Training on MTPS, DVC...

1. Project Report
ON MEJIA THERMAL POWER PLANT
Suvajit Khan | Electrical Engineering | January 8, 2014
Brainware Group of Institutions, Barasat, Kolkata

2. Preface
This Project Report has been prepared in fulfilment of Industrial Training to be
carried out in 3rd year of our B.TECH course. For preparing the Project Report, we
have visited Mejia Thermal Power Station under Damodar Valley Corporation
during the suggested duration for the period of 21 days, to avail the necessary
information. The blend of learning and knowledge acquired during our practical
studies at the company is presented in this Project Report.
The rationale behind visiting the power plant and preparing the Project Report is
to study the mechanical overview, electrical overview, various cycles’ and processes
(viz. Steam Generation, Turbo Generation and Balance of Plant) of power
generation and details of control and instrumentation required in thermal power
plant.
We have carried out this training under well experienced and highly qualified
engineers of MTPS, DVC of various departments’ viz. Mechanical, Electrical,
Chemical and Control & Instrumentation depts. We have taken the opportunity to
explore the Electrical Department, its uses, necessity in power plant and
maintenance of various instruments used for monitoring and controlling the
numerous processes of power generation. We have tried our level best to cover all
the aspects of the power plant and their brief detailing in this project report.
The main aim to carry out this training is to familiarize ourselves with the real
industrial scenario, so that we can relate with our engineering studies.
PAGE 1

3. Acknowledgement
Itake this opportunity to express my profound gratitude and deep regards to my
guide Mr. P. K. Dubey for his exemplary guidance, monitoring and constant
encouragement throughout the course of this thesis. The blessing, help and
guidance given by him time to time shall carry me a long way in the journey of life
on which I am about to embark.
I also take this opportunity to express a deep sense of gratitude to Mr. Bidhayak
Dutta, The Dy. Chief Engineer (ELEC.), DVC MTPS, for his cordial support,
valuable information and guidance, which helped me in completing this task
through various stages.
I am obliged to staff members of (DVC MTPS), for the valuable information
provided by them in their respective fields. I am grateful for their cooperation
during the period of my assignment.
Lastly, I thank almighty my teammate for his constant encouragement without
which this assignment would not be possible.
PAGE 2

4. <<Contents>>
Page No.
1.
2.
3.
4.
Introduction ..............................................................................................4
Technical Specification of Mejia thermal power plant……………….....5
Overview of a Thermal power plant......................................................6
Mechanical operation
a. Coal handling Plant................................................................................7
b. Water Treatment Plant..........................................................................8
c. Water De-mineralization Plant.............................................................9
d. Boiler System..........................................................................................10
e. Ash handling plant.................................................................................15
f. ESP...........................................................................................................15
g. Boiler auxiliaries……………………………………………………………………………...16
h. Steam Turbine........................................................................................18
i. Cooling tower.........................................................................................20
j. Chimneys………………………………………………………………………………………...20
5. Electrical operation
a. Generator………………………………………………………………………………………….21
b. Transformers…………………………………………………………………………………….25
c. AC & DC Power Flow in Thermal Power Station……………………………...30
d. Switchyard Section…………………………………………………………………………...31
e. Switchgear………………………………………………………………………………………...36
f. Protection………………………………………………………………………………………….37
g. Battery Bank……………………………………………………………………………………...39
h. DVC: Transmission & Distribution Network…………………………………….41
6. Conclusion………………………………………………………………………………………..43
7. Bibliography…………………………………………………………………………………..…44
PAGE 3

5. Introduction
Damodar Valley Corporation was established on 7th July 1948.It is the most
reputed company in the eastern zone of India. DVC is established on the Damodar
River. It also consists of the Durgapur Thermal Power Plant in Durgapur. The
MTPS under the DVC is the second 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 DamodarValley Corporation
in the state of West Bengal. The total power plant campus area is surrounded by
boundary walls and is basically divided into two major parts, first the Power Plant
area itself and the second is the Colony area for the residence and other facilities
for MTPSs employees.
PAGE 4

6. Technical Specification of MTPS:
INSTALLED CAPACITY:  Total number of Units: - 4 X 210 MW (unit 1 to 4) with Brush Type
Generators, 2 X 250 MW (unit 5 and 6) with Brush less Type Generators,
and 2*500 MW (unit 7 and 8) Brushless Type Generators.
 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
Station
Unit No.
Capacity
(MW)
Boiler Maker
Turbine
Maker
Mejia TPS
1,2,3,4,
5&6
210
250
BHEL
BHEL
BHEL
BHEL
Mejia TPS
Phase:-II
7&8
500
BHEL
BHEL
In a Thermal Power generating unit, combustion of fossil fuel (coal, oil or natural
gas) in Boiler or fissile element (uranium, plutonium) in Nuclear Reactor generates
heat energy. This heat energy transforms water into steam at high pressure and
temperature. This steam is utilized to generate mechanical energy in a Turbine.
This mechanical energy, in turn is converted into electrical energy with thehelp of
an Alternator coupled with the Turbine. The production of electric energy utilizing
heat energy is known as thermal power generation. The heat energy changes into
mechanical energy following the principle of Rankine reheat-regenerative cycle
and this mechanical energy transforms into electrical energy based on Faraday’s
laws of electromagnetic induction. The generated output of Alternator is electrical
power of three-phase alternating current (A.C.). A.C. supply has several advantages
over direct current (D.C.) system and hence, it is preferred in modern days. The
voltage generated is of low magnitude (15.75 KV) and is stepped up suitably with
the help of transformer for efficient andeconomical transmission of electric power
from generating stations to different load centers at distant locations.
PAGE 5

