker is opened. After detection of fault through
manual or automatic way, there are more than one attempts for re-energizing the feeder.

9. ELEMENTS OF A SUBSTATION
1. Primary power lines
2. Ground wire
3. Overhead lines
4. Transformer for measurement of electric voltage
5. Disconnect switch
6. Circuit breaker
7. Current transformer
8. Lightning arrester
9. Main transformer
10.Control building
11.Security fence
12.Secondary power lines

10. CONCLUSION
Due to tight balance in the supply and demand of electricity caused by rapid
economic growth, the existing power plants have recorded high availability as more than
90% which results in restrictions in proper maintenance work time. This has, on the other
hand, caused electrical outages and a fall in power output and has aggravated the present
tight supply and demand balance. India has abundant coal resources and around 66% of its
present installed capacity is coal-fired thermal power. As coal will remain the dominant
fuel for electric power generation according to India’s eleventh five-year electric
development plan, it is vital to enhance its technical capability for the efficient operation
of existing power plants, such as plant efficiency improvement and life-extension
management, in addition to the normal plant operation and maintenance. In recent years,
the worldwide reduction of environmental impact has been called for. In India as the fourth-
largest energy consumer, an awareness-raising on climate change issues and actual steps
to introduce countermeasure technologies have become important issues. Under such
circumstances, the government of India has requested the government of Japan to conduct
a study on improving the operation of the country’s thermal power plants, titled “The Study
on Enhancing Efficiency of Operating Thermal Power Plants in NTPC-India.” In response
to this request, the Japan International Cooperation Agency (“JICA”) decided to conduct
the Study, and subsequently selected a consortium comprised of Electric Power
Development Co., Ltd., Kyushu Electric Power Co., Inc., and The Chugoku Electric Power
Co., Inc. to serve as a consultant in implementing and operating the Study on December,
2008

11. ADVANTAGES
 Fuel used is cheaper.
 Smaller space is required compared to hydro power plant.
 Economical in initial cost compared to hydro plants and running costs are less
compared to gas plants or diesel plants.
 Thermal plants can be placed near load centers unlike hydro and nuclear plants.
Hence transmission of power losses can be minimized.
 Thermal plants are able to respond to the load demand more effectively and supports
the performance of the electrical grid.
 Steam plants can withstand for overload for certain extent.
12. DISADVANTAGES
 Higher maintenance and operational costs.
 Pollution of the atmosphere.
 Huge requirement of water.
 Handling of coal and disposal of ash is quite difficult and requires large area.
 Gestation period (period for commissioning of plant) takes long time.
 Efficiency of thermal plant is quite less (30-35%).
 Operational cost of thermal plant is more costlier compared to hydro and nuclear
plant.

OBRA THERMAL POWER PLANT

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