Mtps project report

ACKNOWLEDGEMENT
The dissertation has been prepared based on the vocational training
undergone in a highly esteemed organization of Eastern region, a pioneer
in Generation Transmission & Distribution of power, one of the most
technically advanced & largest thermal power stations in West Bengal, the
Mejia Thermal Power Station (M.T.P.S), under DVC. I would like to
express my heartfelt gratitude to the authorities of Mejia Thermal Power
Station for providing me such an opportunity to undergo training in the
thermal power plant of DVC, MTPS. I would also like to thank the
Engineers, highly experienced without whom such type of concept building
in respect of thermal power plant would not have been possible. Some of
them are:
1) Mr. Parimal Kumar Dubey
2) Mr. Prabhat Dalbera
3) Mr. Bidyut Majhi
4) Mr. Sumit Bhowmick
5) Mr. Ratan Dang
6) Mr. Bablu Das
7) Mrs. Moumita Saha

CONTENTS
1. Introduction
2. Overview of Thermal Power Plant
3. Coal Handling Plant
4. Water Treatment Plant
5. Boiler system & Auxiliaries
6. Ash Handling Plant
7. Electrostatic Precipitator
8. Steam Turbine
9. Cooling Tower
10.Chimney
11.Electrical Operation
11.1. Generator and Excitation Systems
11.2. Transformer
11.3. Switchyard and Protection system
11.4. Industrial batteries
11.5. Battery Chargers
11.6. Electrical Testing
12.Conclusion
13.Bibliography

INTRODUCTION
Damodar Valley Corporation was established on 7th July 1948.It is the most
reputed company in the eastern zone of India. DVC in established on the Damodar
River. It also consists of the Durgapur Thermal Power Plant in Durgapur. The
MTPS under the DVC is the largest thermal plant in West Bengal. It has the
capacity of 2340MW with 4 units of 210MW each, 2 units of 250MW each & 2
units of 500 MW each. With the introduction of another two units of 500MW that
is in construction it will be the largest in West Bengal. Mejia Thermal Power
Station also known as MTPS is located in the outskirts of Raniganj in Bankura
District. It is one of the 5 Thermal Power Stations of Damodar Valley Corporation
in the state of West Bengal. Mejia Thermal Power Station (MTPS), equipped with
3x210 MW thermal units, has for its power management one 220 KV switchyard,
one 33 KV switchyard at Mejia and another 33 KV switchyard at Barrage Intake
pump house (BIPH) near Durgapur Barrage. The units generate power at 15.75
KV levels, which is then stepped up to 220 KV through 250 MVA15.75/240 KV-
YD1 connected Generator Transformer (GT), and fed to bus. The 220 KV bus
bar arrangements are formed in double main bus (MB) and one transfer bus (TB)
scheme. The 220 KV switchyard connected to 220 KV switchyard at CTPS by
133 Kms double circuit line , 220 KV switchyard at DTPS by 38 Kms double
circuit line, 220 KV switchyard at Kalyaneshwari Grid substation by 65 Kms
double circuit line for evacuation of power.

TECHNICAL SPECIFICATION OF MTPS
Details of MTPS Generating Units
Gen. unit Name of
manufactures
Capacity (in MW) Year of
commissioning
U#1 BHEL 210 Mar. 1996
U#2 BHEL 210 Mar. 1998
U#3 BHEL 210 Sep. 1999
U#4 BHEL 210 Feb. 2005
U#5 BHEL 250 Feb. 2008
U#6 BHEL 250 Sep. 2008
U#7 BHEL 500 Aug. 2011
U#8 BHEL 500 Aug. 2012
 Total Energy Generation: - 2340 MW
 Source of Water: - Damodar River
 Sources of Coal: - B.C.C.L and E.C.L, also imported
from Indonesia

OVERVIEW OF THERMAL POWER PLANT
A thermal power plant continuously converts the energy stored in the fossil
fuels(coal, oil, natural gas) into shaft work and ultimately into electricity. The
working fluid is water which is sometimes in liquid phase and sometimes in
vapour phase during its cycle of operation. Energy released by the burning of fuel
is transferred to water in the boiler to generate steam at high pressure and
temperature, which then expands in the turbine to a low pressure to produce shaft
work.

The steam leaving the turbine is condensed into water in the condenser where
cooling water from a river or sea circulates carrying away the heat released during
condensation. The water is then fed back to the boiler by the pump and the cycle
continues. The figure below illustrates the basic components of a thermal power
plant where mechanical power of the turbine is utilised by the electric generator
to produce electricity and ultimately transmitted via the transmission lines.

COAL HANDLING PLANT
Source of coal: B.C.C.L and E.C.L, also imported from Indonesia
Bituminous and Subbituminous type coal is transported from coal mines to
MTPS by bottom open bottom release (BOBR) type wagon. Then coal is
unloaded on table hopper and from there by plough hopper coal is loaded on
conveyor belt 1A & 1B. Secondly, via the transfer point the coal goes to
another conveyer belt 2A & 2B and then to the crusher house. The coal after
being crushed to 20mm size goes to the stacker via the conveyer belt 3A & 3B
for being stacked or reclaimed and finally to the bunker of the desired unit by
conveyor belt 4A & 4B , 5A & 5B, 6A & 6B. ILMS is the inline magnetic
separator where all the magnetic particles associated with coal get separated.
From bunker, coal (20mm) goes to coal feeder then to coal mill (ball mill,
bowl mill, tube mill) where coal is pulverised to fine powder. From coal mill,
pulverised coal is conveyed to classifier and from that through 4 channels coal
is pushed to furnace by Primary Air (PA) fan.

WATER TREATMENT PLANT
Raw water supply:
Raw water is received from Durgapur barrage at the reservoir (2* 2.75lacs meter
cube capacity) of MTPS is passed through Water Pre-Treatment Plant to separate
suspended impurities and dissolved gases including organic substance and then
through De-mineralised Plant to separate soluble impurities.
Aeration:
Raw water is pumped in the aerator through Raw-aerator pump from the reservoir
and then the raw water is sprayed over cascade aerator in which water flows
downwards over many steps in the form of thin waterfalls. Cascading increases
surface area water to facilitate easy separation of dissolved undesirable gases (like
hydrogen sulphide, ammonia, volatile organic compound etc.) or to help in

oxygenation of mainly ferrous ions in presence of atmospheric oxygen and
sunlight to ferric ions.
Coagulation:
Coagulation takes place in clariflocculator. Coagulant destabilises suspended
solids and agglomerates them into heavier floc, which is separated out through
sedimentation. Prime chemicals used for coagulation are alum, poly-aluminium
chloride (PAC).
Filtration:
Filters remove coarse suspended matter and remaining floc or sludge after
coagulation and also reduce the chlorine demand of the water. Some filtrated clear
water is then sent to the condenser.
Chlorination:
Neutral organic matter is very heterogeneous i.e. it contains many classes of high
molecular weight organic compounds. Humid substances constitute a major
portion other dissolved organic carbon from surface waters. They are complex
mixtures of organic compounds with relatively unknown structures and chemical
composition.
DM (Demineralised Water) Plant
In De-mineralised Plant, the filter water of Water Treatment Plant is passed
through the pressure sand filter (PSF) to reduce turbidity and then through
activated charcoal filter (ACF) to adsorb the residual chlorine and iron in filter
water. After the filters water enters the strong acid ion exchanger
(SAC) resin which can completely remove all ionisable salts present in the water
and forms strong acid (e.g. H2SO4) and weak acid (e.g. H2CO3).
After SAC resin water along with strong acid (H2SO4) and strong base (H2CO3)
is passed to the strong base anion (SBA) exchanger resin. It breaks the strong acid
in the water.

Then the water is passed to the Degassifier tank where the blower blows air into
the chamber and as a result unstable carbonic acid (H2CO3) of the water breaks
to liberate CO2 gas.
The mixed bed unit is a single column or unit containing both cation and anion
exchange resins intimately mixed together. When water is passe through such a
unit it comes into contact alternately with grains of cations and anion resin, so
that the water is subject to an almost infinite number of demineralization stages.
In operation it behaves like a large number of two stag demineralization in
series,with the results that it will produce final water,which is neutral and has
very low residual disolved solids content.
Primary amine ,NH3 is dosed at MB outlet to increase the pH value 8.5 -9.0 ; the
enhance pHvalue is minimised ion pick-up from steel pipe that connect up
toDMWT.
Final water condition after MB vessel output is: SiO2 IS 0.02 ppm max(ppm
means mg/lit), pH 6.8-7.2 and conductivity 0.30us/cm.
After this the water is taken to DM water storage tanks(DMWT).