7. 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, i.e.
chemical energy to electrical energy conversion takes place. The working fluid is
water which is sometimes in liquid phase and sometimes in vapourphase 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 utilized by the electric generator to produce
electricity and ultimately transmitted via the transmission lines.
PAGE 6

8. MECHANICAL OPERATION
Coal Handling Plant (CHP):
Generally most of the thermal power plants uses low grades bituminous coal. The conveyer belt
system transports the coal from the coal storage area to the coal mill. Now the FHP (Fuel Handling
Plant) department is responsible for converting the coal converting it into fine granular dust by
grinding process. The coal from the coal bunkers. Coal is the principal energy source because of its
large deposits and availability. Coal can be recovered from different mining techniques like:
Shallow seams by removing the over burnt expose the coal seam.
Underground mining.
The coal handling plant is used to store, transport and distribute coal which comesfrom the mine.
The coal is delivered either through a conveyor belt system or by rail or road transport. The bulk
storage of coal at the power station is important for the continuous supply of fuel. Usually the
stockpiles are divided into three main. Categories:
Live storage
Emergency storage
Long term compacted stockpile.
The figure below shows the schematic representation of the coal handling plant. Firstly the coal
gets deposited into the track hopper from the wagon and then via the paddle feeder it goes to the
conveyer belt#1A. Secondly via the transfer port the coal goes to another conveyer belt#2B and then
to the crusher house. The coal after being crushed goes to the stacker via the conveyer belt#3 for
being stacked or reclaimed and finally to the desired unit. ILMS is the inline magnetic separator
where all the magnetic particles associated with coal get separated.
COAL HANDLING PLANT PROCEDURE
PAGE 7

9. Water Treatment Plant:
Raw water supply:
Raw water received at the thermal power plant is
passed through Water Treatment Plant to separate
suspended impurities and dissolved gases including
organic substance and then through De-mineralized
Plant to separate soluble impurities.
Deaeration:
In this process, 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 of 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
to ferric ions. These ferric ions promote to some extent in coagulation process.
Coagulation:
Coagulation takes place in clariflocculator. Coagulant destabilizes 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. Filter beds are developed by placing gravel or coarse
anthracite and sand in layers. These filter beds are regenerated by backwashing and air blowing
through it.
Chlorination:
Neutral organic matter is very heterogeneous i.e. it contains many classes of highmolecular
weight organic compounds. Humic substances constitute a major portion ofthe dissolved
organic carbon from surface waters. They are complex mixtures of organiccompounds with
relatively unknown structures and chemical composition.
PAGE 8

10. De-Mineralized Water plant (DM Plant):
A DM plant generally consists of cation, anion, and mixed bed exchangers. Any
ions in the final water from this process consists essentially of hydrogen ions
hydroxide ions, which recombine to form pure water. Very pure DM water
becomes highly corrosive once it absorbs oxygen from the atmosphere because of
its very high affinity for oxygen.
The capacity of the DM plant is dictated by the type and quantity of salts in the
raw water input. However, some storage is essential as the DM plant may be down
for maintenance. For this purpose, a storage tank is installed from which DM
water is continuously withdrawn for boiler make-up. The storage tank for DM
water is made from materials not affected by corrosive water, such as PVC. The
piping and valves are generally of stainless steel. Sometimes, a steam blanketing
arrangement or stainless steel doughnut float is provided on top of the water in
the tank to avoid contact with air. DM water make-up generally added at the
steam space of the surface condenser (i.e., the vacuum side). This arrangement not
only sprays the water but also DM water gets de-aerated, with the dissolved gases
being removed by a de-aerator through an ejector attached to the condenser.
PAGE 9

11. 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 subcritical 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).
PAGE 10

12. 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
PAGE 11

13. 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 super heaters 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.
ii.
iii.
iv.
Boiler bottom ring header drains
Boiler drum drains & vents
Superheater&Reheater headers drains & vents
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.
PAGE 12

14. 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
3
Volume
5240 m
Fuel heat input per hour
106 kcal
Designed pressure
175.8 kg/cm
Superheater outlet pressure
155 kg/cm
2
2
2
Low temperature SH (horizontally spaced)
2849 m (total heating surface area)
Platen SH (Pendant platen)
1097 m (total heating surface area)
Final superheater (vertically spaced)
1543 m (total heating surface area)
2
2
ATTEMPERATOR:
Type
Spray
No. of Stages
One
Spray Medium
Feed water from boiler feed pump (BFP)
REHEATER:
Type
Total H.S. area
Control
Vertical Speed
2819 m
2
Burner tilt & excess air
ECONOMIZER:
Type
Total H.S. area
Plain Tube
6152 m
2
PAGE 13

15. PAGE 14

16. 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:




Quenching reduces the temperature of ash.
It reduces the corrosive action of ash.
Ash forms clinkers by fusing in large lumps and by quenching clinkers will disintegrate.
Quenching reduces the dust accompanying the ash.
Flyash is collected with an electrostatic precipitator(ESP).
Electrostatic Precipitator(E.S.P):
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 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.
PAGE 15

17. TECHNICAL DATA OF THE ESP:
3
Gas flow rate
339 m /s
Temperature
142°C
Dust Concentration
62.95 gm./N-cubic meter
COLLECTING ELECTRODES:
No. of rows of collecting electrode per field
49
No. of collecting electrode plate
294
Total no. of collecting plates per boiler
3528
Nominal height of collecting plate
13.5 m
Nominal length of collecting electrodes per
field in the direction of gas field
4.5 m
Nominal width of collecting plate
750 mm
2
Specific collecting area
206.4 m /cubic meter. sec
-1
ELECTRICAL ITEMS:
Rectifier
Silicon diode full wave bridge connection
Located
Mounted on the top of the precipitator
Type of control
SCR (Silicon Controlled Rectifier)
Number
24
Location
In the control room at ground level
Number
2
Equipment Controlled
Geared motors of rapping mechanism of
collecting & emitting electrodes
Location
Motors
24
Type
Auxiliary Control
Panel
70 kV (peak), 80 mA (mean)
Number
Rectifier Control Panel
Rating
In the control room at the ground level
Quantity
24
Rating
Geared motor 0.33 HP, 3 phase, 415 V, 50
Hz
Location
On root panels of the casing
PAGE 16

18. BOILER AUXILARIES
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 AT UNIT # 1:
No. of boiler
3
Type
Radial, NDZV 31 Sidor
Medium handled
Flue Gas
Location
Orientation
Ground Floor
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 AT UNIT # 1:
No. of boiler
2
Type
Radial, NDZV 28/Sidor
Medium handled
Clean air
Location
Orientation
Ground floor
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.
PAGE 17

19. TECHNICAL DATA OF THE P.A.FAN AT UNIT# 1:
No. of boiler
Type
3
Radial, NDZV 20 Heracles
Medium handled
Location
Orientation
Hot air
Ground Floor
Suction—Vertical/45 degrees to Horizontal
Delivery—Bottom Horizontal.
Coal mill or pulveriser:
Most efficient way of utilizing coal for steam generation is to burn it in pulverized form. The coal is
pulverized in coal mill or pulveriser to fineness such that 70-80% passes through a 200 mesh sieve.
The factors that affect the operation of the mill or reduce the mill output are:
o
o
o
o
o
Grind ability of coal: Harder coal (i.e. coal having lower hard-grove index (H.G.I.)) reduces
mill output and vice versa.
Moisture content of coal: More the moisture content in coal, lesser will be the mill output
& vice versa.
Fineness of output: Higher fineness of coal output reduces mill capacity.
Size of coal input: Larger size of raw coal fed to the mill reduces mill output.
Wear of grinding elements: More wear and tear of grinding elements reduces the output
from mill.
Fuel oil system:
In a coal fired boiler, oil firing is adopted for the purpose of warming up of the boiler or assisting
initial ignition of coal during introduction of coal mill or imparting stability to the coal flame
during low boiler load condition. Efficient or complete combustion of the fuel oil is best achieved
by atomizing oil by compressed air for light oil (LDO) or by steam for heavy oil (HFO) in order to
have proper turbulent mixing of oil with combustion air. Use of HFO is beneficial with respect to
LDO in view of its lower cost and saving in foreign exchange.
The oil burners and igniters are the basic elements of oil system. Oil is supplied by light oil pump
or by heavy oil pump through oil heater. Steam heater reduces the viscosity of heavy oil and aids
flow ability as well as better atomization. The oil burners are located in the compartmented corner
of wind boxes, in the different elevation of auxiliary air compartments, sandwiched between the
coal burner nozzles. Each oil burner is associated with an igniter, arranged at the side.
PAGE 18

20. Steam Turbine:
A steam turbine is a prime mover which continuously converts the energy of high pressure, high
temperature steam supplied by the boiler into shaft work with low pressure, low temperature steam
exhausted to a condenser.
210 MW (KWU) steam turbine (Mejia TPS U # 1, 2, 3 & 4):
2
o
HP turbine inlet seam: 147 kg/cm and 537 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.
2
o
Reheated steam pressure and temperature: 34.5 kg/cm and 537 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 LPTdouble flow with 8 stages per flow. Six steam extractions for feed/condensate water heating have
th
been taken from HPT exhaust & 11 stages of IPT for high pressure heaters, from IPT exhaust for
rd
th
th
de-aerator and from 3 , 5 & 7 stages of LPT for low pressure heaters. The individual turbine
rotors and the generator rotor are connected by rigid couplings.
PAGE 19

