Download - thermal power plant bathinda
-
8/10/2019 thermal power plant bathinda
1/58
-
8/10/2019 thermal power plant bathinda
2/58
INTRODUCTION
Guru Nanak Dev Thermal Power Plant is a coal-based plant. The requirement of coal for four units based
on specific fuel consumption of 0.60 kg / kWh. The conveying and crushing system will have the same
capacity as that of the unloading system. The coal comes in as large pieces. This coal is fed to primary
crushers, which reduce the size of coal pieces from 400mm to 150mm. Then the coal is sent to secondary
crusher through forward conveyors where it is crushed from 150mm to 200mm as required at the mills.
Then the coal is sent to boilers with the help of primary fans. The coal is burnt in the boiler. Boiler includes
the pipes carrying water through them; heat produced from the combustion of coal is used to convert
water in pipes into steam. This steam generated is used to run the turbine. When turbine rotates, the
shaft of generator, which is mechanically coupled to the shaft of turbine, gets rotated so, three phase
electric supply is produced.
The basic requirements are:-
Fuel (coal)
Boiler
Steam turbine
Generator
Ash handling system
Unit auxiliaries
-
8/10/2019 thermal power plant bathinda
3/58
BRIEF HISTORY OF THERMAL PLANT
Due to high rate of increasing population day by day, widening gap between power demand and its
availability was one the basic reason for envisaging the G.N.D.T.P. for the state of Punjab. The
other factors favoring the installation of the thermal power station were low initial cost and
comparatively less gestation period as compared to hydro electric generating stations. The
foundation stone of G.N.D.T.P. at Bathinda was laid on 19th
November 1969, the auspicious
occasion of 500th
birth anniversary of great Guru Nanak Dev Ji.
The historic town of Bathinda was selected for this first and prestigious thermal project of
the state due to its good railway connections for fast transportations of coal, availability of canal
water and proximity to load center.
The total installed capacity of the power station 440MW with four units of 110MW each. The
first unit of the plant was commissioned in September, 1974. Subsequently second, third and
fourth units started generation in September 1975, March 1978, and January 1979 respectively.
The power available from this plant gives spin to the wheels of industry and agricultural pumping
sets.
-
8/10/2019 thermal power plant bathinda
4/58
R&M WORKS AT GNDTP, BATHINDA
R&M of GNDTP unit 1&2 has already been completed pending PG Test. R&M works of unit 3&4
is underway to improve performance, enhance capacity and extend operating life of the units. The
present status of R&M works of GNDTP units is as under:
Unit I&II: - Against approved project Report of Rs. 229 Crores, Order was placed on M/S NASL,
New Delhi for major R&M works on Turnkey basis at a total of Rs.183 Crores.
Unit II: R&M works completed in October, 2005 (Pending attending to some deficiencies by the
firm). Average PLF achieved post R&M works is 87%.
Unit I: - R&M works completed and taken for normal operation in May, 2007(Pending attending
to some deficiencies by the firm). Average PLF achieved post R&M during May07 and June 07
is 95.65%.
Unit III & IV: - Order for executing R&M works on Turnkey basis already placed on M/S BHEL
at a total cost of Rs. 465.36 Crores. 10% advance payment has been made to M/S BHEL on
22/12/2006 and design and drawing work is in progress. As per Schedule, work is to be completed
in a phased manner upto July 2009. Apart from enhancing the operating life and performance level
of the units, it is also planned to upgrade the capacity from 110 MW to 120 MW each resulting in
total capacity addition of 20 MW.
-
8/10/2019 thermal power plant bathinda
5/58
SITE SELECTION
The selection of site for Thermal Power Plant is more difficult compared to Hydro Power Plant,
as it involves number of factors to be considered for its economic justification. The following
consideration should be examined in detail before selection of the site for the Plant. The location
for plant should be made with full consideration not only of the trends in the development and
location but also the availability and location of the cheapest source of primary energy:-
Availability of fuel
Ash disposal facilities
Space requirement
Nature of land
Availability of labour
Transport facilities
Public society problems
Development of Backward Area
-
8/10/2019 thermal power plant bathinda
6/58
LANDMARK ACHIEVED
G.N.D.T.P. won an award of Rs. 3.16 crores from Govt. of India for better performance
in 1983-84.
It achieved a rare distinction of scoring hart Rick by winning meritorious productivity
awards of Govt. of India, Ministry of Energy for year 1987, 1988 and 1989 due to its better
performance.
It again won meritorious productivity awards during the year 1992-1993 and 1993-94 and
has become entitled for the year 1996-1997 for better performance.
It also won awards for reduction in fuel oil consumption under Govt. of India incentive
scheme years from 1992-1993 (awards money for 1992, 1993 and 1994 already released
for 1995, 1996 and 1997 under the consideration of Govt. of India).
