This document provides a synopsis on the NTPC Vindhyachal Thermal Power Station located in Singrauli District, Madhya Pradesh, India. The power station has a total installed capacity of 4,260 MW across 5 stages. It sources coal from nearby Nigahi coal mines and water from the Rihand reservoir. Key details provided include plant configuration, commissioning timelines of different stages, transmission network, power allocation to states, operational performance highlights, safety awards received, and coal and ash utilization. The document also includes basic information about factors considered for locating a thermal power plant and definitions of plant load factor and power purchase agreement.

1. VocationalTrainingReport
On
Synopsis on Thermal Power Station
At
NTPC Vindhyachal
In partialfulfilmentof the requirements
For the award of the degree
BACHELOR OF TECHNOLOGY
IN
Electrical Engineering
By
VIJAY CHOUDHARY
(Sch. No. 121113013)
Under the Guidance
Of
Mr. ATUL MARKHEDKAR
AGM – EMD, NTPC VINDYANAGAR
Department of Electrical Engineering
Maulana Azad National Institute of Technology,
Bhopal (M.P.), India
MAY-JUNE 2015

2. Vocational Training Report
ON
Synopsis on Thermal Power Station
@
NTPC Vindhyachal
Under Guidance of:
Mr. A. MARKHEDKAR
Additional General Manager
Electrical Maintenance Department
PREPARED BY-
VIJAY CHOUDHARY
MANIT, BHOPAL
Training MAY-JUNE 2015

3. ACKNOWLEDGEMENT
With profound respect and gratitude, I take opportunity to convey my
thanks to our alumani Mr. Ankit Jain (Deputy H.R.-EDC) Sir for
permitting me to complete my training in NTPC Ltd. and to be the part
of this esteemed organization.
I extend my heartfelt thanks to MR. A. MARKHEDKAR Sir for providing
me the proper guidance during my training period in Vindhayachal
Stage I.
I would also thank Mr. Vikas Gupta (Deputy Manager), Mr. Charan Das
Bankoliya, Mr. Rajesh kumar Verma, for helping me with different aspects
of the power plant.
I’m extremely grateful to all- the operation and guidance that has helped
me a lot during the course of training. I have learnt a lot under them and
i will always be indebted to them for this value addition in me.
At last I would like to convey my thanks to all the members of the
Electrical Maintenance Dept., and I am are forever indebted to the
omnipotent and to my parents for their cheerful encouragement,
unfailing patience and consistent support.
VIJAY CHOUDHARY
VOCATIONAL TRAINEE
15
th
May –14
th
June 2015
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5. CONTENT
S.NO. TOPICS PAGE NO
1. Introduction: NTPC Ltd 1
2 NTPC Vindhyachal 2
3. Power Plant Basics 4
4. Coal Handling Plant 9
5. Working Of Steam Power Plant 11
6. Basic Cycles of Power Plant 14
7. Generator & it’s Auxiliaries 26
8. Excitation System 28
9. Protection of Generator 32
10. Switchgear 40
11. Switchyard 47
12. Switchyard Equipment’s 49
13. Switchyard Protection 56
14. Essential Quality of Electrical Protection 56
15. HVDC Back To Back System 57
16. Water Treatment Plant Storage 58
17. Conclusion 59
18. Bibliography 60
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6. INTRODUCTION: NTPC Ltd.
 NTPC Limited (formerly National Thermal Power Corporation) is the 
largest Indian state-owned electric utilities company based in New Delhi, India. 










It is listed in Forbes Global 2000 for 2012 ranked at 337th in the world. 
SERVICE – Electricity generation and distribution natural gas
exploration, production, transportation and distribution 
PRODUCT - electrical power, natural gas 
REVENUE- 690.36 billion (US$13 billion) (2011–12) 
NET INCOME - 98.14 billion (US$1.8 billion)(2011–12) 
 EMPLOYEE-26,000 (2012) 


 It is an Indian public sector company listed on the Bombay Stock Exchange in
which at present the Government of India holds 84.5% (after divestment of 

the stake by Indian government on 19 October 2009) of its equity. 
 With an electric power generating capacity of 41,184 MW, NTPC has embarked on
plans to become a 128,000 MW company by 2032.  
On 21 May 2010, NTPC was conferred Maharatna status by the Union Government
of India.
 NTPC's core business is engineering, construction and operation of power
generating plants and providing consultancy to power utilities in India and 

abroad. 
 The total installed capacity of the company is 36,514 MW (including Joint
Ventures) with 16 coal-based and 7 gas-based stations, located across the
country. In addition under JVs (joint ventures), six stations are coal-based, and 

another station uses naphtha/ LNG as fuel. 
 By 2017, the power generation portfolio is expected to have a diversified fuel mix 




with coal-based capacity of around 27,535 MW, 3,955 MW through gas, 1,328 MW
through hydro generation, about 1,400 MW from nuclear sources and around
1,000 MW from Renewable Energy Sources (RES). 
NTPC’s share at 31 Mar 2001 of the total installed capacity of the country was
24.51% and it generated 29.68% of the power of the country in 2008–09. Every
fourth home in India is lit by NTPC. 
 By approval of the Central Government under section 21 of the Companies Act,
1956, the name of the Company "National Thermal Power Corporation Limited"
has been changed to "NTPC Limited" with effect from 28 October 2005. 

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7. 

8. NTPC-Vindhyachal
STATION PROFILE
LOCATION:
Vindhyachal station of NTPC is located at Vindhyanagar in Singrauli District of MP state.
The station is situated on thebank ofGovindVallabh Pant Sagarpopularlyknown asRihand
reservoir. Distance of station from Varanasi in UP and Sidhi in MP is about 240 Kms. and
100 Kms. Respectively.
CAPACITY (4260 MW):
STAGE NUMBER CAPACITY(MW) COMMISSIONED
STAGE I 6 X 210 = 1260 MW 10th June’87
’88,’89,’89,
(UNIT II,III,IV,V&VI)
STAGE II 2 X 500 = 1000 MW 1999 & 2000
(UNIT VII & VIII)
STAGE III 2 X 500 = 1000 MW 27th July’06
(UNIT IX &X)
STAGE IV 2 X 500 = 1000 MW 2013& 2014
STAGE V 500 MW (under construction)
 Stage-I & Stage-II were totally declared commercial in Feb’92 and Oct’2000 respectively. 
 Stage-III– Unit-9 Synchronized on 27th Jul 2006 and became commercial from 1st Dec
2006. Unit-10 was synchronized on 8th Mar 2007 and unit became commercial from 15th
Jul 2007. 
 Stage-IV-Unit- 11& 12 were totally declared commercial in Mar’13 and Mar’14
respectively.
LAND:
Total land acquired 6178 acres.
WATER:
Water for NTPC Vindhyachal is drawn from NTPC Singrauli station discharge channel
which in turn takes it from Rihand reservoir. A total commitment of 190 cusecs of Make -
up water is already available which covers requirement for Stage-I, II & III. Closed loop
cooling water system using Cooling Towers has been adopted at Vindhyachal Station.
COAL:
The coal linkage for this station is from the Nigahi Coal Mines of NCL. From there, the coal
is transported by Merry Go Round (MGR) transportation system (22 Kms length with
double track) owned and operated by NTPC. The requirement of coal per year for use in
stage- I, II and stage-III is around 17.1 million MT.
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9. STAGE WISE COMMISSIONING
 STAGE I - Oct. 1987-Feb.1991 (7th Plan) 
 STAGE II - Mar. 1999-Feb. 2000 (9th Plan) 
 STAGE III –Jul. 2006 -Mar.2007 (10th Plan) 
 STAGE IV-Mar. 2013-Mar.2014(11th Plan) 
ASSOCIATED TRANSMISSION SYSTEM:
Power generated by NTPC-Vindhyachal flows to the Western Region Grid. The power is
shared between various states of Western Region. Transmission lines connected to
Vindhyachal Station are as follows –
  400 KV –4lines to Jabalpur  
 HVDC –Link between Western –Northern Region  
 400 KV –Link line to Korba  
  400 KV –4 Lines to Satna –Bina  
 132 KV –2 Lines to Waidhan  
ALLOCATION OF POWER:
The percentage sharing of power from 2260 MW (Stage-I & II) of Vindhyachal between
the beneficiary states is as below –
 Madhya Pradesh 29.5 %
 Maharashtra 36.1 %
 Chhattisgarh 3.4 %
 Gujrat 23.6 %
 Goa, Daman & Diu, Dadra, Nagar Haweli 7.4 %
The allocation of power from 1000 MW of stage-III is as below
 Madhya Pradesh 23.1 %
 Maharastra 31.9 %
 Gujrat 23.9 %
 Chhattisgarh 4.2 %
 Goa, Daman & Diu, Dadra, Nagar Haweli 1.9 %
 Unallocated 15.0 %
PERFORMANCE HIGHLIGHTS:
Some of the major performance highlights are as below –
 Station qualified for meritorious productivity award of Govt. of India several times.  
 Vindhyachal stood 4th in the Country in 1998-99 with a PLF of 90 %  
  Vindhyachalstood 5th in the Country in 1999-2000 with a PLF of 88%  
 Vindhyachal stood 12th in the country in 2002-03 with a PLF of 85 %  
  Vindhyachal stood18thin the country in2003-04 witha PLF of 82 %  
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10.  Vindhyachal stood 5th in the country in 2005-06 with a PLF of 92 %
 Vindhyachal stood 8th in the country in 2006-07 with a PLF of 92 %
 Uninterrupted running of Vindhyachal Unit #3 (210 MW) for 559 days is a
new national record.  
TREE PLANTATION:
Due emphasis has been given on Tree Plantation at NTPC-Vindhyachal. So far more than
17.38 lakh trees have been planted in and around the station. The work of tree plantation
is being taken as one of the targets every year and is being monitored regularly.
ASH UTILIZATION:
2006-2007 21, 04632 MT 56.00%
SAFETY & OTHER AWARDS TO STATION:
 1987 –National Safety Council Award  
 1998 –British Safety Council Award  
 1999 –British Safety Council Award  
  1999 –NationalSafety Award  
 2000 –National Safety Award  
 2003 –Golden Globe Award for Environment (By NTPC)  
 2004 –Green-tech Safety award  
  2005 − CII EXIM Business Excellence Award  
 2006 –Green-tech Silver Award for Environment  