21. 250 MW (KWU) steam turbine (Mejia TPS U # 5 & 6):
2
0
HP turbine inlet steam: 147.10 kg/cm and 537 C. Steam entry to HP turbine through two combined
2
0
main stop & control valves. Reheated steam pressure and temperature: 34.95 kg/cm and 537 C. 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
th
taken from HPT exhaust & 11 stages of IPT for high pressure heaters, form IPT exhaust for derd
th
th
aerator and from 3 , 5 & 6 stages of LPT for low pressure heaters. The individual turbine rotors
and the generator are connected by rigid couplings.
500 MW(KWU) Steam turbine (Mejia TPS U #7&8):
2
0
HP turbine inlet steam: 170 kg/cm and 535 C. Steam entry to HP turbine through two combined
stop and control valves and to IP turbine through four combined reheat stop and control valves.
2
0
Reheated steam pressure and temperature: 34 kg/cm and 535 C. 500 MW KWU turbine is a
tandem compounded, three cylinders, single reheat condensing turbine provided entirely with
reaction blading.
Maker
Type
Type of governing
Number of cylinders
Speed(RPM)
Rated output(KW)
BHEL
Reaction turbine
Throttling
3
3000
210000(for unit1,2,3,4)
250000(for unit 5 & 6)
Steam pressure before emergency stop valve
150 kg/cm
2
(abs)
Steam temperature before emergency stop
valve
Reheat temperature
535°C (for unit1,2,3,4)
537°C (for unit 5 & 6)
535°C (for unit 1,2,3 &4)
537°C (for unit 5 & 6)
PAGE 20

22. Cooling Tower
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. Wet cooling
towers could be mechanically draught or natural draught. In M.T.P.S the cooling towers are I.D.
type for units 1-6 and natural draught for units 7&8.
Chimneys
A chimney may be considered as a cylindrical hollow tower made of bricks or steel. In MTPS the
chimneys of eight units are made of bricks. Chimneys are used to release the exhaust gases (coming
from the furnace of the boiler) high up in the atmosphere. So, the height of the chimneys are made
high.
PAGE 21

23. ELECTRICAL OPERATION
The electrical operation of a power plant comprises of generation, transmission and distribution of
electrical energy. In a power station both distribution and transmission operation can take place.
When power is sent from power station to all other power station in the grid, it is known as
distribution of power. When power plant is driving power from other power station it is known as
transmission of power/electrical energy.
Electrical Generator:
In M.T.P.S. there are 6 electric generators for units 1 to 6. These are 3 phase turbo generators, 2 pole
cylindrical rotor type synchronous machines which are directly coupled to the steam turbine. The
generator consist of 2 parts mainly the stator and the rotor.
The transformation of mechanical energy into electrical energy is carried out by generator. The
A.C. generator or alternator is based on the principal of electromagnetic induction and generally
consists of a stationary part called stator and a rotating part called rotor. The stator houses the
armature windings and the rotor houses the field windings. A D.C. voltage is applied to the field
winding in the rotor through slip rings, when the rotor is rotated, the lines of magnetic flux is cut
through the stator windings. This as a result produces an induced e.m.f. (electromotive force) in
the stator winding which is tapped out as output. The magnitude of this output is determined by
the equation:
E= 4.44*Ø*f* N volts
Where, E=e.m.f. induced;
Ø=Strength of magnetic field in Weber;
F=Frequency in cycles per second or in hertz;
N=Number of turns in the winding of the stator;
Again, f=P*n/120
Where, P=Number of poles;
n=Revolutions per second of the rotor.
Form the above expression it is clear that for the same frequency number of poles increases with
decrease in speed and vice versa. Therefore low speed hydro turbine drives generators have 14 to 20
poles whereas for high speed steam turbine driven generators have 2 poles.
PAGE 22

24. Generator Components:
Rotor:Rotor is the most difficult part to construct; it revolves at a speed of 3000 rpm. The massive
non-uniform shaft subjected to a multiplicity of differential stresses must operate in oil lubricated
sleeve bearings supported by a structure mounted on foundations all of which poses complex
dynamic behavior peculiar to them. It is also an electromagnet and to give it the necessary
magnetic strength the windings must carry a fairly high current. The rotor is a cast steel ingot and
it is further forged and machined. Very often a hole bored through the center of the rotor axially
from one end to the other for inspection. Slots are then machined for windings and ventilation.
Rotor Windings:
Silver bearing copper is used for the winding with mica as insulation
between conductors. A mechanically strong insulator such as micanite is used for lining the slots.
For cooling purpose slots and holes are provided for circulation of cooling gas. The wedges the
windings when the centrifugal force developed due to high speed rotation tries to lift the windings.
The two ends of the winding are connected to slip rings made of forged steel and mounted on
insulated sleeves.
PAGE 23

25. Stator:The major part of the stator frame is the stator core, it comprises of inner and outer frame.
The stator core is built up of a large number of punching or section of thin steel plates. The use of
cold rolled grain-oriented steel can contribute to reduction of stator core.
Stator Windings:each stator conductor must be capable of carrying the rated current without
overheating. The insulation must be sufficient to prevent leakage current flowing between the
phase to earth. Windings for the stator are made up from copper strips wound with insulated tape
switch is impregnated with varnish, dried under vaccum and hot pressed to form a solid insulation
bar. In 210MW generators the windings are made up of copper tubes through which water is
circulated for cooling purpose.
Generator Cooling and Sealing System:
1)
Hydrogen Cooling System: Hydrogen is used as cooling medium in large capacity
generators in view of its high heat carrying capacity and low density. But in view of its
explosive mixture with oxygen, proper arrangement for filling, purging and maintaining its
purity inside the generator have to be made. Also in order to prevent escape of hydrogen
from the generator casing, shaft sealing system is used to provide oil sealing. The system is
capable of performing the following functions:
a) Filling in and purging of hydrogen safely.
b) Maintaining the gas pressure inside the machine at the desired value all the time.
c) Provide indication of pressure, temperature and purity of hydrogen.
d) Indication of liquid level inside the generator.
PAGE 24