G.N.D.T.P. had achieved a generation of 2724240 LUs (at a PLf of 70%) and registe ring an
oil consumption as low as 1.76ml/kwh during the year 1993-94 has broken all previous
records of performance since the inception of plant.
-
8/10/2019 thermal power plant bathinda
7/58
CONTRIBUTION OF THE PLANT
Guru Nanak Dev Thermal Plant, Bathinda, in addition to indirect contribution in various facts of
state economy, is also responsible for:-
Narrowing the gap between power demand and power availability of the state.
Providing employment potentials to thousands of workers.
Covering the backward surrounding area into fully developed Industrial Township.
Providing additional relief to agricultural pumping sets to meet the irrigation needs for
enhancing the agriculture production.
Reliability and improvement in continuity of supply and system voltage.
Achieving cent percent rural electrification of the state.
-
8/10/2019 thermal power plant bathinda
8/58
PLANT SALIENT FEATURES
PROJECT AREA:
POWER PLANT 238 ACRES
ASH DISPOSAL 845
LAKE 180
RESIDENYIAL COLONY 285
MARSHALLING YARD 256
TOTAL AREA 1804
TOTAL COST Rs 115 CRORES
STATION CAPACITY FOUR UNITS OF 120 MW EACH
BOILER:-
MANUFACTURERS B.H.E.L.
MAXIMUM CONTINOUS RATING(M.C.R).
375T/hr
SUPERHEATER OUTLET PRESSURE 139 kg/cm
REHEATER OUTLET PRESSURE 33.8 kg/cm
FINAL SUPERHEATER/REHEATERPRESSURE
540C
FEED WATER TEMPERATURE 240C
EFFICIENCY 86%
COAL CONSUMPYION PER DAY PERUNIT
1400 tones (approximate)
-
8/10/2019 thermal power plant bathinda
9/58
STEAM TURBINE:-
MANUFACTURERS B.H.E.L.
RATED OUTPUT 11O MW
RATED SPEED 3000 rpm
NUMBER OF CYLINDERS 3
RATED PRESSURE 130 kg/cm
RATED TEMPERATURE 535C
CONDENSER VACUUM 0.9 kg/cm
GENERATOR:-
MANUFACTURERS B.H.E.L.
RATED OUTPUT
UNIT 1 & 2UNIT 3 & 4
125000 KVA137000 KVA
GENERATOR VOLTAGE 11000 voltage
RATED PHASE CURRENT
UNIT 1 & 2UNIT 3 & 4
6560 A7220 A
GENERATOR COOLING HYDROGEN
BOILER FEED PUMPS:-
-
8/10/2019 thermal power plant bathinda
10/58
NUMBER PER UNIT TWO OF 100% DUTY EACH
TYPE CENTRIFUGAL
RATED DISCHARGE 445 T/hr
DISCHARGE HEAD 1960 MWC.
SPEED 4500 RPM
CIRCULATING WATER PUMPS:-
NUMBERS FOR TWO UNITS FIVE OF 50% DUTY EACH
TYPE MIXED FLOW
RATED DISCHARGE 8600T/hr
DISCHARGE HEAD 24 MWC
COOLING TOWERS:-
-
8/10/2019 thermal power plant bathinda
11/58
NUMBERS FOUR
WATER COOLED 18000T/hr
COOLING RANGE 10C
HEIGHT 120/12 m
COAL PULVERISING MILLS:-
NUMBERS THREE PER UNIT
TYPE DRUM BALL
RATED OUTPUT 27 T/hr
COAL BUNKERS 16 PER UNIT
-
8/10/2019 thermal power plant bathinda
12/58
RATING OF 6.6 KV AUXILLIARY MOTORS:-
COAL MILL 630 KW
VAPOUR FAN 320 KW
C.W. FAN 800/746 KW
COAL CRUSHER 520 KW
PRIMARY AIR FAN 320 KW
FORCED DROUGHT FAN 320 KW
BOILER FEED PUMP 3500 KW
INDUCED DROUGHT FAN 900/1000 KW
CONDENSATE PUMP 175 KW
-
8/10/2019 thermal power plant bathinda
13/58
WORKING OF THERMAL PLANT
Coal received from collieries in the rail wagon is mechanically unloaded by Wagon Tippler
and carried by belt Conveyor System Boiler Raw Coal Bunkers after crushing in the coal crusher.
The crushed coal when not required for Raw Coal Bunker is carried to the coal storage area
through belt conveyor. The raw coal feeder regulates the quantity of coal from coal bunker to the
coal mill, where the coal is pulverized to a fine powder. The pulverized coal is then sucked by the
vapour fan and finally stored in pulverized coal bunkers. The pulverized coal is then pushed to
boiler furnace with the help of hot air steam supplied by primary air fan. The coal being in
pulverized state gets burnt immediately in the boiler furnace, which is comprised of water tube
wall all around through which water circulates. The water gets converted into steam by heat
released by the combustion of fuel in the furnace. The air required for the combustion if coal is
supplied by forced draught fan. This air is however heated by the outgoing flue gases in the air
heaters before entering the furnace.