 2007- National award foreconomics of quality (dl shahcommendationaward) by Hon’ablePresidentof
India on9th Feb’07
 2008- National award for economics of quality (dl shah award) on 16th Feb’ 08 
 2008- National award for economics of quality (dl shah commendation award) on
16th Feb’ 08  
POWER PLANT BASICS
1. LOCATING A THERMAL POWER PLANT
(1) SITE REQUIREMENT
Adequate Land–Lease from forest department.
For Each 1000MW = 90 to 200 Acres of land.
(2) GEOLOGY
Soil Requirement
~ 4 ~

11. Which can bear Heavy structures.
(3) WATER REQUIREMENT For
Boiler 3 to 4 Tons/hr./MW.
For cooling once through -20000m3/hr./100MW.
(4) COAL REQUIREMENT: NIGAHI MINE S- CLOSE TO 60000 TONS/DAY.
(5) TRANSPORT
(6) DISPOSAL OF ASH- 30% ASH
(7) TRANSMISION OF POWER
(8) PROXIMITY TO AIR FIELD
(9) FISHERIES AND MARINE LIFE. 10C
(10) PERSONNEL REQUIREMENT
2. PLANT LOADING FACTOR (PLF)
It is defined as the ratio of total generation of the power plant to its installed capacity. Since
its inception, NTPC has always maintained high values of PLF close to 85% - 95% which
has increased the overall power production capability of the plant.
3. POWER PURCHASE AGREEMENT (PPA)
Before setting up of a power plant, MoU’s are interested in purchasing the power from the
plant. A fixed amount is allotted and the concerned state has to pay the cost accordingly
even if the demand is less.
~ 5 ~

12. BASIC LAYOUT OF A COAL FIRED PLANT
The basic building block of a coal fired plant is steam, which is generated from properly
treated and De-Mineralized water (DM water), supplied by CW (Circulating Water) pump
house. The coal is finely powered to increase its surface area for efficient firing and this
process is called pulverization and it is carried out in Coal Handling Plant (CHP) located
near MGR (Merry Go Round) system of NTPC. The Pulverized coal is then sent to bunkers
via conveyor belts and is then sent to the furnace via a typical air draft system discussed at
later stage.
The firing ofcoalinside furnacemaintains it to a veryhigh temperatureandthis heat energy
is converted into pressure energy in the form of super heated steam extracted from the DM
water flowing inside the water walls located in the boiler which is in turn embedded into
the furnace.
This super heated steam does the actual work on turbine blades which reduces its
temperature and pressure and converts the pressure(&heat) energy into kinetic energy of
moving blades. The exhaust steam is re circulated via condenser which would be discussed
later. Now the rotational kinetic energy of turbine is converted into electrical energy using
Turbo Generator (TG) and sent to the distribution sector (Switchyard) via Generator
Transformer(GT). The powerflowand all the necessaryprotectionregardingloaddispatch
is commissioned in Switchyard.
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13. COMPLETE DESCRIPTION OF POWER PLANT
COAL TRANSPORTATION & HANDLING
Coal is a heterogeneous solid fuel and Composed of two types
of material Coal = Combustible + Non- combustible
(Maceral) (Mineral)
1. Maceral is the coaly matter produces heat on coal combustion C
(coal) + O2 (Air) = CO2 +Heat (exothermic reaction)
Heat→ Steam raising → Mechanical energy →Ele
2. Second part mineral is undesirable one and on combustion forms ash.
Ash = thermally transformed minerals (Oxides)
WHY COAL QUALITY?
•Coal Quality affects the performance of a power station starting from Milling system to
ESP
•Coal quality has a significant bearing on design of steam generator and on types & size
of auxiliaries.
•Knowledge of coal quality is Essential for its Efficient utilization
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14. •Correct Assessment of Coal quality is Essential for Correct Performance Assessment.
Grade Useful Heat Value Corresponding Gross Calorific
(UHV) (Kcal/Kg) Ash% + Moisture Value GCV (Kcal/
% at (60% RH & Kg) (at 5%
40O C) moisture level)
A Exceeding 6200 Not exceeding 19.5 Exceeding 6454
B Exceeding 5600 but 19.6 to 23.8 Exceeding 6049 but
not exceeding 6200 not exceeding 6454
C Exceeding 4940 but 23.9 to 28.6 Exceeding 5597 but
not exceeding 5600 not exceeding.
6049
D Exceeding 4200 but 28.7 to 34.0 Exceeding 5089 but
not exceeding 4940 not Exceeding 5597
E Exceeding 3360 but 34.1 to 40.0 Exceeding 4324 but
not exceeding 4200 not exceeding 5089
F Exceeding 2400 but 40.1 to 47.0 Exceeding 3865 but
not exceeding 3360 not exceeding.
4324
G Exceeding 1300 but 47.1 to 55.0 Exceeding 3113
not exceeding 2400
MGR
MGR is merry-go-round system of NTPC for captive transportation of coal from the mine
end to the power plant. MGR of NTPC-VINDHYACHAL has its own locomotives and wagons.
Various rakes are deployed for transportation of around 30,000 MT/day of coal. One rake
consists of one locomotive and up to 33 wagons. Due to configuration of tracks at track
hoppers end and for safety reason more than 33 wagons are never deployed in a rake.
Signalling is also provided for safety of the rake movement. Operational activities of MGR,
which are required for bringing coal from mine end to track hopper of NTPC-Vindhyachal
are identified and planned in accordance.
For unloading of coal from the locomotive, two methods are deployed-
 Manual via track hopper 

 Wagon Tippler 
Track hoppers are conical arrangements for inlet of coal inside the conveyor belt
arrangement system via paddle feeders which directs the flow of coal to conveyors. Track
Hopper, normally of 200-250m length. Manual labor required for coal scavenging.
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15. In wagon tippler arrangement the wagons are jacked at once and turned down into
the track hopper. No manual labor required.
COAL HANDLING PLANT
The coal is received at track hopper of CHP through the merry go round system used for
coal transportation. Coal flows through paddle feeders, belt conveyors, vibro feeder /
vibrating screen to the crusher where it undergoes size reduction (-20 mm size). The
crushed coal is transported through different conveyors and trippers to the respective unit
bunkers. The coal crushed in excess of the requirement is stacked at stockyard of CHP
through stacker / reclaimers.
Whenever required by system, the coal is reclaimed and fed to unit bunkers through
stacker / reclaimers. Cage bar / cage screen are checked regularly to ensure that crusher
output is always maintained as per the requirement stated above. In case bigger size coal
is found, that crusher is offloaded and inspected for rectification.
BUNKERING:
Uncrushed coal from track hopper is fed to crusher, where it under goes a size reduction,
and then it is fed to the bunkers through various conveyors and trippers. The sizes of coal
feeding to the bunkers are being checked manually by physical inspection.
STACKING:
The coal which comes from mine through the MGR system is crushed and the crushed coal
from crusher is diverted to the stacker-cum-reclaimers through concerned conveyors if
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16. all unit bunkers level is normal. The coal is stacked in 05 nos. available yards in a planned
manner by proper dozing and water spraying process.
RECLAIMING:
Coal is reclaimed from stack yard with the help of stacker-cum-reclaimer and fed to the
bunkers as per requirement of the process or whenever
The conveyor belt motors are continuously monitored for over/under loading conditions
via SCADA interface panel from CHP control room. Magnetic separators and various types
of protection limit switches are present inside the conveyor belt region for monitoring.
Transfer points (TP) are used for connecting various conveyor regions and Penthouse
contains magnetic separators and metal detectors in the raw coal. The
Coal is then crushed in CRUSHER HOUSE and sent to Bunkers via other set of conveyor bel

17. WORKING OF STEAM POWER PLANT
  Coal is burnt in a boiler, which converts water into steam.  
  The steam is expanded in a turbine used todrive alternator.  
 The steam expanded is condensed in a condenser to be feed into the boiler again.  
SCHEMATIC ARRANGEMENT OF COAL STEAM POWER PLANT
Steam generating equipment includes:
1. BOILER
A boiler is closed vessel in which water is converted into steam by utilizing the
heat of coal combustion. Steam boilers are broadly classified into following two
types:
 Water tube boilers 
In a water tube boiler, water flows through the tubes and the hot gases of
combustion flow over these tubes. Water-tube boilers are used for high-
pressure boilers
 Fire tube boiler 
In a fire tube boiler, the hot products of combustion pass through the tubes
surrounded by water. The heated water then rises into the steam drum. Here,
saturated steam is drawn off the top of the drum. The steam will reenter the
furnace in through a superheater in order to become superheated. Superheated
steam is used in driving turbines. Since water droplets can severely damage
turbine blades, steam is superheated to 730°F (390°C) or higher in order to
ensure that there is no water entrained in the steam.
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18. 2. SUPER HEATER
  A device which removes last traces of moisture.  
 It helps in reduction in requirement of steam quantity.  
 Steam being dry reduces the mechanical resistance of turbine.  
 No corrosion at the turbine blades  

3. ECONOMISER AND AIR HEATER
 They are such devices which recover the heat from the flue gases on their
way to chimney and raise the temperature of feed water.  
  Economizer raises boiler efficiency.  

 Air Pre-heaters recover the heat from the flue gases leaving the economizer
and heat the incoming air required for combustion  

4. CONDENSER
  Whichcondenses the steam at the exhaust of turbine  

 It creates a very low pressure at the exhaust of turbine, this helps in
converting heat energy of steam into mechanical energy in the prime mover.
 
  The condensed steam can be used as feed water to the boiler.  

 It creates a very low pressure at the exhaust of turbine, this helps in
converting heat energy of steam into mechanical energy in the prime mover.
 
 The condensed steam can be used as feed water to the boiler.  

5. PRIME MOVER (TURBINE)
 A steam turbine is a mechanical device that extracts thermal energy from 
 pressurized steam, and converts it into mechanicalenergy.  

 About 86% of all electric generation in the world is by use of steam turbines.
 
 It has almost completely replaced the reciprocating piston steam engine.  