BOILER SYSTEM
BOILER: Working principle of Boiler (Steam Generator): In Boiler, steam is
generated from demineralized water by the addition of heat. The heat added
has two parts: sensible heat and latent heat. The sensible heat raises the
temperature and pressure of water as well as steam. The latent heat converts
water into steam (phase change). This conversion is also known as boiling of
water, which is dependent on pressure and corresponding temperature.
Thermodynamically, boiling is a process of heat addition to water at constant
pressure & temperature. The quantity of latent heat decreases with increase
in pressure of water and it becomes zero at 221.06 bars. This pressure is
termed as critical pressure. The steam generators are designated as sub-critical
or super critical based on its working pressure as below critical or above critical
pressure. The steam, thus formed is dry & saturated. Further, addition of heat
raises the temperature and pressure of steam, which is known as superheated
steam. The differential specific weight between steam and water provides the
driving force for natural circulation during the steam generation process.
This driving force considerably reduces at pressure around 175 Kg/cm2
and is not
able to overcome the frictional resistance of its flow path. For this, forced or
assisted circulation is employed at higher sub-critical pressure range due to
the reason of economy. But, at supercritical pressures and above, circulation is
forced one (such boiler is called once through boiler).
Important parts of Boiler & their functions:
Economizer: Feed water enters into the boiler through economizer. Its function
is to recover residual heat of flue gas before leaving boiler to preheat feed water
prior to its entry into boiler drum. The drum water is passed through down-
comers for circulation through the water wall for absorbing heat from
furnace. The economizer recirculation line connects down-comer with the
economizer inlet header through an isolating valve and a non-return valve
to protect economizer tubes from overheating caused by steam entrapment
and starvation. This is done to ensure circulation of water through the tubes
during initial lighting up of boiler, when there is no feed water flow through
economizer.
Drum: Boiler drum is located outside the furnace region or flue gas path.
This stores certain amount of water and separates steam from steam-water
mixture. The minimum drum water level is always maintained so as to
prevent formation of vortex and to protect water wall tubes (especially its

corner tubes) from steam entrapment / starvation due to higher circulation ratio
of boiler. The secondary stage consists of two opposite bank of closely
spaced thin corrugated sheets which direct the steam through a tortuous
path and force the remaining entrained water against the corrugated plates.
Since, the velocity is relatively low, this water does not get picked up
again but runs down the plates and off the second stage lips at the two steam
outlets. From the secondary separators, steam flows uniformly and with
relatively low velocity upward to the series of screen dryers (scrubbers),
extending in layers across the length of the drum. These screens perform the
final stage of separation.
Superheater: Superheaters (SH) are meant for elevating the steam
temperature above the saturation temperature in phases; so that maximum
work can be extracted from high energy (enthalpy) steam and after expansion
in Turbine, the dryness fraction does not reach below 80%, for avoiding
Turbine blade erosion/damage and attaining maximum Turbine internal
efficiency. Steam from Boiler Drum passes through primary superheater
placed in the convective zone of the furnace, then through platen superheater
placed in the radiant zone of furnace and thereafter, through final superheater
placed in the convective zone. The superheated steam at requisite pressure and
temperature is taken out of boiler to rotate turbo-generator.
Reheater: In order to improve the cycle efficiency, HP turbine exhaust steam is
taken back to boiler to increase temperature by reheating process. The steam is
passed through Reheater, placed in between final superheater bank of tubes
& platen SH and finally taken out of boiler to extract work out of it in the IP
and LP turbine.
De-superheater (Attemperator): Though superheaters are designed to
maintain requisite steam temperature, it is necessary to use de-superheater
to control steam temperature. Feed water, generally taken before feed water
control station, is used for de-superheating steam to control its temperature at
desired level.
Drain & Vent: Major drains and vents of boiler are (i) Boiler bottom ring header
drains, (ii)
Boiler drum drains & vents, (iii) Superheater & Reheater headers drains & vents,
(iv) Desuperheater header drains & vents etc. Drains facilitate draining or hot
blow down of boiler, as and when required; while vents ensure blowing out
of air from boiler during initial lighting up as well as facilitate depressurizing
of boiler. The continuous blow down (CBD) valve facilitates reduction in

contaminant concentration in drum water and also complete draining of
drum water. The intermittent blow down (IBD) / emergency blow down
(EBD) valve helps to normalize the excess drum water level during emergency
situation.
Technical data of the Boiler
Type Radiant, Reheat, Natural circulation, Single
Drum, Balanced drift, Dry bottom, Tilting
tangential, Coal and oil fired with DIPC (Direct
Ignition of Pulverized Coal) system.
Furnace
Width 13868 mm.
Depth 10592 mm.
Volume 5240 m3
Fuel heat input per hour 106 kcal
Designed pressure 175.8 kg/cm2
Superheater Outlet pressure 155 kg/cm2
Low temperature SH (horizontally spaced) 2849 m2
(total heating surface area)
Platen SH (Pendant platen) 1097 m2
Final superheater (vertically spaced) 1543 m2
Attemperator
Type Spray
No. of stages One
Spray medium Feed water from boiler feed pump (BFP)
Reheater
Type Vertical spaced
Total H.S. area 2819 m2
Control Burner tilt & excess air
Economiser
Type Plain tube
Total H.S. area 6152 m2

BOILER AUXILIARIES
Induced draft fan (ID fan): Induced draft represents the system where air
or products of combustion are driven out after combustion at boiler furnace
by maintaining them at a progressively increasing sub atmospheric pressure.
This is achieved with the help of induced draft fan and stack. Induced draft
fan is forward curved centrifugal (radial) fan and sucks the fly-ash laden gas
of temperature around 125°C out of the furnace to throw it into stack
(chimney). The fan is connected with driving motor through hydro-coupling
or with variable frequency drive (VFD) motor to keep desired fan speed.
Technical data of the I.D.Fan (Induced Draught Fan)
No. of boiler 3
Type Radial, NDZV 31 Sidor
Medium handled Flue gas
Location Ground floor
Orientation Suction—Vertical/45 degree to Horizontal
Delivery—Bottom Horizontal.
Forced draft fan (FD fan): Forced draft represents flow of air or products
of combustion at a pressure above atmosphere. The air for combustion is
carried under forced draft conditions and the fan used for this purpose is called
Forced Draft (FD) fan. It is axial type fan and is used to take air from
atmosphere at ambient temperature to supply air for combustion, which
takes entry to boiler through wind box. In all units except Durgapur TPS
Unit #4, this fan also supplies hot /cold air to the coal mills. The output
of fan is controlled by inlet vane / blade pitch control system.
Technical data of the F.D.Fan (Forced Draught Fan)
No. of boiler 2
Type Radial, NDZV 28/Sidor
Medium handled Clean air
Orientation 45° horizontal, delivery-bottom horizontal.

Primary air fan (PA fan) or Exhauster fan: The function of primary air is
to transport pulverized coal from coal mill to the furnace, to dry coal in
coal mill and also to attain requisite pulverized coal temperature for ready
combustion at furnace. In some units like Chandrapura TPS unit 1, 2 & 3, the
exhauster fan sucks pulverized coal and air mixture from coal mill and sends
it to the furnace.
Technical data of the P.A.Fan (Primary Air Fan)
No. of boilers 3
Type Radial, NDZV 20 Herakles
Medium handled Hot air
Orientation Suction—Vertical/45 degrees to Horizontal Delivery—Bottom Horizontal.
ASH HANDLING PLANT
A large quantity of ash is, produced in steam power plants using coal. Ash
produced in about 10 to 20% of the total coal burnt in the furnace. Handling of
ash is a problem because ash coming out of the furnace is too hot, it is dusty and
irritating to handle and is accompanied by some poisonous gases. It is desirable
to quench the ash before handling due to following reasons: 1. Quenching reduces
the temperature of ash. 2. It reduces the corrosive action of ash. 3. Ash forms
clinkers by fusing in large lumps and by quenching clinkers will disintegrate. 4.
Quenching reduces the dust accompanying the ash. Fly ash is collected with an
electrostatic precipitator (ESP)

ELECTROSTATIC PRECIPITATOR (ESP)
The principal components of an ESP are 2 sets of electrodes insulated from each
other. First set of rows are electrically grounded vertical plates called collecting
electrodes while the second set consists of corrugated wires called discharge
electrodes.
The above figure shows the operation of an ESP. the negatively charged
fly ash particles are driven towards the collecting plate and the positive ions travel
to the negatively charged wire electrodes. Collected particulate matter is removed
from the collecting plates by a mechanical hammer scrapping system.
An electrostatic precipitator (ESP) is an device that removes dust particles from
a flowing gas (such as air) using the force of an induced electrostatic attraction
(i.e, like charges repel; unlike charges attract) Electrostatic precipitators are
highly efficient filtration devices that allow the flow of gases through the device,
and can easily remove fine particulate matter such as dust and smoke from the air
stream.
COMPONENTS USED IN ELECTROSTATIC PRECIPITATOR