The products of combustion in the furnace are the flue gases and the ash. About 20% of the
ash falls in the bottom ash hopper of the boiler and is periodically removed mechanically. The
remaining ash carried by the flue gases, is separated in the electrostatic precipitators and further
disposed off in the ash damping area. The cleaner flue gases are let off to atmosphere through the
chimney by induced draught fan.
The chemically treated water running through the water walls of boiler furnace gets
evaporated at high temperature into steam by absorption of furnace heat. The steam is further
heated in the super heater. The dry steam at high temperature is then led to the turbine comprising
of three cylinders. The thermal energy of this steam is utilized in turbine for rotating its shaft at
high speed. The steam discharged from high pressure (H.P.) turbine is returned to boiler reheaterfor heating it once again before passing it into the medium pressure (M.P.) turbine. The steam is
then let to the coupled to turbine shaft is the rotor of the generator, which produces electricity. The
power from the generator is pumped into power grid system through the generator transformer by
stepping up the voltage.
-
8/10/2019 thermal power plant bathinda
14/58
-
8/10/2019 thermal power plant bathinda
15/58
The steam after doing the useful work in turbine is condensed to water in the condenser for
recycling in the boiler. The water is pumped to deaerator from the condenser by the condensate
extraction pumps after being heated in the low pressure heater (L.P.H) from the deaerator, a hot
water storage tank. The boiler feed pump discharge feed water to boiler at the economizer by the
hot flue gases leaving the boiler, before entering the boiler drum to which the water walls and
super heater of boiler are connected.
The condenser is having a large number of brass tubes through which the cold water is
circulated continuously for condensing the steam passing out sides the surface of the brass tubes,
which has discharged down by circulating it through the cooling tower shell. The natural draught
of cold air is created in the cooling tower, cools the water fall in the sump and is then recirculated
by circulating water pumps to the condenser.
-
8/10/2019 thermal power plant bathinda
16/58
GENERAL DESCRIPTION
BOILER FEED PUMP:-
As the heart is to human body, so is the boiler feed pump to the steam power plant. It is used for
recycling feed water into the boiler at a high pressure for reconversion into steam. Two nos. 100%
duty, barrel design, horizontal, centrifugal multistage feed pumps with hydraulic coupling are
provided for each unit. This is the largest auxiliary of the power plant driven by 3500 KW electric
motor. The capacity of each boiler at GURU NANAK DEV THERMAL PLANT is 375
tones/hr. The pump which supplies feed water to the boiler is named as boiler feed pump. This is
the largest auxiliary in the unit with 100% capacity which takes suction of feed water from feed
water tank and supplies to the boiler drum after preheating the same in HP-1, HP-2 and
economizer. The delivery capacity of each boiler feed pump is 445 tones/hr. to meet better
requirements corresponding to the various loads, to control steam temperature, boiler make up
water etc. The detailed particulars checking of protections and inter locks, starting permission etc.
are as below:-
Particulars of BFP and its main motor:-
BOILER FEED PUMP: -The 110 MW turboset is provided with two boiler feed pumps,
each of 100% of total quantity. It is of barrel design and is of horizontal arrangement,
driven by an electric motor through a hydraulic coupling.
Type 200 KHI
No. of stages 6
Delivery capacity 445 t/hr.
Feed water temperature 158C
Speed 4500 rpm
Pressure at suction 8.30 kg/cm
-
8/10/2019 thermal power plant bathinda
17/58
Stuffing box mechanical seal
Lubrication of pump by oil under pressure
And motor bearing supplied by hydraulic coupling
Consumption of cooling water 230 L/min.
WATER TREATMENT PLANT:-
The water before it can be used in the boiler has to be chemically treated, since untreated water
results in scale formation in the boiler tubes especially at high pressure and temperatures. The
water is demineralised by Ion Exchange Process. The water treatment plant has production
capacity of 1800 Tonnes per day for meeting the make-up water requirement of the power station.
COAL MI LL :-
Coal Mill pulverizes the raw coal into a fine powder before it is burnt in the boiler furnace. The
pulverizing of coal is achieved with the impact of falling steel balls, weighing 52.5 tonnes,
contained in the mill drum rotating at a slow speed of 17.5 r.p.m. The raw coal is dried, before
pulverizing, with inert hot flue gases tapped from the boiler. Three coal mills each with a
pulverizing capacity of 27 T/hr. are provided for one unit.