6. COOLING TOWER
 Remove heat from the water discharged from the condenser so that the 
 water can be discharged to the river or re circulated and reused.  
 Air can be circulated in the cooling towers through natural draft and
mechanical draft.  
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19. ARRANGEMENT OF STEA M POWER PLANT
Induced Draft Forced Draft
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20. ELECTROSTATIC PRECIPITATOR
Indian coal contains about 30% of ash. The hourly consumption of coal of a 200 MW unit is
about 110 tons. With this, the hourly production of ash will be 33 tons. If such large amount
of ash is discharge in atmosphere, it will create heavy air pollution thereby
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21. resulting health hazards. Hence it is necessary to precipitate dust and ash of the flue gases.
Precipitation of ash has another advantage too. It protects the wear and erosion of ID fan.
To achieve the above objectives, Electrostatic Precipitator (ESP) is used. As they are
efficient in precipitating particle form submicron to large size they are preferred to
mechanical precipitation.
CONSTRUCTION:
An ESP has series of collecting and emitting electrons in a chamber collecting electrodes
aresteel plates while emitting electrodesarethin wire of 2.5mm diameter and helical form.
Entire ESP is a hanging structure hence the electrodes are hung on shock bars in an
alternative manner.
It has a series of rapping hammer mounted on a single shaft device by a motor with the
help of a gear box at a speed of 1.2 rpm. At the inlet of the chamber there are distributor
screens that distribute the gas uniformly throughout the chamber.
There are transformer and rectifiers located at the roof of chamber. Hopper and flushing
system form the base of chamber.
WORKING
Flue gases enter the chamber through distributor screen and get uniformly distributed.
High voltage of about 40 to 70 KV form the transformer is fed to rectifier. Here ac is
converted to dc. The negative polarity of this dc is applied across the emitting electrode
while the positive polarity is applied across the collecting electrodes. This high voltage
produces corona effect negative (–ve) ions from emitting electrode move to collecting
electrode. During their motion, they collide with ash particles and transfer their charge. On
gaining this charge,ashparticles too move to collecting electrode and stock to them. Similar
is the case with positive (+ve) ions that moves in opposite direction.
The rapping hammers hit the shock bars periodically and dislodge the collected dust from
it. This dust fall into hopper and passes to flushing system. Here it is mixed with water to
form slurry which is passed to AHP.Efficiency of ESP is approximately 99.8%.
1. Side view of electrostatic precipitator
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22. BASIC CYCLES OF A POWER PLANT
The power plant now can be subdivided into a number of closed process cycles which
are as follows-
1. Coal cycle
2. Primary and Secondary Air draft cycle
3. Super Heated Main Steam Cycle
4. Circulating Water and Condensate cycle
5. Flue Gas Cycle.
COAL CYCLE
Now the basic inputs and requirements for proper burning of coal are
1. Pulverization of coal for increased surface area and easy flow into furnace.
2. Proper Ignition temperature and moisture free.
3. Air for complete combustion. Thus the required for burning of coal and conversion
of water into steam is covered under the above mentioned cycles.
TO FA AND FD
DRAUGHT SYSTEM
Raw Coal
Feeders

23. Bunkers are cylindrical storage tanks of crushed coal from CHP. The coal level is always
maintained within limits and is handled by conveyors whose rate can be controlled from
the CHP control room. For a 210MW stage at BTPS there are 10 bunkers and each bunker
is connected to RC feeder which is special type of motor arrangement for feeding properly
crushed coal into mill motors. The idea here is to reject any type of metallic or impurity or
unwanted substances from coal. A RC feeder consists of three rollers with a conveyor belt
in it, the amount once released from this feeder definitely goes into the furnace and the
amount is controlled via the speed of conveyor belt and two opening gates, one motorized
and one manual. There are 10 set of Mill Motors. Each mill motor contains a bowl and roller
arrangement for crushing of coal and this crushed coal is carried away to the furnace via
mix PA discussed at later stage.
RC FEEDER SPECIFICATIONS
Type SECO - 36'' Gravimetric (with Mechanic
Weighing)
Capacity Minimum - 11350 Kg/hr.
Maximum - 87820 Kg/hr.
Supplier SECO. U.S.A.
Density of material to be handled 720 to 1280 Kg/m
3
Drive Motor (KW) 5.6
Clean out motor (KW) 0.22
Power supply 415V, 3-phase, 50 Hz
Gear reduction 130.5,1 at 1375 rpm
Special features Free standing control cabinet Tropical
service, Eddy current clutch control,
water sprays Motion monitor, Purge air
valve.
MOTOR USED IN BOWL MILL
Manufacturer M/s Siemens West Germany/BHEL Bhopal.
Motor Type SQ – Motor
Standard continuous rating at 40
0C 560 KW
Derated rating for specified normal 525 KW
Rated voltage 6600 Volts
Minimum permissible starting voltage 90% rated
Rated speed 590 RPM
AIR DRAFTCYCLE
The Primary Air, Secondary Air & Flue gas System:
The PA needed to carry away the pulverized coal from the Pulverizes to furnace is
supplied by two numbers PA Fans. A portion of PA passes through APH where it picks
up the heat from flue gas and becomes hot PA.
~ 17 ~

24. FD SAP WIND B
PA
FANS
Cold
PAPH
MILPA
The SA which ensuresthecomplete combustion ofthe fuel in the furnaceis supplied by two
numbers Force Draught (FD) fans. The whole SA passes through APH & picks up heat from
flue gases & goes to wind box. From wind box it goes to furnace via SADC comprising of
FAD located at coal mill elevation which opens proportional to feeder speed. Auxiliary air
dampers which maintains furnace to wind box DP. Oil air dampers, which are open at the
oil elevation, are in-service proportional to the oil pressure. In case there is no oil firing,
these dampers behaves like Auxiliary air dampers.
In order to avoid the furnace getting subjected to the positive pressures, the flue gases
which results from the combustion of the coal are drawn out of the furnace via APH (Air
Pre Heaters) using two numbers ID fans, which discharges the flue gas to Chimney which
is further discussed in flue gas cycle.
The temperature of the air provided by PA Fan is controlled via cold PA extracted from the
PA line before APH, the cold PA is then mixed with Hot PA from PAPH and passed via bowl
mill motors creating primary air draft system.
~ 18 ~

25. Seal Air Fan:
These are used for supplying seal air to the mills to prevent ingress of coal dust into
gearbox lubrication oil. There are two fans per boiler.
Soot Blowers:
The soot blowers are used for efficient on -load cleaning of furnace, super heaters,
Reheaters and regenerative air heaters. There are three types of soot blowers provided in
the plant in requisite numbers. They are:
1. Long retractable soot blowers
2. Wall blower
3. Air heater blower
Superheated steam is tapped from the super heater for the purpose of soot blowing.
STEAM CYCLE
BOILER
Boiler can simply defined as the device where any liquid is boiled or Boiler may be defined
as a device that is used to transfer heat energy being produced by burning of fuel to liquid,
generally water, contended in it to cause its vaporization. Boiler, in simple
terms, can be called“Steam Generator”. The following are fact efficient combustion
usually referred as “The three T’s”.
a) Time –It will take a definite time to heat the fuel to its ignition temperature
and having ignited, it will also take time to burn.
b) Temperature –A fuel will not burn until it reaches its ignition temperature.
c) Turbulence –Turbulence is introduced to achieve a rapid relative motion
between the air and fuel particles
Block Diagram of Steam Cycle
~ 19 ~

26. COMPONENTS OF A BOILER
1. ECONOMISER
2. BOILERDRUM
3. DOWN COMERS
4. WATER WALL
5. PRIMERY SUPER HEATER
6. PLATEN SUPER HEATER
7. FINAL SUPER HEATER
8. RE-HEATER
9. BURNER
10. OIL GUNS
11. IGNITORS
12. BUCK STAYS
ECONOMISER
1. FORMED IN TWO STAGES - ECO I & II AND ECO III
2.
FORMS PART OF FEED WATER CIRCUIT
3.
PRE HEAT BOILER FEED WATER
4.
RECOVERY OF HEAT FROM FLUE GAS
5.
LOCATED INBOTTOM OF REAR PASS
6.
NO STEAM FORMATION
BOILER DRUM
1.
TO SEPARATE WATER FROM STEAM
2.
TO REMOVE DISSOLVED SOLIDS
3.
TO PROTECT WATER WALLS FROM STARVATION
4.
ACTS AS TEMPORARY PRESSURE RESERVOIR DURING TRANSIENT LOADS
WATER WALL

1. FORMS FURNACE ENCLOSURE 

2. GENERATION OF STEAM  
 3. PROVIDES SEALING TO FURNACE 












~ 20 ~

27. SUPER HEATER
RAISE STEAM TO HIGHER TEMPERATURE ARRANGED IN 3 STAGES

LTSH LOCATED ABOVE ECONOMISER



RADIANT PENDENT TYPE (DIV PANEL) ABOVE FURNACE 

 CONVECTIVE FINAL SUPER HEATER ABOVE FURNACE IN CONVECTIVE PATH 
RE HEATER

RE HEAT THE STEAM FROM HP TURBINE TO 540 DEG
 

COMPOSED OF THREE SECTIONS 

RADIANT WALL REHEATER ARRANGED IN FRONT & SIDE WATER WALLS 

REAR PENDANT SECTION ARRANGED ABOVE GOOSE NECK 


FRONT SECTION ARRANGED BETWEEN UPPER HEATER PLATEN & REAR WATER WALL
HANGER TUBES

~ 21 ~

28. The Main steam & Re-Heated steam System :
The heat produced by the combustion of the coal is used to generate the steam. The steam
is further heated in the super heaters & forms Main Steam. This main steam is delivered
to the Turbine through main steam (MS) lines in a controlled manner by means of Main
Steam Stop Valves & Control valves that are regulated by the TG Governing System. In
turbine the steam expands & converts Heat energy in to Mechanical energy.
In between the HP turbine & IP turbine the steam is again carried to the Boiler, where it is
reheated & delivered to the IP turbine in a controlled manner by means of RH steam stop
valves & control valves that are regulated by the TG Governing system
After the turbine, the steam goes to the condenser where it is condensed under deep
vacuum using CW. The condensate is collected in the Hot well
CIRCULATING WATER CYCLE
Condensate, Feed Water & Boiler Water system
The condensate from the hot well is extracted by CEP & is pumped, via LP Heaters where it
gets heated up, to the Deaerator. The condensate now becomes feed water & gets stored in
the Feed Storage Tank just below Deaerator. The BFP takes Suction from this Feed Storage
tank & pumps this feed water through HP heaters, feed control station & economizer to the
Boiler Drum, where it becomes Boiler Water. This boiler water goes to the boiler water
walls where it absorbs heat, transforms in to steam & return back to the Boiler drum. In
stage I boiler this circulation of boiler water is natural, whereas in stage III boiler it is
assisted by CW pumps.
~ 22 ~