26. 2) Generator Sealing System:Seals are employed to prevent leakage of hydrogen from
the stator at the point of rotor exit. A continuous film between the rotor collar and the seal
liner is maintained by means of oil at the pressure which is about above the casing
hydrogen gas pressure. The thrust pad is held against the collar of rotor by means of thrust
oil pressure, which is regulated in relation to the hydrogen pressure and provides the
positive maintenance of the oil film thickness. The shaft sealing system contains the
following components:
a) A.C. oil pump
b) D.C. oil pump
c) Oil injector
d) Differential Pressure Regulator
e) Damper tank
Excitation Systems:
1) Static Excitation:
Alternator terminal voltage is used here.
SCR-based controlled rectifier is supplied from alternator output through step
down transformer.
SCR gate signal are derived from alternator output through CT & PT.
Rectifier output voltage is fed to the alternator field winding.
To generate the alternator output, it is run at rated speed with its field supplied
from a separate D.C. supply bank.
This scheme is less expensive & requires little maintenance.
Excitation energy depends on alternator speed.
2) Brushless Excitation:
Main shaft of prime movers drives pilot exciter, main exciter & the main
alternator.
Pilot exciter is a permanent magnet alternator.
Pilot exciter feeds 3-phase power to main exciter.
Main exciter supplies A.C. power to silicon diode bridge rectifier through hollow
shaft which feeds the D.C. to the field of main alternator.
SCR gate signals are derived from alternator output through CT & PT.
This scheme is mainly employed in turbo alternators.
PAGE 25

27. PARAMETERS
UNIT-1
UNIT-2
UNIT-3
UNIT-4
UNIT-5
UNIT-6
Maker
BHEL
BHEL
BHEL
BHEL
BHEL
BHEL
Kw
210000
210000
210000
210000
250000
250000
P.F.
0.85 lag
0.85 lag
0.85 lag
0.85 lag
0.85 lag
0.85 lag
KVA
247000
247000
247000
247000
294100
294100
Stator
Volts15750
Amps9050
Volts15750
Amps9050
Volts15750
Amps9050
Volts15750
Amps9050
Volts15750
Amps10781
Volts16500
Amps10291
Rotor
Volts- 310
Amps2600
Volts- 310
Amps2600
Volts- 310
Amps2600
Volts- 310
Amps2600
Volts- 292
Amps2395
Volts- 292
Amps2395
R.P.M.
3000
3000
3000
3000
3000
3000
Hz
50
50
50
50
50
50
Phase
3
3
3
3
3
3
Connection
YY
YY
YY
YY
YY
YY
Coolant
Hydrogen
& Water
Hydrogen
& Water
Hydrogen
& Water
Hydrogen
Hydrogen
Hydrogen
Gas Pressure
3.5 BAR(G)
3.5 BAR(G)
3.5 BAR(G)
2 BAR(G)
3 BAR(G)
3 BAR(G)
Insulation
Class
B
B
B
F
F
F
Year of
Establishment
1996
1998
1999
2005
2008
2009
Specification of Generators:
Transformers:
It is a static device which transfers electric powers from one circuit to the other without
any change in frequency, but with a change in voltage and corresponding current levels
also.
Here the transformers used are to transfer electric power from 15.75 KV to 220KV or 400KV
that are provided to the national grid.
The step-up generator transformers are of ONAN/ANOF/AFOF cooling type.
PAGE 26

28. Neutral Grounding Transformer (NGT):
The NGT is used to prevent the generator from earth faults.
It comprises of primary winding and secondary winding, the secondary winding is
connected with a high value resistance. Whenever earth fault arises heavy current flows to
the primary winding and as a result an e.m.f is induced in the secondary.
The voltage drop across the resistance is sensed by the NGT relay and it actuate the
Generator Circuit Breaker (GCB) and thus the generator is tripped.
Limited Earth-Fault Earthling System: Generators and other apparatus installed at higher
voltage levels are exposed to much greater fault energy in the order of thousands of MVA.
Earth-fault currents could damage iron structures in generators, motors, and transformers,
so that they can’t be repaired, but instead must be replaced…. At great cost! Hence, some
method of current limiting, like NGT (Neutral Grounding Transformer) or NGR (Neutral
Grounding Resistor) is beneficial.
Power Transformer:
Power Transformers enhances the productivity as well as maximizes the capacity level of
the high power supply equipment.
These are ultimate for the regular power without any cut off. They are used for control high
voltage and frequency for the different systems.
Power Transformers have the following standards:
 They can assist three phases.
 There ratings are up to 2000 KVA.
 Copper and Aluminium winding material is used in this
 Applicable Standards are IS, IEC, ANSI, JIS, etc.
 It is sufficient for primary as well as secondary voltage.
Auto Transformer:
High voltage auto-transformers represent an important component of bulk transmission
systems and are used to transform voltage from one level to another.
These auto-transformers are critical for regional load supply, inter-regional load transfers
and for certain generator/load connections.
Major or catastrophic failures to this equipment can have severe consequences to electric
utilities in terms of increased operating costs and customer load losses.
To minimize the impact of this type of failures, utilities may carry some spare units to
guard against such events. These spare units are going to cost utilities money (utility cost)
to purchase, to store and to maintain and utilities should try to strike the right balance
between the utility cost and the risk cost (if spare units are not there).
PAGE 27