Control cabinet Control cabinet is used to interconnect the 3φ ac supply and
transformer through wires. Transformer is used to step up or step down the
voltage as per the design of Electrostatic precipitator. Rectifier is used to convert
the given ac supply into dc supply. Hooper is used to store the dust particles and
ash content coming out from the Electrostatic precipitator.
Electrodes: - Based on DC current flow terminals electrodes can be divided as
below: -
Discharge electrode: - Electrodes wire which carries negatively charged high
voltage (between 20 to 80KV) act as discharge or emitting electrodes.
Collector electrode: - Electrode wire which carries positively charged high
voltage act as collecting electrodes. Collector electrodes Discharge electrode
WORKING OF ELECTROSTATIC PRECIPITATOR
Several things happen very rapidly (in a matter of a millisecond) in the small area
around the discharge electrode. Electric field is emerged due to dc terminal
arrangement. The applied (-) voltage in discharge electrode is increased until it
produces a corona discharge, which can be seen as a luminous blue glow around
the discharge Electrode. Due to the formation of corona discharge, free electrons
are emitted with high velocity from discharge electrode. This fast moving free
electrons strikes the gas molecule thus emission of free electron from gas
molecules takes place. The positive ion molecule move towards discharge
electrode by electrostatic attraction As a result using gas molecule more free
electrons are emitted near the discharge electrode. Stage - 1
Stage - 2 as the electrons leave the strong electrical field area around the
discharge electrode, they start slowing down. This free electron again strikes the
gas molecule but this time they are captured by gas molecule and became
negatively charged ion. As the gas molecule are negatively ionized they move
towards the (+) electrode (i.e., collector electrode). This negative gas ion fills the
space of Dust particle and becoming negatively charged particle. This particle are
captured by collector electrode.

STEAM TURBINE
A steam turbine is a rotary mechanical device which extracts kinetic energy from
a fluid flow and converts it into useful work. A turbine consists of at least one
moving part called the rotor assembly, which is a shaft with blades attached.
Moving fluid acts on the blades so that they move and impart rotational energy
to the rotor. Steam turbines can be classified into mainly two types: Reaction type
and Impulse Type. A reaction turbine is one with rotating blades curved and
arranged so as to develop torque from gradual decrease of steam pressure from
inlet to exhaust, while impulse turbine is one which is driven by high velocity
steam and imparts constant pressure energy steam at the output of the blades.
Majority of the high rated steam turbines used in thermal power stations are
reaction type, following Newton’s 3rd
law of motion to deliver pressure as well
as kinetic energy to the steam output from the blades. Also, it is to be noted that
most steam turbines comprise of a number of stages (HP, IP and LP) for
expansion of the steam before being delivered to the condenser; because each
stage only extracts a bit of the work from the incoming steam. The stages are
designed to work with one another in unison so that each stage can extract a bit
of work from the steam exhausted from the stage upstream of it. This also helps
to extend the range of pressure-drops from where work can be extracted. If the
outlet pressure from the turbine blades is equal to the normal ambient pressure, it
implies that all useful steam velocity has been utilized to rotate the rotor of the
generator.

210 MW (KWU) steam turbine (Mejia TPS U # 1, 2, 3 & 4):
HP turbine inlet steam: 147 kg/cm2
& 5370
C. Steam entry to HP turbine through
two combined main stop & control valves and to IP turbine through two combined
reheat stop & control valves. Reheated steam pressure and temperature: 34.5
kg/cm2
& 537 0
C.210 MW KWU turbine is a tandem compounded, three
cylinders, single reheat, condensing turbine provided entirely with reaction
blading.
Number of stages: HPT-25 stages, IPT – double flow with 20 reaction stages per
flow and LPT – double flow with 8 stages per flow. Six steam extractions for
feed/condensate water heating have been taken from HPT exhaust & 11th
stages
of IPT for high pressure heaters, from IPT exhaust for de-aerator and from 3rd
,
5th
, & 7th
stages of LPT for low pressure heaters. The individual turbine rotors
and the generator rotor are connected by rigid couplings.
250 MW (KWU) steam turbine (Mejia TPS U # 5&6)
HP turbine inlet steam: 147.10 kg/cm2
& 537 0
C. Steam entry to HP turbine
through two combined main stop & control valves and to IP turbine through two
combined reheat stop and control valves. Reheated steam pressure and
temperature: 34.95 kg/cm2 and 537 degree. 250 MW KWU turbine is a tandem
compounded three cylinders single reheat condensing turbine provided entirely
with reaction blading.
Number of stages: HPT single flow with 25 stages, IPT- single flow with 17
stages and LPT double flow with 8 stages per flow. Six steam extractions for feed
/condensate water heating have been taken from HPT exhaust &11th
stage of IPT
for high pressure heaters, from IPT exhaust for de-aerator and from 3rd
, 5th
and
6th
stages of LPT for low pressure heaters. The
Individual turbine rotors and the generator, rotor are connected by rigid
couplings.
500 MW (KWU) steam turbine (Mejia TPS U#7&8)
HP turbine inlet steam: 170 kg/cm2 and 535deg. Steam entry to HP turbine
through two combined stop and control values and IP turbine through four
combined reheat stop and control valves. Reheated steam pressure and
temperature: 34.95 kg/cm2 &535 e.g. 500MW KWU turbine is tandem
compounded, three cylinders, single reheat condensing turbine provided entirely
with reaction blading.

COOLING TOWER
A cooling tower is a heat rejection device that rejects waste heat to
the atmosphere through the cooling of a water stream to a lower temperature.
Cooling towers may either use the evaporation of water to remove process heat.
Cooling towers cool the warm water discharged from the condenser and feed the
cooled water back to the condenser. They thus reduce the cooling water demand
in the power plants. Cooling towers could be mechanically draught (Induced and
Forced) or natural draught. In M.T.P.S the cooling towers are induced draught
type for units 1-6 and natural draught for units 7&8.
Natural draught — Utilizes buoyancy via a tall chimney. Warm, moist air
naturally rises due to the density differential compared to the dry, cooler outside
air. Warm moist air is less dense than drier air at the same pressure. This moist
air buoyancy produces an upwards current of air through the tower.
Induced draught — a mechanical draft tower with a fan at the discharge (at the
top) which pulls air up through the tower. The fan induces hot moist air out the
discharge. This produces low entering and high exiting air velocities, reducing
the possibility of recirculation in which discharged air flows back into the air
intake. This fan/fin arrangement is also known as draw-through.

CHIMNEY
A chimney is a structure that provides ventilation for hot flue gases or smoke
from a boiler, Chimneys are typically vertical, or as near as possible to vertical,
to ensure that the gases flow smoothly, drawing air into the combustion in what
is known as the stack, or chimney effect. The space inside a chimney is called a
flue. The height of a chimney influences its ability to transfer flue gases to the
external environment via stack effect. Additionally, the dispersion of pollutants
at higher altitudes can reduce their impact on the immediate surroundings. In the
case of chemically aggressive output, a sufficiently tall chimney can allow for
partial or complete self-neutralization of airborne chemicals before they reach
ground level. The dispersion of pollutants over a greater area can reduce their
concentrations and facilitate compliance with regulatory limits.
Chimney No For Unit N0 of Chute Height (metre)
1 1,2,3 3 220
2 4 1 220
3 5,6 1 220
4 7,8 2 279

ELECTRICAL OPERATION
Generator:
The turbo generator is a 3phase, Horizontal mounted, 2 pole cylindrical rotor
type machine driven by a directly coupled steam turbine at 300 rpm. The
machine is manufactured as per design of M/S ELECTROSILA USSR and
broadly conforms to National & International Electro-technical commission
standard. The stator winding including terminal bushing is directly cooled by
water while rotor winding, core iron and all other parts are cooled directly by
H2.
The windings are insulated for class B temperature rise and are given anti
corona treatment. To prevent escape of H2 from generator casing, ring type H2
seals are provided at either end of the machine. A generator consists of the
following main components and associated systems:
Stator: The stator embodies the stator core, stator winding, H2 cooler and
provides a gas tight enclosure for H2 gas. The stator body is designed to
withstand internal pressure of explosion of H2-air mixture without any residual
deformation. The stator body is hydraulic pressure tested during manufacture at
a pressure more than twice the operating H2 pressure. The stator comprise of ac
inner & outer frame. The outer frames is a rigid fabricated structure of welded
steel plates capable of bearing the pressure due to minor explosion of H2 within
the casing. Within this cylindrical barrel girder built circular and axial ribs
forms a fixed cage. These ribs divide the yoke into annular components through
which cooling gas flows into radial ducts in the stator core and exchanges heat
in the H2 gas coolers housed horizontally parallel to the rotor shaft in the frame.