29. CW System
CW system consists of CW pump house having CW pumps for supplying CW to the
condenser of stage III units through common CW duct & also for supplying raw water to
Auxiliary pond for miscellaneous use. Auxiliary Water pump house, which draws water
from Auxiliary pond & supplies for various purposes such as fire water system, raw water
supply for clarification plant etc. Clarification plant, where the raw water is clarified & is
fed to the clarified water tank. Clarified water pump house, where the clarified water is
pumped to supply it to generator gas coolers & other BCW system.
STEAM TURBINE
GENERAL:
At Vindhyachal Station 500 MW capacity turbines are of Kraft Werk Union (KWU -
Germany) design and supplied by BHEL. The turbine is condensing, tandem compounded,
horizontal, reheat type, single shaft machine. It has got separate high pressure,
intermediate and low pressure parts. The HP part is a cylinder and IP & LP parts are double
flow cylinders. The turbine rotor is rigidly coupled with each other and with generator
rotor.
HP turbine has throttle control. The stream is admitted through two combined stop and
control valves. The steam from reheaters is admitted to IP turbine through two combined
stop and control valves. Two crossover pipes connect IP and LP cylinder.
The entire turbine is provided with reaction blading. The moving blades of HPT, LPT and
front rows of LPT have inverted T roots and shrouded. The last stages of LPT are twisted;
drop forged moving blades with fir tree roots. They also have guide blades for proper
functioning. The TG unit is mounted on six bearings HPT rotor is mounted on two bearings,
a doublewedgedjournal bearingat the frontand combined thrust bearingadjacent to front
IP rotor coupling.
In the 500 MW KWU turbines, single oil is used for lubrication of bearings, control oil for
governing and hydraulic turbine turning gear. During start-ups, auxiliary oil pump (2
~ 23 ~

30. Nos.) supplies the control oil. Once the speed of the turbine crosses 90% of the rated speed,
the main oil pump takes over. Under emergency, a DC oil pump can supply lubrication oil.
Beforetheturbine is turnedorbarred,the Jacking Oil Pump (2 Nos.) supplies high pressure
oil to jack up the turbine generator shaft to prevent boundary lubrication in bearing.
The turbine is equipped with a hydraulic turning gear assembly comprising two rows of
moving blades mounted on the coupling between IP and LP rotors. The oil under pressure
supplied by the AOP strikes against the hydraulic turbine blades rotates the shaft at
110rpm (220 rpm under full vacuum condition).
Turbine shaft glands are sealed with auxiliary steam supplied by an electro-hydraulically
controlled seal steam pressure control valve. A pressure of 0.01 Kg / square-cm (g) is
maintained in the seals.
Above a load of 80 MW the turbine becomes self-sealing. The leak off steam from HPT/IPT
glands is used for sealing LPT glands.
TURBINE PROTECTION SYSTEM
Turbine protection system performs to cover the following functions:-
1. Protection of turbine from inadmissible operating conditions.
2. In case of plant failure, protection against subsequent damages.
3. It restricts occurring failures to minimum.
Standard turbine protection system comprises the
following:-hydraulic turbine protection.
The main elements of the Turbine Protection system are as follows:
1. Emergency Governors.
2. Emergency Governor Pilot Valves.
3. Emergency stop valve (ESV) Servomotors.
4. Interceptor valve (I V) Servomotors.
5. Turbine shutdown switch.
6. Electro-hydraulic transducer.
7. Initial steam pressure unloading gear.
H.P. - L.P. BY- PASS SYSTEM
The HP By-pass system in coordination with LP By-pass enables boiler operation and
loading independent of the turbine. For matching the live steam and metal temperature for
a quick start-up, by-pass stations have been provided, which dumps the steam to the
condenser through pressure reducing station and de superheaters, during the period the
steam parameters at the boiler are being raised. This allows quick rising of parameters to
a level acceptable to the turbine for rolling during start-up. It helps in quick start of turbine
and low noise level, also economizes the consumption of DM water. The HP By-pass system
consists of two parallel branches that divert steam from the Main Steam line
~ 24 ~

31. to Cold Reheaters line. The steam pressure on the valve upstream side can be maintained
at the desired level. The steam is de-superheated in order to keep the steam temperature
in cold reheat line within limits, below 345 degree Celsius. The steam downstream of the
HP by-pass station is maintained by 2 nos. pf spray water temperature control valves BPE-
1 and BPE-2 with valve mounted electro-hydraulic actuators.
With the use of turbine by-pass station it is possible to build up the matching steam
parameters at the boiler outlet during any regime of starting, independent of the steam
flow through turbine. The steam generated by boiler, and not utilized by the turbine
during start-up or shutdown, is conserved within the power cycle and thus losses of
steam into the atmosphere are cut down to the barest minimum. By-pass system enables
to shorten the start-up time.
CONDENSATE EXTRACTION PUMP (CEP)
The condensate extraction pump (CEP) is a centrifugal type vertical pump, consisting of
pump body, can, distributor housing and the driven lantern. The pump body is arranged
vertically in the can and is attached to the distributor with the rising main. The rotor is
guided in bearings lubricated by the fluid pumped, is suspended from the support bearing,
which is located in the bearing pedestal in the driven lantern. The shaft exit in the driver
lantern is sealed off by one packed stuffing box. The steam after condensing in the
condensing in the condenser known as condensate is extracted out of the condenser hot
well by condensate pump and taken to the Deaerator through ejectors, gland steam cooler
and series of LP heaters. The function of these pumps is to pump out the condensate to the
Deaerator through injector, gland steam cooler, and LP heaters. These pumps have four
stagesand since thesuction is at a negative pressure,specialarrangementshavebeenmade
for providing sealing.
BOILER FEED PUMP (BFP)
These pumps almost consume 2% of total power generation of the power plant. Basically
these pumps are meant to supply continuous water to the boiler drum.
There are two- types of BFP’s 1.
Turbine Driven (TDBFP)
2. Motor Driven (MDBFP)
Initially the plant is started with MD-BFP, and then after attaining proper steam pressure TD-BFP’s
are used to decrease power consumpti
Each BFP is provided with a Booster pump in its suction line which is driven by the main
motor of the boiler feed pump. One of the major damages which may occur to a BFP is from
Cavitation or vapour bounding at the pump suction due to suction failure. Cavitations will
occur when the suction pressure of the pump at the pump suction is equal or very near to
the vapour pressure of the liquid to be pumped at the particular feed water temperature.
By the use of the booster pump in the main pump suction line, always there will be positive
suction pressure which will remove the possibility of Cavitations. Therefore all 3 feed
pumps are provided with the main shaft driven booster pump in its suction line for
obtaining a definite positive suction pressure.
~ 25 ~

32. GENERATOR AND ITS AUXILLARIES
GENERATOR:
The 500 MW generator is a 3 -phase, horizontally mounted 2-pole cylindrical rotor type,
synchronous machine driven by steam turbine. The stator windings are cooled by de-
mineralized water flowing through the hollow conductor while the rotor winding is cooled
by hydrogen gas. Fans mounted on the generator rotor facilitate the circulation of the H2
inside the machine requiring cooling. 4 coolers mounted inside the machine cool the H2
gas. The generator winding is insulated by epoxy thermo- setting type insulation. It is
provided with static excitation system. Two H2 driers are provided to facilitate moisture
removal. H2 is circulated through them via the fans in dry condition. Normally one drier is
kept in service and other is in standby. Liquid Level Detectors (LLDs) are provided to
indicate liquid in the generator casing, to indicate whether oil is leaking or water. It can be
drained through drain valves. H2 gas purity is to be maintained at more than 99%.
The cooling water system consists of 2x100% duty AC motor driven pumps, 2x100% duty
water coolers, 2x100% duty mechanical filters, 1x100% duty magnetic filter, expansion
tank, polishing unit and ejector system. The stator water pump drive the water through
coolers, filters and winding and finally discharges into the expansion tank situated at a
height of about 5m above the TG floor. It is maintained at a vacuum of about 250mm Hg by
using water ejectors. A gas trap is provided in the system to detect any traces of hydrogen
gas leaking into the stator water system. To prevent leakage of hydrogen from generator
housing, ring type seals are provided at the both ends of the generator. The seal ring is free
to adjust its position according to shaft position.
Generator Components:
1. Rotor:
The rotor is a cast steel ingot and it is further forged and machined. The rotor is to be
designed very accurately as it has to work on speeds such as 3000 rpm. Also a fairly high
current is to be carried by the rotor windings to generate the necessary magnetic field.
2. Rotor winding:
Silver bearing copper is used for the winding with mica as the insulation between
conductors. A mechanically strong insulator such as micanite is used for lining the slots.
When rotating at high speeds centrifugal force tries to lift the windings out of the slots, so
they are screwed to the rotor body. The two ends of the windings are connected to slip
rings, usually made of forged steel.
3. Stator core:
The stator is the heaviest load to be transported. The major part of this load is stator core.
This comprises of an inner frame and outer frame. The outer frame is a rigid fabricated
structure of welded steel plates, within this shell is a fixed cage of girder built circular and
~ 26 ~