29. Advantages of Auto Transformer:







Its efficiency is more when compared with the conventional ones.
Its size is relatively very smaller.
Voltage regulation of autotransformer is much better.
Lower cost.
Low requirements of excitation current.
Less copper is used in its design and construction.
In conventional transformer the voltage step up or step down value is fixed while in
autotransformer, we can vary the output voltage as per out requirements and can smoothly
increase or decrease its value as per our requirement.
Applications:



Used in both Synchronous Motor and Induction Motor.
Used in electrical apparatus testing labs since the voltage can be smoothly and
continuously varied.
They find application as boosters in AC feeders to increase the voltage levels.
Generating Transformer (GT):
This is a type of Power Transformer where the LV winding is connected to the generator
through the bus duct and HV winding to the transmission system. In addition to the
features of Power Transformer, our Generator Transformer is designed to withstand over
voltage caused by sudden load throw off from the generator. It is built as a single or three
phase unit and located in power stations.
Normally generating voltage is 15.75KV from generator. If we want to transmit that power
to 2220KV bus bar. This voltage must be stepped up, otherwise if we transmit at same
voltage level as generation voltages that is associated with high transmission loss so the
transformer which is used at generator terminal for stepping up the voltage is called
Generating Transformer.
SPECIFICATION OF GT:
MAKER
BHEL
MVA
HV- 150/200/250
LV- 150/200/250
VOLTS
HV- 245 KV
LV- 15.75 KV
RATED CURRENT
HV- 151/482/602
LV- 3505/7340/9175
PHASE
3
FREQUENCY
50
TYPE OF COOLING
OFAF/ONAF
PAGE 28

30. Station Service Transformer (SST):
Station service transformers (SSVTs) are intended to provide low voltage control power for
substations, cell tower installations, and at switching stations by tapping directly from the high
voltage line (220 KV bus bar).
Solidly-Earthed: The typical SST’s secondary fault levels are in the order of thousands of kVA.
Earth-fault currents resulting from solidly-earthed neutrals are high enough to operate fuses and
circuit breakers protecting low voltage cables and utilizing apparatus. Separate earth-fault
protection devices are not necessary. Except when fault currents are too low.
SPECIFICATION OF SST:
MAKER
MVA
BHEL
HV- 31.5/25.2
LV- 31.5/25.2
VOLTS
HV- 230 KV TV- 11KV LV- 6.9KV
RATED CURRENT
HV- 79.1 A TV- 551.1A LV-2635.8A
PHASE
3
FREQUENCY(Hz)
50
TYPE OF COOLING
ONAF/ONAN
Unit Auxiliary Transformer (UAT):
The Unit Auxiliary Transformer is the Power Transformer that provides power to the auxiliary
equipment of a power generating station during its normal operation. This transformer is
connected directly to the generator output by a tap-off of the isolated phase bus duct and thus
becomes cheapest source of power to the generating station.
It is generally a three-winding transformer i.e. one primary and two separate secondary windings.
Primary winding of UAT is equal to the main generator voltage rating. The secondary windings can
have same or different voltages i.e. generally 11 KV and or 6.9 KV as per plant layout.
SPECIFICATION OF UAT:
MAKER
MVA
VOLTS
RATED CURRENT
ATLANTA ELECTRICALS PVT. LTD.
12.5/16
HV- 15750 LV- 6900
HV- 458.2/586.5 LV- 1045.9/1338.8
PHASE
3
FREQUENCY(Hz)
50
TYPE OF COOLING
ONAN/ONAF
PAGE 29

31. Transformer Cooling:
The load that a transformer carries without heat damage can be increased by using an adequate
cooling system. This is due to the fact that a transformer’s loading capacity is partly decided by its
ability to dissipate heat.
1.
2.
3.
Dry Type Cooling
Air Forced/ Air Naturel (AF/AN): Transformer’s temperature is being kept at acceptable
levels by forced/naturel air from a fan/air circulation. Cooling fins are attached to increase
the surface area of heat radiation.
Oil Forced/ Oil Naturel (OF/ ON): Oil are used in transformer to provided insulation
and as a coolant agent. If the oil is circulated by pump than it is known as Oil Forced
cooling system, otherwise Oil Naturel Cooling System.
In MTPS naturally ONAN, ONAF, OFAN, OFAF and dry cooling system are used for
transformer cooling purpose.
PAGE 30

32. AC Power Flow in Power Station:
From the above diagram we can clearly see that there are mainly four voltage steps used in MTPS:




15.75 KV Generated Voltage
220 KV Busbar Voltage
6.6 KV for many types of high voltage drives in power station. (Such as Boiler Feed Pump
(3500KV))
415 Volts for different low voltage drive & all sorts of common application (like lights, etc.)
DC Power Flow:
In MTPS mainly three steps of DC Voltages are used:



310 volt DC is used for field excitation purpose of Alternator. This is controlled by AVR. By
means of static or brushless excitation system DC power is delivered to the rotating field of
Alternator. To get desired output voltage of alternator excitation voltage may vary.
220 V DC is used for operating all types of circuit breaker/ switchgear and some drive
(motor). In circuit breaker the auxiliary circuit and the motor drives is run by 220 V DC.
Some Regulator and motor (like seal oil pump) is run by this voltage.
And, 24V DC is used for all types of signaling system. All types of indicator, alarm is run by
24V DC supply.
PAGE 31

33. Switchyard Section:
A switchyard is essentially a hub for electrical power sources. For instance, a switchyard will exist at
a generating station to coordinate the exchange of power between the generators and the
transmission lines in the area. A switchyard will also exist when high voltage lines need to be
converted to lower voltage for distribution to consumers. Here in MTPS there is a big switch yard
section for the units one to six, and also for seven & eight there also a switch yard. Some of the
operation of the components of the switch yard is sometimes done from the control rooms of
respective units. That is the switch yard under each unit is sometimes control from the control
rooms of each unit respectively.
220 KV Switchyard section of MTPS, DVC
A switchyard may be considered as a junction point where electrical power is coming in from one
or more sources and is going out through one or more circuits. This junction point is in the form of
a high capacity conductor spread from one end to the other end of the yard. As the switchyard
handles large amount of power, it is necessary that it remains secure and serviceable to supply the
outgoing transmission feeder seven under conditions of major equipment or bus failure. There are
different schemes available for bus bar and associated equipment connection to facilitate switching
operation. The important points which dictate the choice of bus switching scheme are –
a)
b)
c)
d)
e)
f)
g)
Operational flexibility
Ease of maintenance
System security
Ease of sectionalizing
Simplicity of protection scheme
Installation cost and land requirement
Ease of extension in future.
PAGE 32

34. 220kV switchyard of M.T.P.S, DVC
PAGE 33

35. The components of a switchyard are as follows:
 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.
 Isolator: Isolators are switches which isolate the circuit at times and thus serve the
purpose of protection during off load operation.
 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.
 Potential Transformer: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.
 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)
PAGE 34

36. (1-Main tank 2-Radiator 3-Reservoir tank 4-Bushing 5-WTI & OTI Index 6-Breather 7Buccholz relay)
 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.
The figure shows a complete bay for 220kV switchyard:
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.
PAGE 35

37. The figure shows the power flow diagram of 33kV switchyard:
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 earthling 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.
PAGE 36

38. Some Pumps and Motors used in MTPS:
 Pumps:




Service water pump- 360Kw
Primary air fan(PA fan)- 800Kw
Coal mill motor- 2250Kw
Condense extraction pump- 500Kw
 Motors:




Boiler feed pump motor- 3500Kw
ID fan motor- 1500Kw
FD fan motor- 1000Kw
CW pump motor- 1200Kw
Switchgear:
In an electric power system, switchgear is the combination of electrical disconnect switches, fuses
or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used
both to de-energize equipment to allow work to be done and to clear faults downstream. This type
of equipment is important because it is directly linked to the reliability of the electricity supply.
Typically, the switchgear in substations is located on both the high voltage and the low voltage side
of large potential transformers may be located in a building, with medium-voltage circuit breakers
for distribution circuits, along with metering, control, and protection equipment. For industrial
applications, a transformer and switchgear line-up may be combined in one housing, called a
unitized substation or USS.
Types:
1. Oil: Oil Circuit breakers rely upon vaporization of some of the oil to blast a jet of oil
through the arc.
2. Gas:Gas (SF6) circuit breakers sometimes stretch the arc using a magnetic field, and then
rely upon the dielectric strength of the SF 6to quench the stretched arc.
3. Vacuum:Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other
than the contact material), so the arc quenches when it is stretched by a small amount (<23 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear
to 35,000 volts. Unlike the other types, they are inherently unsuitable for interrupting DC
faults.
4. Air:Air circuit breakers may use compressed air (puff) or the magnetic force of the arc
itself to elongate the arc. As the length of the sustainable arc is dependent on the available
voltage, the elongated arc will eventually exhaust itself.
PAGE 37

39. Uses:
Basic use of switchgear is protection, which is interruption of short-circuit and overload fault
currents while maintaining service to unaffected circuits. Switchgear also provides isolation of
circuits from power supplies. Switchgear is also used to enhance system availability by allowing
more than one source to feed a load.
Specifications:
SULPHUR-HEXAFLUORIDE CIRCUIT BREAKER
Rated Voltage
: 6.6 KV,
Rated Pressure of SF6
: 3.4 bar abs
Rated Current
: 800 A
Motor Supply Voltage
: 220 V/D.C.
Rated Frequency
: 50 Hz
Auxiliary Circuit
: 220 V/D.C.
Rated Peak Making Current
: 130vKV
Trip/ Closed Coil
: 220V/D.C.
Rated Braking Current
: 40 KA
Rated Short Time Current for 3 sec: 40 KA
Maker
:
NGEF in technical collaboration with ABB SPACE Italy
Note:Vacuum circuit breakers of Siemens instead of NGEF are incorporated in MTPS.
Generator Protection
 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.
 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.
 Over voltage protection:The over voltage at the generator terminals may be caused 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
PAGE 38