The inner cage is usually fixed to the yoke by an arrangement of springs to
dampen vibration. The stator body shall be provided with a man-hole with
suitable sealing arrangement located at the middle of the stator body at lower
half to facilitate inside inspection, terminal connection etc. Rigid end shields
close the stator ends and support the fan shields and shaft seals. Detachable type
trunnion footplates are provided for mounting the stator on foundation.
Stator Core: The stator core is built up for segmental punching of high
permeability, low loss cold rolled silicon sheet steel varnish insulated on both
sides which are assembled in an interleaved manner on spring core bars. Cold
rolled silicon steel is used to reduce heating due to eddy current loss. The core
consists of several packets separated by steel spacers for radial cooling of the
core by H2. The spring core bars ensure effective damping of the double
frequency core vibrations going to the foundation and help in reducing the noise
level of the assembly. To ensure a tight & monolithic core, pressing of the
punching is effected in several stages and when completely built, the core is
held in pressed condition by means of heavy magnetic steel press rings which
are bolted to the ends of core bars. Addition support is provided to the teeth
portion by means of non-magnetic fingers held between the core and the press
rings. The press rings are tapered on the face towards the core so that an even
pressure is exerted over the end surface of the core when core bars are
tightened. Copper damper screens provided between the end packets and press
rings reduce the end zone heating. The core and packets on both sides are made
monolithic by bending together under separately epoxy varnish coated segments
which fully ensures and minimizes the vibration likely to be produced on core
ends, especially teeth due to end leakage flux.
Stator Winding: The stator has a 3 phase double layer short corded bar type
lap winding having two parallel paths. The stator winding is designed for
connection in double star with three phase & six neutral terminal for providing
inter turn short circuit (87GI) protection. Each coil side consists of glass-
insulated solid and hallows conductors with cooling water passing through the
later. The elementary conductors are transposed in the slot portion of the
winding to minimize the eddy losses. The winding bars are insulated with mica
thermo-setting insulation tape which consists of a flexible mica foil, fully
saturated with a synthetic resin having excellent electrical properties and
bounded to a even glass fabric in order to increases the tensile strength. The
stator winding insulated conforms to class B. Adequate protection is provided to
avoid corona and other surface discharge. The overhang portion of the coils is
securely lashed with Terylene cord to bondage rings and the special brackets of

glass terminals and nonmagnetic steel which are in turn fixed to the core press
rings.
Terminal Bushing: Water-cooled terminal bushings are housed in the lower
part of the stator on the slip ring side. Protection insulators are provided to
insulate the terminal bars from the stator body. Effective sealing is provided
between the terminal bushings and stator body to avoid any possibility of
leakage of H2. Terminal bushings are housed inside a chamber made of non-
magnetic steel plates. Three phase terminals and six neutral terminals are
brought out to facilitate external connections. The terminal plates where the
external connections are made to the bus ducts are Silver-plated.
Bus Duct The bus duct connects the generator outgoing terminals to the
generator transformer (GT) with tap-off through disconnecting links for unit
auxiliary transformers (UAT). Bus duct is made of aluminium alloy. Bust duct
are of isolated phase design and consists of conductors, insulators, enclosures
etc. Ring types CT are provided in the enclosure for measurement and
protection requirements.
Rotor Shaft: The generator rotor forms the rotating magnetic poles. The rotor is
of cylindrical type, the shaft and body being forged in one-piece form chromium
nickel molybdenum and vanadium steel. Slots are machined on the outer surface
to incorporate windings. Holes are also drilled for ventilation purposes. Prior to
machining, a series of comprehensive ultrasonic examinations and other tests are
carried out on rotor body and shaft portions to ensure absence of any internal
defects. The rotor with all the components assembled is dynamically balanced to
a high degree of accuracy and subjected to 20 % over speeding for 2 mints
ensuring mechanical strength.
Rotor Winding: The rotor winding consists of coils made from hand drawn (0.03
to 1.0 %) silver copper with bonded insulation. The winding is held in position
against centrifugal forces by duralumin wedges in the slot portion and by non-
magnetic steel retaining rings machined from high strength non-magnetic alloy
steel forgings in the overhang portion. Gap pick up system is employed for direct
H2 cooling of rotor windings. Several groups of ventilation ducts are milled on
the sides of the rotor coils for gas passes. The rotor slot wedges are of special
profile with elliptical holes milled in to match the ventilation ducts on the winding
stacks. The main slot insulation is in the form of U profile made of glass cloth
impregnated with epoxy resin. The U profile facilitates easy flow of gas from one
side to the other side of the coil stack. The inter turn insulation consists of layer
of epoxy pregnant glass cloth glared to the bottom of each conductor and
consolidated in regulated condition of temperature and pressure. The end

windings are packed with blocks of glass laminates to separates and support the
coils and to restrict their movement under stress due to thermal and rotational
forces. The end windings are insulated from retaining rings with the help of glass
epoxy mould segments. Copper segmental type silver-plated damper windings
are provided in the end zones of the rotor in order to prevent over heating of
retaining asymmetrical and asynchronous operation.
Cooling Fan: Two propeller type-cooling fans are shaft mounted at both ends of
the rotor for forced circulation H2 gas inside the generator casing. Fan hubs are
made from alloy steel forging and are hot fitted on the fan hub with the help of
high strength alloy steel conical pins. These fan blades are easily removable from
the hub. Fan shields are provided to guide the gas flow. Fan shields are fixed to
the end shields.
Retaining Rings: The overhang portions of the field winding are held in position
against centrifugal forces by retaining rings machined from high strength, heat
treated non-magnetic alloy steel forgings. The retaining rings are of floating type
shrunk on the rotor body. The locking nuts also machined from high strength
nonmagnetic alloy steel forgings are screwed on to retaining rings to prevent axial
movement. Ring mounted at the end of the retaining rings support and prevent
the movement of rotor winding in axial direction due to thermal stress.
Slip Ring: The slip rings assembly is made up of helically grooved alloy steel
rings shrunk on the rotor shaft and insulated from it. For convenience in assembly
both the ring mounted on a single common steel brush, which has an insulating
jacket of epoxy glass pre mounted on it. The complete brush with slip rings is
shrunk on the rotor shaft. The slip rings are provided with inclined holes for self-
ventilation. A helical groove is machined in the surface of the slip rings to prevent
air building up under the brushes and adversely affecting CT. The slip rings are
connected to the field winding through semi-flexible copper leads and current
carrying bolts placed radially and two semi-circular insulated hard copper bars,
placed in the central bore of the rotor.
Generator bearings: Generator bearings are of pedestal type with spherical
seating to allow self-alignment and are supported on a separate pedestal on slip
ring side and in the LP casing on the turbine side. The pedestal is massive steel
casting providing high rigidity. Bearing bush is made up of cast steel lined with
high quality white metal. Oil under pressure is supplied to the bearing through a
diaphragm, which is preselected to regulate the flow so as to get the temperature
rise within the limits. Oil catcher & deflectors are provided to check the axial
leakage of oil. Vent pipe is provided on the bearing cover connecting the inside
chamber for escape of H2 which may come out along with seal oil and get

accumulate in the bearing cover. For checking the flow of oil, check windows are
provided in drain pipes. To prevent shaft currents slip ring side bearing and
connecting pipes are insulated from earth.
Brush Gear: Brush gear is provided on the extended part of bearing pedestal on
the slip ring side for feeding current to rotor winding. Brush holders staggering
of the brushes along with width of slip rings to avoid non-uniform contact
pressure and the brush pressure (0.9 – 1.0 kg /cm2) can be adjusted individually.
The brushes are provided on upper 2/3 peripheries of the slip rings. A fabricated
hood covers the brush gear assembly to protect it from any mechanical damage.
Each brush gear limb is provided with 56 brushes of 22x30x60. The design of
brush gear permits replacement of the brushes during normal running conditions.
Cooling System: The generator losses (i.e. sum of copper losses of stator & rotor
winding and hysteresis & eddy current losses) are dissipated as heat through
stator and rotor bodies. This heat should be taken off for safe operation of the
generator. Forced ventilation and total enclosures are necessary to deal with the
large-scale losses and high rating per unit volume.
Sealing System: TG shaft seals are supplied with pressurized oil to prevent
escape of H2 at the shaft from where it comes out of the stator and ingress of air
in the generator.
Excitation System
With increase in generator capacity and complexity of interconnection in power
system, improved techniques in generator excitation have been developed with
the aim to achieve higher capacity, ideal rate of response, simplicity, reliability,
accuracy and sensitivity. In earlier designs of excitation system:
 Exciters were commutator type and self-excited.
 Exciters were shaft driven and motor driven rotating machine.
 Voltage regulators included magnetic or rotating amplifiers or combination
of both.
 Manual control was by means of a rheostat.