33. axial ribs. The ribs divide the yoke into compartments. The inner cage is usually fixed to
the yoke by an arrangement of springs to dampen the double frequency vibrations.
The stator core is built from a large number of punchings or sections on thin steel plates.
The use of CRGO can contribute to reduction in weight of stator core.
4. Stator windings:
Each stator conductor must be capable of carrying the rated current without overheating.
The insulation must be sufficient to prevent leakage currents flowing between the phases
to earth.
Windings for the stator are made up from copper strips wound with insulated tape which
is impregnated with varnish, driedundervacuum andhot pressedto formasolid insulation
bar.These barsarethen placedin statorslots andheld in with wedges to form thecomplete
winding. The end turns are rigidly braced and packed with blocks to withstand the heavy
forces.
Generator Cooling:-
Rotor Cooling System:
The rotor is cooled by means of gap pick up cooling, wherein the hydrogen gas in the air
gap is sucked through the scoops on the rotor wedges and is directed to flow along the
ventilating canals milled on the sides of the rotor coil, to the bottom of the slot where it
takes a turn and comes out on the similar canal milled on the other side of the rotor coil to
the hot zoneof the rotor.Dueto rotationof the rotor,a positive suction as well asdischarge
is created due to which a certain quantity of gas flows and cools the rotor.
The conductors used in the rotor windings are hollow which is done to have internal
cooling of the rotor.
Hydrogen Cooling System:
Hydrogen is used as a cooling medium due to its high heat carrying capacity and low
density. But it can also form an explosive, or escape out of the generator casing which may
result into many catastrophic results. So the pressure of H2 should be maintained properly.
The filling in and purging of H2 is to be done safely without bringing in contact with air. To
fill H2 inside generator first CO 2 is filled through generator and then H2 is passed since H2
has no reaction with CO2 and while taking H2 out of generator first H2 is taken out then CO2
is passed through generator and then air is allowed to enter.
Stator Cooling System:
The stator is cooled by distillate which is fed from one end of the machine by Teflon tube
and flows through the upper bar and returns back through the lower bar of another slot.
The stator winding is cooled in this system by circulating DM water through hollow
conductors. The DM water should be at 40°C. As it is a closed loop the water that comes out
of the generator is again cooled and de mineralized. Water passes through lower bars
~ 27 ~

34. along the length to the other end returns through the upper bars of another slot and drain
into drain header.
RATINGS OF TURBO GENERATOR
Stage-I
Rated Voltage: 15.75 kV
Rated Power: 210 MW
Rated KVA: 247 MVA
Stator Current: 9067 A
Rotor Current: 2640 A
Frequency: 50 Hz
Connection: YY (DOUBLE -STAR)
Power Factor: 0.85 LAG
Rated HB2B Pressure: 4KgF/cmP2
Operational Duty: SB1
Class of Insulation: B
Stage-II
Rated Power: 500 MVA
Rated KVA: 588MVA
Stator Voltage: 21 Kv
Stator Current: 16200A
Rotor current: 4040A
Rotor voltage: 340V
Rated H2 pressure: 3.5 bar (g)
Power factor: 0.85 lag
Stator winding cooling: Direct water cooling (DM water)
Stator core and rotor
Cooling: Direct H2 cooling
Rated Speed: 3000 rpm
Frequency: 50 Hz
Connection: YY
Class of Insulation: F
EXCITATION SYSTEM
Static excitation system

Excitation power from generator via excitation transformer. Protective relays for excitation
transformer.



Field forcing provided through 415 v aux supply



Converter divided in to no of parallel (typically4)paths. Each one having separate pulse output
stage and air flow monitoring.


Two channels : Auto & manual, provision for change over from Auto to Manual


Limiters: Stator current limiter, Rotor current limiter, Load angle limiter etc.


~ 28 ~

35.  Alternate supply for testing.
Brushless Excitation System
GT
EXC TRFR
18KV/700V
1500KVA
THYRISOR
FIELD BRIDGE
v oltage regulator
GENERATOR
400V/40V, 10KVA
Components:

 Three Phase Main Exciter. 


Three Phase Pilot Exciter. 


Regulation cubicle 


Rectifier Wheels 

 Exciter Coolers 

Metering and supervisory equipment.  
Features:

Eliminates Slip Rings,Brush gear and all problems associated with transfer of current
via sliding contacts
  Simple, Reliable and increasingly popular system the world over, Ideally suited for

large sets

Minimum operatingand maintenance cost


Self generating excitation

unaffected by system fault/disturbances because of shaft

mounted pilot exciter
~ 29 ~

36. FIELD BREAKER R
Y
ARMATURE B
ROTATING
DIODES
FIELD
(PM)
PILOT MA IN GENERAT OR
EXCITEREXCITER
3 PHASE EXCITER:
Rated power: 2135 kVA; 10.5 kW
Rated voltage: 520 V
Stator current: 2370 A
Rated Speed: 3000 RPM
Frequency: 50 Hz
Connection: YY (DOUBLE-STAR)
Self- excitation required: 65 V, 154 A
YY connection is given to reduce effective impedance of windings and to increase amount
of current output since the voltage induced remains constant.
Difference b/w Brushless Exciter and Static Exciter:
S.NO Description Brushless Excitation Static Excitation
1 Type of system. Brushless system gets activated Static excitation system uses
with pilot exciter, main thyristors & taking
exciter and rotating supply from output of
diodes. the generator
2 Dependencyon external No external source requirement Field flashing supply required
supply. since pilot exciter has for excitation build up.
permanent magnet field.
3 Response of the excitation Slower than static type since Veryfast response in the order
system. control is indirect (on the of 40 ms. due to the
field of main exciter) and direct control and solid
magnetic components state devices employed.
involved.
4 Requirement of additional
One additional bearing and an
No additional bearing and
bearing and increase of increase in shaft length
increase in the shaft
turbo generator shaft are required.
length are required.
length.
5 Maintenance. Less since slip rings and brushes More since slip rings and
are avoided. brushes are required.
Also over hang
vibrations are veryhigh
resulting in faster wear
and tear.
~ 30 ~

37. Ratings of brushless excitationsystem:
Permanent magnet generator: (pilot exciter):
Rated Power: 39kw
Rated KVA: 65kVA
Stator Voltage: 220V
Stator Current: 195A
Power factor: 0.6
Rated Speed: 3000 rpm
Frequency: 400 Hz
Connection: YYYY
Coolant: AIR
Phase: 3
Class of Insulation: F
Excitation system Details:
Stage-I Stage-II
Type Static Brushless
Excitation power 2000 kW 3780 kW
Excitation Curent 2600 A 6300 A
Excitation voltage 310 V 600 V
EXCITATION SYSTEM OF THE TURBO GENRATOR
Excitation energy for the Turbo Generator (TG)is obtained from a separate excitation
source using a thyristor exciter, which provides the controlled rectifier current to the field
winding. The thyristor (service) exciter consists of an auxiliary A.C. generator mounted on
the TG shaft and two thyristor converters cooled by distillate from the TG stator cooling
circuit.
Either of the converters is arranged in a 3-φ bridge circuit. The con in parallel and they function
simultaneously. Each converter has its own individual
thyristor firing control system, which is interconnected through the circuits for
synchronizing of firing pulses applied to the two converter arms. Due to this
interconnection, uniform sharing of load current between the parallel–operating
converters is provided and besides, each thyristor firing control system duplicates the
other if loss of supply voltage occurs.
If the service exciter fails, the TG field excitation can be provided from the standby exciter.
For this purpose, the use is made of a separately installed set consisting of a D.C. generator
and an A.C. driving motor.
The auxiliary generatoris ofthe self –excitation type. Power to the field winding is obtained
from the rectifier transformer connected to generator stator winding and the
~ 31 ~

38. thyristor converter cooled by natural air circulation. Application of the auxiliary generator
field flashing is accomplished bymeans ofshort-time connectionofa 220V separatepower
source. When applied, the separate power source provides a buildup of the generator
terminal voltage up to 10-20 % of the rated value, there upon the connected thyristor
bridgestarts to function andpromotesabuild up generatorterminal voltageup to therated
value.
Changing automatically or manually the firing angle of the thyristors in the converters
accomplishes control of the TG filed excitation. With a decrease of the auxiliary voltage to
80 % of the rated value or in the case of its complete loss, the regulator and thyristor firing
control system are supplied with back up power from a 220 V storage battery. With the
restoration of the auxiliary voltage to 84% of the rated value, the back-up power supplies
are blocked.
PROTECTIONS OF GENERATOR
The core of an electrical power system is generator. During operating conditions certain
components of the generator are subjected to increase stress and therefore, could fail,
referred to as faults. It can be internal fault or external fault depending upon whether they
are inside or outside of the machine. The machine with fault must be tripped
immediately. The corrective measures agains care by stubborn system.
Task of the protective system:
o Detect abnormal condition or defect. 
 o Limit its scope by switchingto isolate the defect. 
 o Alarm the operating staff. 
o Unload and/or trip the machine immediately.

Requirement ofprotective devices:
Selectivity:
Only that part of the installation containing fault should is disconnected.
Safety against faulty tripping: There should be no trip when there is no fault.
Reliability:
The device must act within the required time.
Sensitivity:
Lowest signal input value at which the device must act.
Tripping time:
There should be a clear a distinction between the tripping time of the device,
considering the circumstances such as current and total tripping time for the fault.
~ 32 ~

39. Protective Devices :
The choice of protective equipment for the generator should precisely understand
the type of fault and do the necessary preventive measures for avoiding it.
Electrical protection:

Differential protection:

  
Generator differential
  
UAT differential  
Overheadlinedifferential  
G.T. restrictedearth fault, Main
  
Overall differential

Earth fault protection:


Stator earth fault

 
Stator earth fault, Stand by

Rotor earth fault

 
Stator Inter turn fault
 
Negative Phase Sequence Current

Generator Backup Impedance


Loss of excitation


Pole slipping

 
Over voltage
 
Over fluxing
 
Lowforward power

Reversepower

 
Generator Local Breaker Backup (LLB)

Generator TransformerProtections


Buchholz Protection


PRD protection

 
WindingTemperature High

Oil Temperature High


Fire Protection

 
UAT Protection
 
Bus Bar Protection
As with electrical motor protection, generator protection schemes have some similarities
and overlap. This is advantageous, since not all generators have all of the protection
schemes listed in this section. In fact, there are many protection schemes available; only
the more common ones are discussed here.
Classes of Turbine Generator Trips
There are different classes of protective trips for generators, each with different actions,
depending on the cause and potential for damage. Each of the four Classes of trip (A, B, C,
&D) is discussed below.
~ 33 ~