40. no special protection against generator high voltage may be needed. Further protection
provided against high magnetic flux takes care of dangerous increase of voltage.
 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.
 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:
 Differential protection:The protection is used for detection of internal faults in a
specified zone defined by the CTs supplying the differential relay. For a 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.
 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.
 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.
 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.
PAGE 39

41.  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.
 Rotor earth fault protection: Normally a single rotor earth fault is not as 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.
Motors for Thermal Power Plant
All the motors in Thermal Power Stations shall be of the 3-ph. A.C. squirrel cage type except for
some auxiliaries, which are emergent in nature, for which DC motors shall be used. For some small
valves, single phase motors may be used. All A.C. motors shall be suitable for direct on line starting.
Battery Bank
Normally D.C. power is supplied by the float charger and
the batteries are kept in float condition at 2.15 V per cell to
avoid discharging. The charger consists of silicon diode or
thyristor rectifiers preferably working on 3 ph. 415 V
supply in conjunction with an automatic voltage regulator.
When there is a failure in the A.C. supply the batteries will
come into operation and in this process the batteries run
down within few hours. After normalization of A.C. power
the batteries are charged quickly by using the boost
charger at 2.75 V per cell. During this time the float
charger is isolated and load is connected through the tap
off point. After normalization of battery voltage these are
again put back into the float charging mode. The output
from the battery as well as the charger is connected to the
D.C. distribution board. From D.C. distribution board
power supply is distributed to different circuits. D.C.
system being at the core of the protection and control
mechanism very often two 100% capacity boards with
individual chargers and battery sets are used from the consideration of the reliability and
maintenance facility. These two boards are interconnected by suitable tie lines.
PAGE 40

42. DVC: Transmission & Distribution Network
Charged with the responsibilities of providing electricity, the vital input for industrial growth in the
resource-rich Damodar Valley region, DVC over the last 60 years has developed a big and robust
transmission network consisting of 132 KV and 220 KV grids. DVC grids operated in unison with the
Eastern Regional grid through 132 KV and 220 KV Tie lines. All the power stations and Sub-stations
of DVC are connected with the DVC grids. DVC power consumers are provided supply at 33 KV, 132
KV and 220 KV pressure.
DVC Transmission Lines is service at a Glance
States
Transmission line length in Km
220 KV
132 KV
Jharkhand
780
2533
West Bengal
1037
1096
Orissa
35
-
TOTAL
1852
3629
Interconnecting Tie Lines with DVC Network
Tie-Line
Voltage
Other Utility
Length(Km)
D/C DTPS- Bidhannagar
220KV
WBSEB
34.52
S/C Jamshedpur- Joda
220KV
GRIDCO
135.00
D/C Kalyaneswari- Pithakari
220KV
PGCIL
15.2
D/C Parulia- Parulia
220KV
PGCIL
2.00
D/C Dhanbad- Pithakari
220KV
PGCIL
103.4
S/C CTPS- STPS*
220KV
WBSEB
12.64
S/C Barhi- Biharsarif
132KV
JSEB
95.00
S/C Brhi- Rajgir
132KV
JSEB
80.00
S/C Maithon- Sultanganj
132KV
JSEB
107.00
D/C Patratu- PTPS
132KV
JSEB
20.00
S/C Chandil- Manique
132KV
JSEB
3.00
S/C Kolaghat- Kolaghat
132KV
WBSEB
3.00
S/C Kharagppur-Kharagpur
132KV
WBSEB
1.00
S/C Purulia- Purulia
132KV
WBSEB
0.00
*Out of service
PAGE 41

43. DVC Substations in service (Nos.) at a glance
State
33KV
132KV
220KV
Jharkhand
9
18
5
West Bengal
7
10
5
Total
16
28
10
DVC Grid Map:
Single Line Diagram of 220KV MTPS Grid:
PAGE 42

44. Conclusion
The vocational training had been concluded in a very efficient way. We have acquired thorough
knowledge about generation, transmission and distribution of power. Mejia Thermal Power
Station, being one of the largest power station in the Eastern India, had been acting as a pioneer in
power generation over a decade.
MTPS is a part of Damodar Valley Corporation which governs the power generation for Industrial
and Commercial requirement and attenuate the economic as well as social well-being of
humankind.
We have carried out this training under well experienced and highly qualified engineers of MTPS,
DVC of various departments’ viz. mechanical, electrical, Chemical and Control & Instrumentation
depts. The work culture of DVC is very noticeable and very energetic. Although this is an old power
plant, the machines and entire instruments are functioning very well due to proper maintenance
and skill in handling them. I was able to acquire practical knowledge of the industry and about
some theoretical engineering studies.
The Project Report has covered the mechanical overview, electrical overview, various cycles and
processes (viz. Steam Generation, Turbo Generation and Balance of Plant) of power generation and
details of control and instrumentation required in thermal power plant.
PAGE 43

45. Bibliography






www.google.com
www.dvcindia.org
www.wikipedia.org
Power Plant Engineering by P.K.Nag
Theory &Performance of Electrical Machine by J.B.Gupta
AC & DC Machines by B.L.THERAJA & A.K.THERAJA
Etc…
PAGE 44