Next generation of excitation system:
 Use of semiconductors for rectification.
 AC (automatic) voltage regulators with transistor preamplifiers and
thyristors.
 New concepts of manual control.
 Elimination of commutator.
New physical arrangements and new maintenance procedure. Present day
excitation system:
 Very high values of excitation suitable for unit capacities as high as 500
MW or even more.
 Use high HF AC exciters as source of power.
 Higher stability limit and excellent performance during transient and fault
condition.
 Elimination of carbon brushes in brush less excitation system.
Excitation system can be categorized and subdivided into the followings:
DC Excitation Systems: Pilot-Main Exciter excitation DC exciters are basically
rotating shunt / compound wound machines driven from the main generator shaft
either be means of direct coupling or through reducing gear. Generation of
excitation power is done in two stages, firstly a relatively small permanent magnet
pilot exciter generates voltage to supply excitation power for the main exciter in
turn supplies field current to the main generator. Generator output voltage is
measured with the help of PT’s and fed to the Automatic Voltage Regulator
(AVR). AVR operates in the output of pilot exciter to modify the field current to
the main exciter with help of a monitoring field rheostat.
Rotating Amplifier excitation in some old higher rated (above 25 MW) machines
with dc excitation system rotating amplifier (amplidyne) is usually used. The
amplidyne generator is connected in series with the exciter field and can produce
current with either polarity to boost or buck the exciter field current. The
amplidyne can be switched out of the circuit and the voltage controlled manually
by the exciter field rheostat. Current and voltage signal taken from the output of
generator are compared to the voltage regulator reference. If a change in the
excitation is required current will flow into the amplidyne field to cause the
amplidyne output to the boost or buck exciter field current. With the use of
amplidyne regulator the overall response of the system can be increased
compared to previous one. As the rating of the generator increased DC excitation

system presented serious problem because of commutation problem, frequent
maintenance for the commutator and brush gear assembly, higher cost etc and
gradually AC excitation systems which are free from these constraints gained
popularity.
AC Excitation Systems: High Frequency excitation. This system was developed
to avoid commutator and brush gear assembly. The main exciter (HFEX) is an
inductor type generator, which has 3phase AC winding and 4 field windings on
the stator and no winding on the rotor. These 4 windings are series winding, boost
winding, buck winding and manual winding. In this system, a shaft driven pilot
exciter, which has a rotating permanent magnet field and a stationary armature
feeds DC control current to the boost and buck field of the main high frequency
AC exciter through controlled rectifiers. The HF output of the stationary armature
is rectified by stationary diode and fed through series winding via slip rings to the
field of main generator. The manual winding is usually kept open. Excitation of
the HFEX is varied by means of AVR having a power magnetic amplifier at its
output stage or by means of a thyristor controlled AVR set. A response ratio of
this system is about 2.
Brush less excitation Supply of high current by means of slip ring involves
operational problem. These problems are eliminated in brush less excitation
system, which consists of AC main exciter, PMG, rotating diodes all, mounted
on the TG shaft and static AVR. Field of the PMG, which is permanent salient
pole magnet rotates along with generator shaft and generates permanent voltage
at the stator winding. This output of the PMG is connected to the thyristor located
in AVR panel. The controlled DC output from AVR panel is connected to the
stationary field of the main exciter. The output from the rotating armature of main
exciter is connected to the diodes placed along with rotating shaft. The DC output
from rotating diodes is connected to the field winding of the generator. The
response ratio of this system is above 2.
Static excitation In order to maintain system stability it is necessary to have fast
excitation system for large generator which means the field current must be
adjusted extremely fast to changing operational conditions, besides maintaining
the field current and steady state stability limits. Therefore, static excitation
system (SEE) is preferred to conventional excitation system. In MTPS, this type
of excitation system is used. In this system, the AC power is tapped off from the
generator terminal, stepped down and rectified by fully controlled thyristor
bridges and then fed to the generator field, thereby controlling the generator
output voltage. A high control speed is achieved by using an inertia free control
and power electronics system. Any deviation in the generator terminal voltage is

sensed by an error detector and causes the voltage regulator to advance or retard
the firing angle of the thyristor thereby controlling the field excitation of the
generator. The response ratio of this system is 3 to 5. This equipment controls the
generator terminal voltage and hence the reactive load flow by adjusting the
excitation current. The rotating exciter is dispensed with and the silicon-
controlled rectifiers (SCR) are used which directly feed to the field of generator.
The SEE consists of (i) Excitation transformer (ii) SCR output stage (iii)
Excitation start up and field discharge equipment (iv)Control and power
electronics system (v) Power supply (vi) Protections
TECHNICAL SPECIFICATIONS
Main parameters
Rated kW capacity 210000 kW
Rated kVA capacity 247000 kVA
Rated terminal voltage 15750 V
Rated power factor 0.85 lag
Rated stator current 9050 amps
Rated speed 3000 RPM
Rated frequency 50 Hz
Efficiency at rated power output & power factor 98.55%
Power factor short circuit ratio 0.49
Temperature rating
Class of insulation of generator windings Class 'B'
Temperature of cooling water (maximum) 37°C
Temperature of cooling Hydrogen (maximum) 44°C
Temperature of cooling distilate (maximum) 45°C
Maximum temperature of stator core 105°C
Maximum temperature of stator winding 75°C
Maximum temperature of rotor winding 115°C
Other particulars
Critical speed of rotor (calculated) 1370/3400 RPM
Fly wheel moment of rotor 21.1 T-M
Ratio of short circuit torque to full load torque 8

Quantity of oil required for cooling per bearing 300 litre/min.
Oil pressure for lubrication of bearings 0.3-0.5 kg/cm2
Quantity of oil required for both the shaft seals 7.7 litres/min.
Rated pressure of the shaft seal oil (gauge) 5 kg/cm2
Quantity of water required for gas coolers 350 m3
/hr.
Maximum allowable water pressure in gas
coolers
3 kg/cm2
Quantity of distillate for cooling stator winding 27 m3
/hr.
Max. distillate pressure at inlet to stator
winding
3.3 kg/cm2
Average qty of Hydrogen required for makeup 15 m3
per day
% Purity of Hydrogen inside the machine 97% min
Max allowable moisture content inside the body 1.5 g/m3
Weights of different parts
Heaviest weight (weight of stator) (kg.) 170000
Bearing with brush rocker & foundation plate
(kg)
9300
Rotor (kg.) 42000
Gas cooler (kg.) 1415
Terminal bushing (kg.) 85
Total weight of generator (kg.) 239000
TRANSFORMERS
The electricity thus produced by the generator then goes to the generating transformer where
the voltage is increased for transmission of electricity with minimized copper losses. In
general a transformer consists of primary and secondary windings which are insulated from
each other by varnish. In M.T.P.S. all are either oil cooled or air cooled. Some of the
transformer accessories are: 1. Conservator tank 2. Buccholz relay 3. Fans for cooling 4.
Lightning arrestors 5. Transformer bushings 6. Breather and silica gel.
Generating transformer #1, 2, 3, 4
MVA: 150/200/250 (H.V.) MVA: 150/200/250 (L.V.) Volts at no load: 240000
(H.V.) Volts at no load: 15750 (L.V.) Ampere line value: 361/482/602 (H.V.) Ampere line
value: 5505/7340/9175 (L.V.) Phase-3 frequency: 50 Hz. Mass of core and windings:

139000 kg. Mass of oil: 38070 kg. Mass of heaviest package: 164000 kg. Connection:
YNd1 connection.
Generating transformer#5 and 6
MVA: 189/252/315 (H.V.) MVA: 189/252/315 (L.V.) Volts at no load: 16.5kV
(L.V.) Volts at no load: 240kV (H.V.) Ampere line value: 757.57 (H.V.) Ampere line
value: 11022.14 (L.V.) Phase-3 frequency: 50 Hz. Mass of core and windings: 155000 kg.
Mass of oil: 53070 kg. Mass of heaviest package: 18000 kg. Connection: YNd1 connection.
Specifications of Generator Transformer (GT) at Unit #7
Type of cooling ONAN/ONAF/OFAF
Rating HV (MVA) 120/160/200
Rating LV (MVA) 120/160/200
No load voltage HV (kV) 242.494
No load voltage LV (kV) 21
Line current HV (amps) 824.79
Line current LV (amps) 9523.8
Temperature rise oil (°C) 40 (Over ambient of 50°C)
Temperature rise winding (°C) 45 (Over ambient of 50°C)
Phase 3