40. Class A
trips will disconnect the generatorfromthegrid andshut downthe turbine -generator(i.e.,
it will trip the turbine and the field breaker). Typical causes could be generator electrical
protection, main transformer electrical protection, ground faults or any other cause that
may directly affect the units safe electrical output.
Class B
Trips will disconnect the generator from the grid, but will leave the turbine generator
supplying the unit load. Typical initiation of this event is a grid problem, thus resulting in
this loss of load.
Class C
Trips are generator over-excitation trips and are activated only if the generator is not
connected to the grid (it may still be supplying the unit loads). Typical causes of this over-
excitation are manually applying too much Notes: excitation or applying excitation current
below synchronous speed.
Class D
Trips the turbine and then trips the generator after motoring. The causes of this type of
trip are associated with mechanical problems with the turbine generator set. Each of these
trips, along with their causes and exact effects, will be discussed further in your station
specific training.
Generator Over-Current
As discussed in the previous sections, over-currents in the windings due to over-loads or
faults will cause extensive damage. The generator must be separated from the electrical
system and field excitation removed as quickly as possible to reduce this damage to a
minimum. During run-up and shutdown, the field may accidentally be applied while the
frequency is below 60Hz. Under these conditions normal protections may not work or may
not be sensitive enough. A sensitive over -current protection called supplementary start
over-current is usually provided when the frequency is less than about 56Hz.
1. Generator differential protection
Differential protection can be used to detect internal faults in the windings of
generators, including ground faults, short circuits and open circuits. Possible
causes of faults are damaged insulation due to aging, overheating, over-voltage,
wet insulation and mechanical damage. Examples of the application of
differential protection are shown in Figure 23 that considers a generator winding
arrangement with multiple windings, two per phase (this type of differential
protection is also called split phase protection for this reason).
~ 34 ~

41. protection is also called split phase protection for this reason).
In Figure 23 a), the currents in the two windings will be balanced, causing the currents in
the protection circuit to be balanced. Hence in this case, the differential relay will not
operate.
In Figure23 b), a groundfault is shownon oneofthe windings. In this casethe fault current
direction is shown and it will be unbalanced. This will result in unbalanced secondary
currentsin the protection circuit, causing the differential relayto operate.Similarly, ashort
circuit within a winding will cause the two winding currents to be unmatched, causing the
differential relay to operate.
In Figure 23 c), an open circuit is shown, resulting in no current in the one winding.
Again, the unbalanced currents will cause the differential relay to operate. In generators
with single windings per phase, the differential protection (Figure 24) is similar to the
transformer protection previously discussed. This arrangement will provide high -speed
Tripping of the generator and field breaker plus shutdown of the turbine (class A trip).
This minimizes insulation damage due to overheating, as well as damage from arcing if
the insulation has already been damaged.
~ 35 ~

42. 2. Generator Ground Fault Protection
Generators are usually connected to the delta winding of a delta-star main transformer.
This allows the generator to produce nearly balanced three phase currents even with
unbalanced loading on the primary of the main transformer. This minimizes stress,
vibration and heating of the stator windings during unbalanced system conditions and
electrical system faults. However, with the generator connected to a delta winding, a
separate protection has to be used to protect against stator faults. Any resistance to
ground will pull the delta towards ground and may initially go undetected by the
differential relay. The stator ground relay will trip the generator before severe damage
results. Often the groundrelayhas alow-set alarm included to allow possiblecorrection
before a trip condition exists.
3. Generator Stator Ground Protection
Figure 25 illustrates ground protection system when the generator neutral
connection is done through a neutral grounding transformer. Some locations utilize
a grounding resistor and accompanying CT. Possible causes of ground faults are
insulation damage due to aging, overheating, over-voltage, wet insulation and
mechanical damage. If the faults are not cleared, then the risk of insulation damage
will occur due to overheating (as a result of high currents) or damage from arcing if
the insulation has already been damaged.
4. Rotor Ground Fault Protection
The windings on the rotor of an AC generator produce the magnetic field at the
poles. In four pole generators (typical of 60 Hz, 1800 rpm units), the occurrence of
a single ground fault within the rotor generally has no detrimental effects. A second
ground fault, however, can have disastrous results. It can cause part of the rotor
winding to be bypassed which alters the shape of the otherwise balanced flux
pattern. Excessive vibration and even rotor/stator contact may result. A means of
detecting the first ground fault provides protection against the effects of a second
fault to ground on the rotor. Figure 26 shows a simplified excitation system with a
Ground Fault Detection (GFD) circuit. The GFD is connected to the positive side of
the exciter source.
~ 36 ~

43. 5. Generator Phase Unbalance Protection
If a generator is subjected to an unbalanced load or fault, the unbalance will show
up as ac current in the rotor field. With the 4-pole 800 rpm generators used in
nuclear stations, this current will be at twice line frequency or 120Hz. Continued
operation with a phase imbalance will cause rapid over-heating of the rotor due to
the additional induced circulating currents (these currents will also cause heating
of other internal components of the generator). This will result in rapid and uneven
heating within the generator and subsequent damage to insulation and windings
(hence, reduced machine life) and thermal distortion could occur. Also the
unbalanced magnetic forces within the generator due to these currents will cause
excessive vibration. This may result in bearing wear/damage and reduced machine
life and may result in a high vibration trip. A specialized relay to detect these
circulating currents, called a negative sequence current relay, is used to detect the
phase imbalance within the generator. The term negative sequence is just a
mathematical term to describe the effects of unbalancing a symmetrical three phase
system. The most critical phase unbalance would come from an open circuit in one
of the windings and may not be detected by any other protection. Other causes of
phase imbalance include unequal load distribution, grid faults and windings faults.
6. Generator Loss of Field Protection
When a generator develops insufficient excitation for a given load, the terminal
voltage will decrease and the generator will operate at a more leading power factor
with a largerload angle. If the loadangle becomestoo large,loss of stability andpole
slipping will occur and the turbine generator will rapidly go into over-speed with
heavy ac currents flowing in the rotor. A loss of field could be caused by an exciter
or rectifier failure, automatic voltage regulator failure, accidental tripping of the
field breaker,short circuits in the field currents,poorbrushcontact on the slip-rings
or ac power loss to the exciters (either from the station power
~ 37 ~

44. supply or from the shaft generated excitation current). A relay that sense conditions
resulting from a loss of field, such as reactive power flow to the machine, internal
impedance changes as a result of field changes or field voltage decreases, may be
used for the detection of the loss of field. A field breaker limit switch indicating that
the breaker is open also gives an indication that there is no field to the generator.
7. Generator Over-Excitation Protection
If the generator is required to produce greater than rated voltage at rated speed (or
rated voltage below rated speed), the field current must be increased above normal
(generated voltage is proportional to frequency and flux). The excess current in the
rotor and generated voltage will result in over-fluxing of the generator stator iron
and the iron cores of the main and unit service transformers. Damage due to
overheating may result in these components. Over-voltage may also cause
breakdown of insulation, resulting in faults/arcing. This problem may occur on
generators that are connected to the grid if they experience generator voltage
regulation problems. It may also occur for units during start-up or re-synchronizing
following a trip (the field breaker should open when the turbine is tripped). When
the field breaker opens, a field discharge resistor is inserted into the rotor circuit to
help prevent terminal voltage from reaching dangerous levels. Over-excitation on
start-up may be aresult ofequipment problemsorNotes:operatorerrorinapplying
excessive excitation prematurely (excitation should not be applied to the generator
until it reaches near synchronous speed). A specialized volts/hertz relay is used to
detect this condition and will trip the generator if excessive volts/hertz conditions
are detected.
8. Generator Under-frequency Protection
While connectedto astable grid,the grid frequencyandvoltageareusually constant.
If the system frequency drops excessively, it indicates that there has been a
significant increase in load. This could end to a serious problem in the grid and it is
of little use to supply a grid that may be about to collapse. In this case, the generator
would be separated from the grid. The grid (or at least portions of it) may well
collapse. The system can slowly rebuild (with system generators ready to restore
power) to proper, pre-collapse operating conditions. As mentioned above, if a
generatorconnectedto the grid hassufficient excitation applied below synchronous
speed (since grid frequency has dropped) for it to produce rated voltage, the
excitation level is actually higher than that required at synchronous speed. Over
excitation and the problems described above may result. A specialized volts/hertz
relay compares voltage level and frequency and will trip the generator if present
volts/hertz levels are exceeded.
~ 38 ~

45. 9. Generator Out of Step Protection
This protects the generator from continuing operation when the generator is pole
slipping. Pole slipping will result in mechanical rotational impacts to the turbine, as the
generator slips in and out of synchronism. This can be the result of running in an under
excited condition (see the section on loss of field) or a grid fault that has not cleared.
Relays that detect changes in impedance of the generator can be used to detect the
impedance changes that will occur when the unit slips poles. Another method to provide
this protection is to detect the loss of excitation, using the loss of field protection and
trip the unit if excitation is too low (i.e., trip the generator when pole slipping is
imminent). This has been discussed in the loss of field section of this module.
10.Generator Reverse Power Protection
Motoring refers to the process of an AC generator becoming a synchronous motor, that
is, the device changing from a producer of electrical power to a consumer of it.
Following a reactor trip or setback/step back to a very low power level, it is beneficial to
enter the motoring mode of turbine-generator operation. However, this is not a desirable
mode of operation for standby or emergency generators. They are not designed to
operate in this manner and can be seriously damaged if power is allowed to flow in
the wrong direction. A means of indicating when the transition from exporter to importer of
power occurs is provided by a device known as a reverse power relay. As its name suggests,
it is triggered by power flowing in a direction opposite to that which is normally desired.
This can be used for generator protection, as is the case with standby generators or as a
permissive alarm/interlock for turbine-generator motoring. Figure 27 shows
a typical arrangement of a reverse power protection circuit employing both a CT and a
Voltage Transformer (VT) to power the relay and hence, protect the generator. The relay
will operate when any negative power flow is detected.
~ 39 ~