Frequency (Hz) 50
Connection symbol YNd11
Impedance volt at 200 MVA Base HV Position on 5/LV (nor tap) – 12% to
15%
HV Position on 1/LV (max tap) – 12% to
15%
HV Position on 9/LV (min tap) – 12% to
15%
Insulation level (HV) SL 1050 LI 1300 – AC 38
Insulation level (LV) LI 125 – AC 50
Core & Winding (kg) 153530
Weight of oil (kg) 48910
Total weight (kg) 257500
Oil quantity (litre) 56220
Transport weight (kg) 174900
Untanking weight (kg) 13790
Vector Diagram
AUXILIARY TRANSFORMRERS
Station Service Transformers:
Normal source to the station auxiliaries and standby source to the unit auxiliaries
during start up and after tripping of the unit is station auxiliary transformer.
Quantity of station service transformers and their capacity depends upon
the unit sizes and nos. Each station supply transformer shall be one
hundred percent standby of the other. Station service transformers shall cater
to the simultaneous load demand due to start up power requirements for the
largest unit, power requirement for the station auxiliaries required for running

the station and power requirement for the unit auxiliaries of a running
unit in the event of outage of the unit source of supply. The no. and
approximate capacity of the SST depending upon the no. and MW rating of the
TG sets are indicated below.
Specifications of Station Service Transformer (SST) at Unit 7 and 8
Type of cooling ONAF/ONAN
Rating HV (MVA) 16/12.50
Rating LV (MVA) 16/12.50
No load voltage HV (kV) 11
No load voltage LV (kV) 3.45
Line current HV (amps) 839.78/656.08
Line current LV (amps) 2677.57/2091.85
Temperature rise oil (°C) 40
Temperature rise winding (°C) 45
Phase 3
Frequency (Hz) 50
Connection symbol Dyn1
Impedance volts % HV-LV 25%
Unit Auxiliary Transformer:
The normal source of HV Power to unit auxiliaries is unit auxiliary transformer.
The sizing of the UAT is usually based on the total connected capacity of running

unit auxiliaries i.e., excluding the stand by drives. It is safe and desirable to
provide about 20% excess capacity than calculated. The no. and recommended
MVA rating of unit auxiliary transformers are as shown in the above table: The
UATs shall have Ddo(ungrounded system) or Dy1 (for grounded system)
connection with on load tap changer to provide +10 % variation in steps of
1.25 %. Usual cooling arrangement to unit auxiliary transformers are ONAN.
Radiators are usually divided in two equal halves.
Specification
Unit auxiliary transformer #1, 2, 3
MVA: 12.5/16 Manufacturer: Atlanta Electricals
Volts at no load: 15750 (H.V.) Volts at no load: 6900 (L.V.)
Ampere line value: 458.2/586.5 (H.V.) Ampere line value: 1045.9/1338.8 (L.V.)
Phase-3 frequency: 50 Hz.
Mass of core and windings: 14300kg.
Mass of oil: 8600kg. Mass of heaviest package: 25000kg. Total weight: 30,500
kg.
Unit auxiliary transformer #5 & 6
Type of cooling: ONAN/ONAF (oil natural/ oil natural air force)
Rating (H.V.): 20/16 MVA Rating (L.V.): 20/16 MVA No load voltage: 13.5
kV (H.V.) No load voltage: 6.9 kV (L.V.) Line current: 1673.479/1336.783 amp.
Temperature rise of winding: 55*C
Insulation level: 931 KVI 38kV rms (H.V.) 60kVI 20kV rms (L.V.)
Specifications of Unit Auxiliary Transformer (UAT) at Unit #7

Type of cooling ONAN/ONAF
Rating HV (MVA) 45/36
Rating LV (MVA) 45/36
No load voltage HV (kV) 21
No load voltage LV (kV) 11.5
Line current HV (amps) 1238.64
Line current LV (amps) 2261.87
Temperature rise oil (°C) 40 (Over ambient of 50°C)
Temperature rise winding (°C) 45 (Over ambient of 50°C)
Phase 3
Frequency (Hz) 50
Connection symbol Dyn1
Impedance volt at 45 MVA Base HV Position on 7/LV (nor tap) – 11.5%
HV Position on 1/LV (max tap) – 10%
to 13%
HV Position on 17/LV (min tap) – 10%
to 13%
Insulation level (high voltage) L1 125 – AC 50
Insulation level (low voltage) L1 75 – AC 28
Core & winding (kg) 40065
Weight of Oil (kg) 25765
Total weight (kg) 85265
Transport weight (kg) 50000
Un tanking weight (kg) 41000

CONTROL ROOM UNIT:
The above figure shows the power line diagram in the control room. It clearly shows how the
electric power generated by the generator is transmitted through the generating transformers
into the bus and the distribution of power by the unit auxiliary transformers.
SWITCHYARD SECTION
Introduction:
In a switchyard, special care should be taken to prevent any type of mal-
operation, which may cause severe disturbance to the entire grid to which it is
connected, and hazard to the operating personnel. Before any normalization
operation is ensured that all the PWC related to that bay and associated main
bus are cleared and safety grounding have been removed. Prior to clearance for
any planned shutdown of any Transmission Line and main bus shall be obtained
from CLD, Mython. Any operation related to Transmission Line shall be in co-
ordination with the other end. DC supply healthy indication shall always glow.
SF6 gas pr., N2 gas pr. and oil pr. of 220, 33 KV SF6 breakers should be checked
in regular interval.

220 KV Isolator Operation:
 Never attempt to open or close any isolator if the associated breaker is
ON condition.
 In 220 KV switchyard, simultaneous closing of Iso#1 (for MB#1) and
Iso#2 (for MB#2) isolators are not allowed except bus tie in service.
 After closure of isolator check locally for complete movement and
perfect twisting of the blade.
 In case the isolators are operated from the switchyard control panel
(Remote operation), the following points should be done:
a) Check that isolator selection switch in local isolator panel is in
‘Remote’ position and operating motor supply is ON condition.
Operation of the corresponding VAJC relay (i.e. CT switching relay)
(for Iso#1 89AX, Iso#2 89BX and Iso#4 89CX) set / reset must be
ensured after each operation of the isolators before proceeding
the next step of operation.
b) During change-over of load from one bus to another and diversion
through the Transfer bus, all the bus differential cut off switch shall
be kept in the OUT position, to be put into IN position again after
satisfactory completion of the entire operation.
 In case the isolators are operated locally in the switchyard (either
electrically or manually), the following points should be done: -
(a) Check that isolator selection switch in local isolator panel is in ‘Local’
position and operating motor supply is ON condition.
(b) The control switch of respective isolators will have to be operated
sequentially for operation of the VAJC relay of the respective bays. Precisely,
this will correspond to the following:
 Isolator close impulse to be given before local closing of the isolators.
The VAJC relay shall operate.
 Isolator open impulse to be given before local opening of the
isolators. The VAJC relay shall reset.

(c) With bus differential protection in service, during changeover of load from
one MB to another and diversion through TB the following operating sequence
shall be adopted.
 The bus differentials cut off switch of Main zone and check zone shall
be changed over to OUT position.
For change over from MB1 to MB2 the Iso#2 control switch for the
concerned bay shall be given close impulse for operation of VAJC relay.
After ensuring operation of the VAJC relay, Iso#2 shall be closed locally.
Iso#1 shall be opened locally thereafter. Finally the control switch for Iso#1
shall be given open impulse for reset of the VAJC relay to be ensured again
by inspection. The corresponding bus differential cut off switch shall be put
to IN position.
 Similar sequence shall be followed for changeover of load from
MB2 to MB1.
 For diversion through TB all the bus differential cut off switch shall
be put to OUT position, them the concerned TB isolator (Iso#4) control
switch shall be given close impulse for operation of VAJC relay followed by
local closing of the Iso#4. Thereafter the concerned bus isolator control
switch (for MB#1 & MB#2) of bus coupler bay shall be given close impulse
for operation of the VAJC relay followed by local closing of the isolator. TB
side isolator of the bus coupler bay shall then be closed and the NIT switch
shall be placed to INTER position and selection switch shall be placed to
Switchyard for Line, Transformer & U#1 for unit 1 & U#2 for unit 2 & U#3
for unit 3 position. The bus coupler CB shall thereafter be closed. The
controlling CB of the bay, to be diverted, shall then be made off, and its
concerned bus side isolators shall be opened locally. Finally the related
control switch of Iso#1 or Iso#2 shall be given an open impulse for reset of
the VAJC relay. The NIT switch shall then be put to TRANSFER position
and the bus differential cut off switch shall be put back to IN position.
 During diversion through TB involving operation of either or both the
TB section isolators (High level isolator), the operation of corresponding
VAJC relay shall be similarly carried out and checked. The VAJC relay
related to the bus section isolator (B/C I & B/C II) are located in the relay
panel of B/C.
The basic components of a switchyard are as follows:
1. Circuit breaker:
A circuit breaker is an equipment that breaks a circuit either manually or
automatically under all conditions at no load, full load or short circuit. Oil circuit

breakers, vacuum circuit breakers and SF6 circuit breakers are a few types of
circuit breakers.
2. Isolator:
Isolators are switches which isolate the circuit at times and thus serve the purpose
of protection during off load operation.
3. Current Transformer :
These transformers used serve the purpose of protection and metering. Generally
the same transformer can be used as a current or potential transformer depending
on the type of connection with the main circuit that is series or parallel
respectively. In electrical system it is necessary to
a) Read current and power factor
b) Meter power consumption.
c) Detect abnormalities and feed impulse to protective devices.
4. Potential transformers:
In any electrical power system it is necessary to - . a) Monitor voltage and power
factor, b) Meter power consumption, c) Feed power to control and indication
circuit and d) Detect abnormalities (i.e. under/over voltage, direction of power
flow etc.) and feed impulse to protective device/alarm circuit. Standard relay and

metering equipment does not permit them to be connected directly to the high
voltage system. Potential transformers therefore play a key role by performing
the following functions. a) Electrically isolating the instruments and relays from
HV side. b) By transferring voltage from higher values to proportional
standardized lower values.
5. POWER TRANSFORMER:
The use of power transformer in a switchyard is to change the voltage level. At
the sending and usually step up transformers are used to evacuate power at
transmission voltage level. On the other hand at the receiving end step down
transformers are installed to match the voltage to sub transmission or distribution
level. In many switchyards autotransformers are used widely for interconnecting
two switchyards with different voltage level (such as 132 and 220 KV)
6. Insulator:
The live equipment are mounted over the steel structures or suspended from
gantries with sufficient insulation in between them. In outdoor use electrical
porcelain insulators are most widely used. Following two types of insulators are
used in switchyard. a. Pedestal type b. Disc type Pedestal type insulators are used
on steel structures for rigid supporting of the pipe bus bars, for holding the blade
and the fixed contacts of the isolators.
Electric power is generated by the generator which is circulated to the main bus
1 or 2 and accordingly the respective isolator is closed. In case of any fault in the
circuit breaker the power from the generator goes via the transfer bus into the
main bus by means of the bus coupler. A bus tie represents the connection
between the two main buses. Two 80MVA transformers draw power from the
main buses and transfer the voltage to 33kV and the power goes to 33kV
switchyard. A station service transformer supplies power to the auxiliary load.
The electric power after voltage transformation to 33kV by 80MVA transformers
goes to the main bus of the 33kV switchyard from where power is fed to various
industries and other nearby stations. There are two earthing transformers in the

yard. From the bus the power is fed to two 5MVA transformers which step down
the voltage level to 11kV and is thus distributed to the locality.
THE TYPE OF RELAYS USED IN MTPS FOR PROTECTION OF
POWER SYSTEM COMPONENTS
• Auxiliary relay for isolations • Fail accept relay • Directional over current relay
• Master trip relay • Multi relay for generator function • Supervision relay •
Instantaneous relay • Bus bar trip relay • Lock out relay • Numerical LBB
protection relay • Transformer differential protection relay • Circulating
differential protection relay • Contact multi-relay • Auxiliary relay • Trip circuit
R-Phase relay • EUS section relay • DC fail accept relay • Trip circuit R-phase
super relay Y-phase B-phase • LBB protection relay.
SWITCHGEAR
HV Switchgears:
Indoor metal clad draw out type switchgears with associated protective and
control equipment are employed (fig. 2). Air break, Air Blast circuit breakers
and Minimum Oil circuit breakers could still be found in some very old
stations. Present trend is to use SF6or vacuum circuit breakers. SF6 and vacuum
circuit breakers requires smaller size panels and thereby reasonable amount of
space is saved. Fig. 2: General arrangement of 6.6 KV switchgear panels The
main bus bars of the switchgears are most commonly made up of high
conductivity aluminium or aluminium alloy with rectangular cross section
mounted inside the switchgear cubicle supported by moulded epoxy, fibre
glass or porcelain insulators. For higher current rating copper bus bars are
sometimes used in switchgears.
LV Switchgears:
LV switchgears feed power supply to motors above 110 KW and upto160 KW
rating and to Motor Control Centres (M.C.C). LV system is also a grounded
system where the neutral of transformers are solidly connected to ground. The
duty involves momentary loading, total load throw off, direct on line starting
of motors and under certain emergency condition automatic transfer of loads
from one source of supply to the other. The switchgear consists of metal clad
continuous line up of multitier draw out type cubicles of simple and robust
construction. Each feeder is provided with an individual front access door. The
main bus bars and connections shall be of high grade aluminium or aluminium
alloy sized for the specified current rating. The circuit breakers used in the
LV switchgear shall be air break 3 pole with stored energy, trip free shunt trip
mechanism. These are draw out type with three distinct position namely, Service,

Test and Isolated. Each position shall have mechanical as well as electrical
indication. Provision shall be there for local and remote electrical operation of the
breakers. Mechanical trip push button shall be provided to trip manually in the
event of failure of electrical trip circuit. Safety interlocks shall be provided to
prevent insertion and removal of closed breaker from Service position to Test
position and vice versa..
Two Main Bus and One transfer Bus scheme:
In this scheme there is an arrangement for a duplicate main bus (MB). All the
feeders in the yard may be connected to either MB # 1 or MB # 2 or
may be divided in two groups and distributed in two buses. In case of outage
of any circuit breaker that feeder can be diverted through bus coupler breaker.
Bus tie breaker is used to tie up MB #1 & MB # 2.
GENERATOR PROTECTION
The purpose of generator protection is to provide protection against abnormal
operating condition and during fault condition. In the first case the machine and
the associated circuit may be in order but the operating parameters (load,
frequency, temperature) and beyond the specified limits. Such abnormal
running condition would result in gradual deterioration and ultimately lead
to failure of the generator.
Protection under abnormal running conditions
a) Over current protection: The over current protection is used in generator
protection against external faults as back up protection. Normally external short
circuits are cleared by protection of the faulty section and are not dangerous to
the generator. If this protection fails the short circuit current contributed
by the generator is normally higher than the rated current of the generator and
cause over heating of the stator, hence generators are provided with back
up over current protection which is usually definite time lag over current relay.
b) Over load protection: Persistent over load in rotor and stator circuit
cause heating of winding and temperature rise of the machine. Permissible
duration of the stator and rotor overload depends upon the class of insulation,
thermal time constant, cooling of the machine and is usually recommended
by the manufacturer. Beyond these limits the running of the machine is
not recommended and overload protection thermal relays fed by current
transformer or thermal sensors are provided.

c) Over voltage protection: The over voltage at the generator terminals
may because by sudden drop of load and AVR malfunctioning. High voltage
surges in the system (switching surges or lightning) may also cause over
voltage at the generator terminals. Modern high speed voltage regulators adjust
the excitation current to take care against the high voltage due to load
rejection. Lightning arresters connected across the generator transformer
terminals take care of the sudden high voltages due to external surges. As such
no special protection against generator high voltage may be needed. Further
protection provided against high magnetic flux takes care of dangerous increase
of voltage.
d) Unbalance loading protection: Unbalance loading is caused by single
phase short circuit outside the generator, opening of one of the contacts of the
generator circuit breaker, snapping of conductors in the switchyard or excessive
single phase load. Unbalance load produces –ve phase sequence current
which cause overheating of the rotor surface and mechanical vibration.
Normally 10% of unbalance is permitted provided phase currents do not
exceed the rated values. For –ve phase sequence currents above 5-10% of
rated value dangerous over heating of rotor is caused and protection against this
is an essential requirement.
e) Loss of prime mover protection: In the event of loss of prime mover
the generator operates as a motor and drives the prime mover itself. In some cases
this condition could be very harmful as in the case of steam turbine sets
where steam acts as coolant, maintaining the turbine blades at a constant
temperature and the failure of steam results in overheating due to friction and
windage loss with subsequent distortion of the turbine blade. This can be sensed
by a power relay with a directional characteristic and the machine can be taken
out of bar under this condition. Because of the same reason a continuous very low
level of output from thermal sets are not permissible.
Protection under fault condition
a) Differential protection: The protection is used for detection of internal
faults in a specified zone defined by the CTs supplying the differential relay.
For an unit connected system separate differential relays are provided for
generator, generator transformer and unit auxiliary transformer in addition to
the overall differential protection. In order to restrict damage very high
differential relay sensitivity is demanded but sensitivity is limited by C.T
errors, high inrush current during external fault and transformer tap changer
variations.

b) Back up impedance protection: This protection is basically designed as back
up protection for the part of the installation situated between the generator
and the associated generator and unit auxiliary transformers. A back up
protection in the form of minimum impedance measurement is used, in which the
current windings are connected to the CTs in the neutral connection of the
generator and its voltage windings through a P.T to the phase to phase
terminal voltage. The pickup impedance is set to such a value that it is only
energized by short circuits in the zone specified above and does not respond to
faults beyond the transformers.
c) Stator earth fault protection: The earth fault protection is the protection of
the generator against damages caused by the failure of insulation to earth.
Present practice of grounding the generator neutral is so designed that the
earth fault current is limited within 5 and 10 Amp. Fault current beyond this limit
may cause serious damage to the core laminations. This leads to very high eddy
current loss with resultant heating and melting of the core.
d) 95% stator earth fault protection: Inverse time voltage relay connected
across the secondary of the high impedance neutral grounding transformer relay
is used for protection of around 95% of the stator winding against earth fault.
e) 100% stator earth fault protection: Earth fault in the entire stator circuits
are detected by a selective earth fault protection covering 100% of the
stator windings. This 100% E/f relay monitors the whole stator winding by means
of a coded signal current continuously injected in the generator winding
through a coupling. Under normal running condition the signal current flows
only in the stray capacitances of the directly connected system circuit. .
f) Rotor earth fault protection: Normally a single rotor earth fault is
not so dangerous as the rotor circuit is unearthed and current at fault point is zero.
So only alarm is provided on occurrence of 1st rotor earth fault. On occurrence
of the 2nd rotor earth fault between the points of fault the field winding
gets short circuited. The current in field circuit increases, resulting in heating
of the field circuit and the exciter. But the more dangerous is disturbed
symmetry of magnetic circuit due to partial short circuited coils leading to
mechanical unbalance.
Industrial Batteries