46. SWITCHGEAR
INTRODUCTION
Switchgear is one that makes or breaks the electrical circuit. It is a switching device that
opens& closes a circuit that defined as apparatus used for switching, Lon rolling & protecting
the electrical circuit & equipments. The switchgear equipment is essentially concerned with
switching & interrupting currents either under normal or abnormal operating conditions. The
tubular switch with ordinary fuse is simplest form of switchgear & is used to control & protect
& other equipments in homes, offices etc. For circuits of higher ratings, a High Rupturing
Capacity (H.R.C) fuse in condition with a switch may serve the purpose of controlling &
protecting the circuit. However such switchgear cannot be used profitably on high voltage
system (3.3 KV) for 2 reasons. Firstly, when a fuse blows, it takes some time to replace it
&consequently there is interruption of service to customer. Secondly, the fuse cannot
successfully interrupt large currents that result from the High Voltage System. In order to
interrupt heavy fault currents, automatic circuit breakers are used. There are very few types
of circuit breakers in B.P.T.S they are VCB, OCB, and SF6 gas circuit breaker. The most
expensive circuit breaker is the SF6 type due to gas. There are various companies which
manufacture these circuit breakers: ABB, L&T, ALSTOM. Switchgear includes switches, fuses,
circuit breakers, relays & other equipments.
THE EQUIPMENTS THAT NORMALLY FALL IN THIS CATEGORY ARE:-
1. ISOLATOR
An isolator is one that can break the electrical circuit when the circuit is to be switched on
no load. These are used in various circuits for isolating the certain portion when required
for maintenance etc. An operating mechanism box normally installed at ground level drives
the isolator. The box has an operating mechanism in addition to its contactor circuit and
auxiliary contacts may be solenoid operated pneumatic three phase motor or DC motor
transmitting through a spur gear to the torsion shaft of the isolator. Certain interlocks are
also provided with the isolator
These are
1. Isolator cannot operate unless breaker is open
2. Bus 1 and bus 2 isolators cannot be closed simultaneously
3. The interlock can be bypass in the event of closing of bus coupler breaker.
4. No isolator can operate when the corresponding earth switch is on
~ 40 ~

47. 2. SWITCHING ISOLATOR
Switching isolator is capable of:
1. Interrupting charging current
2. Interrupting transformer magnetizing current
3. Load transformer switching. Its main application is in connection with
the transformer feeder as the unit makes it possible to switch gear one
transformer while the other is still on load.
3. CIRCUIT BREAKER
One which can make or break the circuit on load and even on faults is referred to as circuit
breakers. This equipment is the most important and is heavy duty equipment mainly utilized
for protection of various circuits and operations on load. Normally circuit breakers installed
are accompanied by isolators.
4. LOAD BREAK SWITCHES
These are those interrupting devices which can make or break circuits. These are normally
on same circuit, which are backed by circuit breakers
5. EARTH SWITCHES
Devices which are used normally to earth a particular system, to avoid any accident
happening due to induction on account of live adjoining circuits. These equipments do not
handle any appreciable current at all. Apart from this equipment there are a number
of relays etc. which are used in switchgear.

LT SWITCHGEAR

In LT switchgear there is no interlocking. It is classified in following ways:-

1. MAIN SWITCH
Main switch is control equipment which controls or disconnects the main supply. The main switch
for 3 phase supply is available for the range 32A, 63A, 100A, 200Q, 300A at 500V grade.
~ 41 ~

48. 2. FUSES
With Avery high generating capacity of the modern power stations extremely heavy carnets
would flow in the fault and the fuse clearing the fault would be required to withstand
extremely heavy stress in process. It is used for supplying power to auxiliaries with backup
fuse protection. With fuses, quick break, quick make and double break switch fuses for 63A and
100A, switch fuses for 200A,400A, 600A, 800A and 1000A are used.
3. CONTACTORS
AC Contractors are 3 poles suitable for D.O.L Starting of motors and protecting the connected
motors.
~ 42 ~

49. 4. OVERLOAD RELAY
For overload protection, thermal overload relay are best suited for this purpose. They operate
due to the action of heat generated by passage of current through relay element.
5. AIR CIRCUIT BREAKERS
It is seen that use of oil in circuit breaker may cause a fire. So in all circuits breakers at
large capacity air at high pressure is used which is maximum at the time of quick
tripping of contacts. This reduces the possibility of sparking. The pressure may vary from 50-
60kg/cm^2 for high and medium capacity circuit breakers.

HT SWITCHGEAR


1. MINIMUM OIL CIRCUIT BREAKER

These use oil as quenching medium. It comprises of simple dead tank row pursuing projection
from it. The moving contracts are carried on an iron arm lifted by a long insulating tension
rod and are closed simultaneously pneumatic operating mechanism by means of tensions but
throw off spring to be provided at mouth of the control the main current within the controlled
device.
~ 43 ~

50. o Type-HKH 12/1000c·
o Rated Voltage-66 KV
o Normal Current-1250A·
o Frequency-5Hz·
o Breaking Capacity-3.4+KA Symmetrical
o 3.4+KA Asymmetrical
o 360 MVA Symmetrical
o Motor Voltage-220 V/DC
o Rated Voltage-12 KV
o Supply Voltage Closing-220 V/DC

~ 44 ~

51. 2. AIR CIRCUIT BREAKER
In this the compressed air pressure around 15
kg per cm^2 is used for extinction of arc
caused by flow of air around the moving
circuit . The breaker is closed by applying
pressure at lower opening and opened by
applying pressure at upper opening. When
contacts operate, the cold air rushes around
the movable contacts and blown the arc:
It has the following advantages over OCB:-
i. Fire hazard due to oil are eliminated.
ii. Operation takes place quickly.
iii. There is less burning of contacts since the duration is short and consistent.
iv. Facility for frequent operation since the cooling medium is replaced constantly.
Rated Voltage-6.6 KV Current-630 A
Auxiliary current-220 V/DC
3. SF6 CIRCUIT BREAKER
This type of circuit breaker is of construction to
dead tank bulk oil to circuit breaker but the principle
of current interruption is similar to that of air blast
circuit breaker. It simply employs the arc
extinguishing medium namely SF6. When it is
broken down under an electrical stress, it will
quickly reconstitute itself.
~ 45 ~

52. 






Circuit Breakers-HPA
Standard-1 EC 56
Rated Voltage-12 KV
Insulation Level-28/75 KV
Rated Frequency-50 Hz
Breaking Current-40 KA
Rated Current-1600 A
Making Capacity-110 KA
4. VACUUM CIRCUIT BREAKER
It works on the principle that vacuum is used to save the purpose of insulation and. In regards of
insulation and strength, vacuum is superior dielectric medium and is better that all other
medium except air and sulphur which are generally used at high pressure.




Rated frequency-50 Hz·
Rated making Current-10 Peak
KA Rated Voltage-12 KV
Supply Voltage Closing-220 V/DC
~ 46 ~

53. SWITCHYARD
Switchyard is considered as the HEART of the Power Plant. Power generated can be
worthful only if it is successfully transmitted and received by its consumers. Switchyard
plays a very important role as a buffer between the generation and transmission. It is a
junction, which carries the generated power to its destination (i.e. consumers). Switchyard
is basically a yard or an open area where many different kinds of equipments are located
(isolator, circuit breaker etc…), responsible for connect transmission line as per requirement
(e.g. any fault condition).
Power transmission is done at a higher voltage.
(Higher transmission voltage reduces transmission losses). Therefore, the power generated
by the Turbo generator of 1 to 6 units is 15.75KV and of 6 to 12 units is 21KV which is
further stepped-up to 400KV by the Generating transformer & then transmitted to
switchyard.
Switchyards can be of400KV &132KV.
In VSTPS there are two interconnected switchyards:-
(i) 400KV SWITCHYARD
(ii) 132KV SWITCHYARD
400KV SWITCHYARD:
There are on total 21 bays in this switchyard.
(A bay is basically a way for the incoming power from generator as well as
outgoing power for distribution).
7 for unit Generating Transformer.
7 for various distribution lines such as:
satna line;
jabalpur #1 line;
korba line;
~ 47 ~

54. jabalpur #2 line;
Rihand #1 line;
SSTPP line;
Rihand #2 line;
2 for Bus
coupler. 2 for
TBC.
2 for ICT.
1 for the Bus Section.
There are on total 6 buses in 400KV switchyard. There are two
transfer buses: Transfer bus-1
Transfer bus-2
Transfer buses are kept spare and remain idle and are used only for emergency purposes.
BUS COUPLER-1 & BUS COUPLER-2 interconnects Bus-1 & Bus-2, Bus-3 & Bus-4
respectively. Bus couplers are very beneficial as they help in load sharing between the
different buses.
132KV SWITCHYARD:
There are 15 bays in 132KV switchyard.


4 for Station Transformer. 
 
4 for C.W. Transformer.
 for Colony Transformer. 

for I.C.T. 
 1 for S-V-R line. 

1 for Bus Coupler.  
There are only 2 buses in 132KV switchyard.
Bus-1 is arranged in U-shape configuration
Whereas Bus-2 is a single straight line inserted in between U-shaped Bus-
1. BUS COUPLER is used to couple Bus-1 & Bus-2.
C.W.Transformer Bay:
There are 4 C.W.Transformer connected with 132 KV
switchyard. (C.W. #1, C.W. #2, C.W. #3, C.W. #4) rated at 25 MVA.
The main purpose of C.W. Transformer is to step-down the system voltage of 132 KV to
6.9 KV, which is required for C.W. Pump Motor used for condensing the water.
Colony Transformer Bay:
There are 2 Colony Transformer connected with 132KV switchyard.
(Colony Transformer#1 & Colony Transformer#2) rated at 12.5 MVA.
The purpose of Colony Transformer is to step- down the system voltage of 132 KV to
11 KV for supplying the electricity to colonies for domestic purposes.
~ 48 ~

56. SWITCHYARD EQUIPMENTS
1. Lightening arrestor
2. Current transformer
3. Voltage transformer (CVT)
4. Power transformers / I.C.T.
5. Bus bar and clamp fittings
6. Support structure
7. Isolators
8. Circuit Breaker
9. Wave traps
10. Earthing switch
~ 49 ~

57. STAGE: 4, ONE AND HALF BREAKERSCHEME
~ 50 ~

58. ISOLATORS
• Operates under no load condition
• Interlocked with breakers and earth switches
• Should withstand extreme wind pressures
• Motor driven and hand driven
• Local as well as remote operation possible
• Isolates sections for maintenance
• Used to select bus bars
• CT switching for bus bar protection
400KV HORIZONTAL CENTRAL BREAK TYPE ISOLATOR
EARTH SWITCHES
• USED TO GROUND SECTIONS REQUIRED FOR MAINTENANCE
• GROUND INDUCTION VOLTAGES
• INTERLOCKED WITH BREAKERS AND ISOLATORS
• CAN OPERATE FROM LOCAL ONLY
• MOTOR DRIVEN AS WELL AS HAND DRIVEN & SAFETY DEVICE
~ 51 ~

59. CURRENT TRANSFORMER
• Current Transformer is an instrument transformer which transforms current
from one level to another level, such as, 1000A/1A (CT ratio) i.e. transforms
current from the level of 1000A into current of 1A level
• Direct measurement of high current (in the tune of 100A or more) is not possible
as devices used for measurement of current are not designed to handle such huge
amount of current
Why Current Transformer is required
• System has two basic requirements
  
meteringof energy sourced or consumed
  
Protection of the electrical system from faults and disturbances
• Types of Current Transformer (CT)
• Measuring CTs
• Protection CTs
• Protection CTs for special applications
Where Current Transformer is connected:
• For metering and protection of a feeder, CT is connected at the beginning of the
feeder
• It has a primary winding and one or more secondary windings wound on core of
magnetic material
• Metering and Protection devices are connected to the secondaries of the CT
~ 52~

60. CAPACITIVE VOLTAGE TRANSFORMER
Primary voltage is applied to a series of capacitors group. The voltage across one of the
capacitor is taken to aux PT. The secondary of the aux PT is taken for measurement and
protection.
 secondary voltages(110 volts ac) for meters and energy meters
• voltages for protective relays
• voltages for synchronizing
• disturbance recorders and event logs
• over flux relay
~ 53 ~

61. LIGHTENING ARRESTOR
To discharge the high voltage surges in the power system due to lightning to the ground.
Apparatus to be protected:
 
Overhead lines………Earth/Ground wires (PA=30DEG) 
 HV equipment………LAs 

Substation…………...Lightning Masts, Earth wire  
SURGE ARESSTOR
CIRCUIT BREAKER
A circuit breaker can either make or break a circuit either automatically or manually, like
no load, full load and short circuit conditions. The characteristic feature of a circuit breaker
has made it a very useful electrical device in electrical power system.
Types of circuit breakers:-
1) Oil circuit breakers
2) Air blast circuit breakers
3) Sulphur hexafluoride circuit breakers
4) Vacuum circuit breakers
Oil circuit breakers:
As the name suggests, the principle arc quenching medium in this case is oil. Whenever the
fixed contacts are separated from the moving contacts, an arc is struck in between the
contacts, which cannot be allowed in a circuit. The same needs to be extinguished.
Therefore, as soon as the arc is struck, the arcing medium is completely surrounded by oil,
and the heat of the arc, thus produced helps in producing hydrogen gas, which helps in
quenching the arc.
Advantages of oil circuit breaker:
~ 54 ~

62. 1) The hydrogen gas thus produced has excellent cooling properties. Hence it cools
the arc.
2) The volume of hydrogen gas is about 1000 times, that of air. Thus it causes
turbulence in the arcing region, thus eliminating the arcing products.
Disadvantages of oil circuit breakers:
The oil circuit breakers also have a few limitations. They are:
1) The use of oil as the arc quenching medium increases the risk of fire.
2) Reuse of the oil leads to carbonisation and degradation of the oil.
Air blast circuit breakers:
The air blast circuit breakers are another category of circuit breakers which use air as the
arc quenching medium. They, in a similar manner, remove the arcing products from the
arcing region, thus extinguishing the arc.
Advantages of air blast circuit breakers:
1) The risk of fire, as in the oil circuit breakers is removed.
2) The problem of carbonisation is also r degrade its quality.
Disadvantages of air blast circuit breakers:
1) Air blast circuit breakers have inferior arc quenching properties.
2) Regular maintenance of the compressor plant is required, which supplies the air
blast.
Sulphur hexa-fluoride (SF6 ) circuit breakers:
The Sulphur hexafluoride circuit breakers are the most widely used circuit breakers.
They involve the use of sulphur hexafluoride gas, which acts as an arc quenching medium.
Advantages of the sulphur hexafluoride circuit breakers:
1) Due to their superior arc quenching properties, they have very low arcing time.
2) Since the dielectric strengthofthe gasis veryhigh, they can interrupthigh values
of current.
Disadvantages of sulphur hexafluoride circuit breakers:
1) Sulphur hexafluoride gas is expensive.
2) Regular conditioning of the gas is required, especially after use.
~ 55 ~

63. PROTECTION OF SWITCHYARD
Line Protection:
For EHV lines distance protection are used as Main protection. The measurement principle
of the protection is based on measuring the impedance of the lines from the point of relay
to the fault. This impedance is proportional to the distance. The relay can be set by
calculating the impedance of the total length of the line based on the available data of line
i.e. resistance and reactance / Km and length of line.
The relay always measures the impedance of the line when the line voltage & current are
connected to the relay. The measured values are compared with the setting. In case of fault
on the line the impedance measured shall be less than the set value & fall in the operating
characteristic of the relay & the relay will operate to trip the respective breaker. The
resistance and reactance of the line are independently set on the relay i.e. the characteristic
shall be trapezoidal.
Local Breaker Back up Protection:
All the protections of the Generator transformer and unit auxiliary transformers finally
operate the Generator master trip relay. This master trip relay issues tripping command to
Generator bay breaker. In the event, the Generator breaker does not open within preset
time say 200 ms, the LBB scheme is energized.
Generator Feeder Protection
Bus-Bar Protection
Reactor Protection
ESSENTIAL QUALITIES OF ELECTRICAL PROTECTION
Having looked at the fundamental purpose of electrical protection, we should cover the
four main building blocks that are used to meet these requirements:
Speed
When electrical faults or short circuits occur, the damage produced is largely dependent
upon the time the fault persists. Therefore, it is desirable that electrical faults be
interrupted as quickly as possible. Since 1965, great strides have been made in this area.
High-speed fault detecting relays can now operate in as little time as 10 milliseconds and
~ 56 ~

64. output relaying in 2 milliseconds. The use of protection zones, that will be discussed later,
minimized the requirement for time-delayed relaying.
Reliability & Security
The protective system must function whenever it is called upon to operate, since the
consequencesofnon-operationcanbeverysevere.This is accomplishedby duplicate A and
B protections and duplicate power supplies. Protections must isolate only the faulted
equipment, with no over-tripping ofunaffectedequipment. This is accomplishedby the use
of over-lapping protection zones.
Sensitivity
The protection must be able to distinguish between healthy and fault conditions, i.e., to
detect, operate and initiate tripping before a fault reaches a dangerous condition. On the
otherhand, the protection must not be too sensitive andoperateunnecessarily. Some loads
take large inrush starting currents, which must be accommodated to prevent unnecessary
tripping while still tripping for fault conditions. The ability of relaying to fulfil the
sensitivity requirement is improved through the use of protection zones. The basic idea
behind the use of protection zones is that every component in an electrical system (i.e., bus,
transformer, motor, and generator) hasdistinct characteristics. Protections can be made to
perform faster (speed), with increased security and increased sensitivity if it deals with
only that one element. As we start to look at the electrical system in view of protection
zones, we have to get a clear picture of where the boundaries of these zones will normally
be in any electrical system. For simple systems such as a motor in the diagram below, the
fuse or thermal circuit breaker would be the boundary of the zone. The ratings of the fuse
would be designed to protect that motor only.
HVDC Backto backSystem
A back-to-back station (or B2B for short) is a plant in which both converters are in
the same area, usually in the same building. The length of the direct current line is kept
as short as possible. HVDC back-to-back stations are used for
 coupling of electricity grids of different frequencies (as Northern and western grid) 

 coupling two networks of the same nominal frequency but no fixed phase relationship
(as until 1995/96 in Etzenricht, Dürnrohr,Vienna, and the Vyborg HVDC scheme). 

 different frequency and phase number (for example, as a replacement for traction
current converter plants) 
The DC voltage in the intermediate circuit can be selected freely at HVDC back-to-back
stations because of the short conductor length. The DC voltage is usually selected to be as
low as possible, in order to build a small valve hall and to reduce the number of thyristors
connected in series in each valve. For this reason, at HVDC back-to-back stations, valves
with the highest available current rating (in some cases, up to 4,500 A) used.
~ 57 ~

65.  VINDHYACHAL HVDC: 
Data sheet of Vindhyachal HVDC are:
1. Date of completion: April 1989
2. Specification:
a) Power rating: 2 x 250 MW
b) No. of blocks: 2
c) AC voltage: 400KV
d) DC voltage: ±70KV
e) Converter transformer: 8 x 156 KVA
System Salient Features:
1. It connects Vindhyachal Super Thermal Power Stations (Western Region) to
Singrauli Super Thermal Power Stations (Northern Region) in Indian Grid.
2. Each Block power carrying capacity is 250 MW.
3. Bidirectional power flow capability is available.
4. The project achieve load diversity of Northern and Western region in Indian Grid
by meeting high demand from surplus power available in either regions.
5. First commercial Back to Back HVDC Station in India
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66. Water Treatment Plant and Storage
Since there is continuous withdrawal of steam and continuous return of condensate
to the boiler, losses due to blow down and leakages have to be made up to maintain a
desired water level in the boiler steam drum. For this, continuous make-up water is added
to the boiler water system. Impurities in the raw water input to the plant generally consist
ofcalcium andmagnesium salts which impart hardnessto thewater. Hardnessin the make-
up water to the boiler will form deposits on the tube water surfaces which will lead to
overheating and failure of the tubes.
Thus, the salts have to be removed from the water, and that is done by a water de-
mineralizing treatment plant (DM). A DM plant generally consists of cation, anion, and
mixed bed exchangers. Any ions in the final water from this process consist essentially of
hydrogen ions and hydroxide ions, which recombine to form pure water. Very pure DM
water becomeshighly corrosiveonceit absorbsoxygenfromthe atmospherebecauseofits
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. The piping and valves are generally of stainless.
CONCLUSION
Industrial training being an integral part of engineering curriculum provides not
only easier understanding but also helps acquaint an individual with technologies. It
exposes an individual to practical aspect of all things which differ considerably from
theoretical models. During my training, I gained a lot of practical knowledge which
otherwise could have been exclusive to me. The practical exposure required here will pay
rich dividends to me when I will set my foot as an Engineer.
The training at NTPC Vindhyachal was altogether an exotic experience, since work,
culture and mutual cooperation was excellent here. Moreover fruitful result of adherence
to quality controlawarenessofsafety andemployees werefarewhich is muchevident here.
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67. BIBLIOGRAPHY
 WIKIPEDIA  
 PRESENTATIONS FROM EDC DEPARTMENT,VSTPP  
 PRESENTATION FROM SENIORS AND EMPLOYEES OF VSTPP  
 NTPC VSTPP WEBSITE  
 SLIDESHARE 
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