Features of the Batteries:
 Unmatched high discharge performance.
 Long and reliable service life – lives in excess of 20 years obtained when
operated on float or trickle charge.
 100 % capacity retained throughout life span.
 Low maintenance – minimal topping up frequency and self-discharge.
 Superior all round voltage profile and energy (Wh) output.
 Capability of rapid recharging.
 Boost charge not essential.
 Transparent containers for ease of inspection and maintenance.
Applications of the Batteries: EXIDE / CHLORIDE high performance
PLANTE range of cells are suitable for standby duties in Telephone Exchanges,
Power House, UPS system.
Recharge Instructions: All PLANTE cells should normally be floated at a mean
float voltage of 2.23 ±0.02 V per cell. Should there be any limitation in the
charger capacity or load, PLANTE cells may also be floated at a lower float
voltage of 2.18 to 2.2 V per cell. Trickle charging currents should be so adjusted,
anywhere between the maximum and minimum allowed levels given in the table,
such the individual cells remain fully charged
220 V DC system:
For the 3x210 MW units there are 3 numbers of DC distribution boards in the
inside powerhouse like DCDB#1, DCDB#2 and DCDB#3 (one for each unit).
In the outside powerhouse of 3x210 Mw units there are four number of DC
distribution boards which is in CWPH, 220 KV switchyard, RIPH and BIPH. In
normal operating condition battery shall be in float charging mode.
24 V DC system
24 V DC power is used in control & instrumentation system and
annunciation circuit at BTG control room. For the three units, there are three

numbers of DC distribution boards i.e. one for each unit. Normally 24 V DCDBs
are fed from their respective battery & battery charger. 24 V DCDB has a two
number of bus section along with bus coupler.
220 V Battery charger scheme
 Technical specification
Float Charger (Main / Standby)
Input power supply
Output voltage Auto 236.5 V
Manual 220 – 253 V
Output Current 300 A DC continuous plus trickle charging current of 1440 mA
max.
Output
regulation load variation.
Output Ripple Around 1% at full load of 236.5 V
Control
configuration
3-phase full wave full control thyristorised bridge fed through
3-phase
Transformer and controlled by AVR.
 Total unit consists of 2 numbers identical automatic / manual float charger
and 1 number manual boost charger.

 Float Charger (main / standby):
The float charger is meant for supplying the continuous DC load and at the
same time float charging the battery to keep it in fully charged condition. The
float charger may either be operated in auto or manual mode. In the automatic
mode, the output voltage is held constant at a preset value (2.15 v/cell) whereas
in manual position the output voltage may vary within limits by an external
potentiometer. The incoming supply to the float charger is fed to a double
wound step down transformer through suitably rated switch and fuses, the
secondary of which is further fed to a 3-phase full wave full control
thyristorised bridge through line surge suppressor and high speed
semiconductor fuses. The bridge circuit is consisted of 6 numbers thyristors
protected by snubber circuit against voltage surge. The triggering of the
thyristors is controlled by the AVR unit, which senses feedback from the
output voltage and current. These feedback signals are suitably processed and
compared with the reference generated in the AVR circuits. Then the error is
amplified and phase compensated by high gain operational amplifier. The
incorporation of feedback ensures automatic correction of any deviation of the

set voltage, which may arise due to line or load fluctuation. The output of the
final amplifier is fed to the triggering circuits, which controls the output
voltage of the float charger by adjusting the firing angle of the thyristors. With
the help of the AVR unit the regulation of the output voltage of the float
charger may be kept around.
1% against line or load fluctuations. The AVR unit also renders the unique
current limiting features due to incorporation of inner current loops, by which
the output voltage drops as the rated load is increased thereby automatically
transferring the load to the battery in order to avoid the overloading of the
charger. The solid state over current relay on DC side and thermal overload
relay on AC side are provided for further protection. Over current relay and
thermal over load relay are so interlocked that in case of fault monitored by
them the AC contactor of respective charger will be automatically shut off.
Both the main and standby float chargers are of identical rating so
that in case of failure of one the other can take care of the total load.
 Boost charger:
Boost charger is basically meant for quick charging the battery after a heavy
discharge so as to restore the capacity of the battery within minimum time. The
3-phase AC supply voltage is fed to a suitable rated step down transformer
through switch fuse unit, the secondary voltage of the transformer is fed through
line surge suppressor and high speed semiconductor fuses to a 3-phase full wave
full controlled thyristorised bridge which are adequately protected by snubber
network as protection against voltage surge. The bridge circuit is consists of 6
numbers thyristors. The firing of the Thyristor Bridge is controlled manually by
adjusting the potentiometer provided on the front door of the panel to monitoring
the charging current. In this system the battery will normally float across the
float charger so that in case of power failure the battery can maintain the load
without interruption. However, after heavy drainage the battery should be placed
on the boost charger manually so as to charge the battery at recommended
starting rate. If the supply now fails, the battery will immediately be connected
to the load bus by the N/O contact of the DC contactor (DC1), which is
interlocked, with auxiliary contact of the boost charger AC contactor C3 (drops
out when AC supply fails). The DC contactor (DC1), which remains de-
energized when supply is present and the battery is in boost charging condition
to disconnect the battery and battery charger, form the load bus, to maintain the
output varies within the wide limits depending on the battery voltage. If power
supply fails while boost charging is in progress the battery will be connected to
the load automatically to avoid any interruption. A diode bank is incorporated
between the intermediate cell and the load bus. During normal operation the
diode will be reverse biased. In the event of power failure during boost charging
with battery isolated, the output voltage will start dropping. As soon as it drops

slightly lower than the intermediate cell voltage, the diode bank will start
conduct thereby maintaining the voltage at the load bus, through lower in
magnitude, to avoid any interruption of load supply. However, after this interval,
the DC contactor will energize thereby connecting the battery to the load bus
and restricting the original load voltage.
 The automatic voltage regulator (AVR) circuit is the heart of the system,
which maintains stable output DC voltage of the charger in spite of supply
voltage fluctuations and load variations.
ELECTRICAL TESTING
1.IR (INSULATION RESISTANCE) TESTING of underground cables,
motors and alternators
2.HIGH POTENTIAL TEST (HIPOT TEST) for motors, alternators, cables
and bus duct
3.WINDING RESISTANCE TEST for alternators, motors and transformers
4.AC IMPEDANCE TEST of stator of motor
5.REPETATIVE SURGE OSCILLOGRAPH (RSO)TEST of rotor of motor
6.TAN DELTA TEST of transformer bushing
7.TIMING MEASUREMENT OF CIRCUIT BREAKER
8.CONTACT RESISTANCE TEST OF CIRCUIT BREAKER
9.VACUUM TEST OF VCB
10.OIL TEST OF TRANSFORMER
11.FORM TEST OF TRANSFORMER
12.SWITCH FREQUENCY RESPONSE ANALYSIS
Reduced voltage test of SF6 breaker Relay testing by power system simulator
Transformer oil test kit Online Moisture in oil test kit

CONCLUSION
MTPS is the largest among the thermal power plants established pan India by
DVC, with a rated generation capability of 2340 MWh combining all 8 units.
Vocational Training opportunities provided by DVC to Electrical engineering
undergraduates has proven itself to be instrumental for better understanding of
electrical operations in a thermal power plant. Applications of Generator &
Transformer and Switchyard-protection are one of the crucial components of
electrical power generation and distribution, all of which were physically
perceived during the span of three weeks of the VT. The vitality of Electrical
Testing of all electricity operated components for safety and planned
maintenance in a power plant was realized practically.
I would like to thank everybody who has been a part of this project, without
whom this project would never have been completed with such ease.
BIBLIOGRAPHY
1) Mejia Thermal Power Station Electrical Operation Manual by Rajib
Saha
2) Electrical Testing Manual
3) Practical Boiler Operation by Amiya Ranjan Mullick
4) Thermal Power Engineering by R.K.Rajput
5) Switchgear and Protection by S.S.Rao

Mtps project report

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