INDUCED DRAUGHT FAN:-
Two nos. axial flow Induced Draught Fans are provided for each unit to exhaust ash laden flue
gases from boiler furnace through dust extraction equipment and to chimney. The fan is driven by
an electric motor through a flexible coupling and is equipped with remote controlled regulating
vanes to balance draught conditions in the furnace. The fan is designed to handle hot flue gases
with a small percentage of abrasive particles in suspension.
CONTROL ROOM:-
The control room is the operational nerve center of the power plant. The performance of all the
equipments of the plant is constantly monitored here with the help of sophisticated instrumentation
and controllers. Any adverse deviation in the parameters of various systems is immediately
-
8/10/2019 thermal power plant bathinda
18/58
indicated by visual and audio warning and suitable corrective action is taken, accordingly. The
control room is air conditioned to maintain the desired temperature for proper functioning of the
instruments.
SWITCH YARD:-
Electricity generated at 11 KV by the turbo-set is stepped-up by unit transformers to 132/220 KV
for further transmission through high tension lines to Maur, Muktsar, Malout, N.F.L., Sangrur and
Ludhiana. Transmission of power to grid is controlled through 7 nos. 220 KV and 15 nos. 132 KV.
Air Blast Circuit Breakers along with their associated protective systems.
WAGON TIPPLER:-
The coal received from the collieries, in more than 100 rail wagons a day, is unloaded
mechanically by two nos. wagon tipplers out of which one serves as a standby. Each loaded wagon
is emptied by tippling it in the underground coal hopper from where the coal is carried by
conveyor to the crusher house. Arrangements have been provided for weighing each rail wagon
before and after tippling. Each tippler is capable of unloading 6-8 rail wagons of 55 tonnes
capacity in an hour.
CRUSHER HOUSE:-
Coal unloaded by the wagon tippler is carried to crusher house through conveyors for crushing.
Two nos. hammer type coal crushers are provided, which can crush coal to a size of 10 mm. The
crushed coal is then supplied to Boiler Raw Coal Bunkers. The surplus coal is carried to coal
storage area by series of conveyors. Crushing of coal is an essential requirement for its optimum
pulverizing and safe storage.
COOLING TOWERS:-
Cooling Towers of the power plant are the land mark of the Bathinda City even for a far distance
of 8-10 kilometers. One cooling tower is provided for each unit for cooling 18000 tones of water
per hour by 10C. cooling towers are massive Ferro-concrete structure having hyperbolic profile
creating natural draught of air responsible for achieving the cooling effect. Cooling tower is as
high as 40 storey building.
-
8/10/2019 thermal power plant bathinda
19/58
BOILER:-
It is a single drum, balanced draught, natural circulation, reheat type, vertical combustion chamber
consists of seamless steel tubes on all its sides through which water circulates and is converted into
steam with the combustion of fuel. The temperature inside the furnace where the fuel is burnt is of
the order of 1500C. The entire boiler structure is of 42meter height.
BOILER CHIMNEY:-
The flue from the boiler, after removal of ash in the precipitators, are let off to atmosphere through
boiler chimney, a tall ferro-concrete structure standing as high as the historic Qutab Minar. Four
chimneys, one for each unit, are installed. The chimney is lined with fire bricks for protection of
ferro-concrete against hot flue gases. A protective coating of acid resistant paint is applied outside
on its top 10 meters.
CIRCULATI NG WATER PUMP:-
Two nos. of circulating water pumps provided for each unit, circulate water at the rate of 17200
T/hr. in a closed cycle comprising of Turbine Condenser and Cooling Tower. An additional
Circulating Water Pump provided serves by for two units. The water requirement for bearing
cooling of all the plant auxiliaries is also catered by these pumps.
-
8/10/2019 thermal power plant bathinda
20/58
COAL HANDLING PLANT (CHP)
The G.N.D.T.P. units are primarily coal-fired units and the coal consumption at maximum
continuous rating (M.C.R.) per unit is about 58 T/Hr. the coal used at G.N.D.T.P. is of bituminous
and sub-bituminous type and this is received from some collieries of M.P. and Bihar. The designed
composition of coal is as below:-
1. Type Bituminous Coal
2. Net calorific value 4300 kcal/kg
3. Moisture content in coal 10%
4. Ash content 30%
5. Volatile matter in combustibles 24%
6. Grind ability index 50 Hard Groove
The coal handling plant at G.N.D.T.P. has been supplied and erected by M/s Elecon
Engineering Company Limited, Vallabh Vidya Nagar, Gujarat. Coal is transported from the coal
mines to the plant site by Railways. Generally, the raw coal comes by railway wagons of either
eight wheels weighing about 75 to 80 tones each or four wheels weighing about 35 to 40 tones
each. The loaded wagon rake is brought by railways main line loco and left on one of the loaded
wagon tracks in the power station marshalling yard. The main line loco escapes through the engine
track. The station marshalling yard is provided with 8 tracks. The arrangement of the tracks in the
marshalling yard is as follows:-
-
8/10/2019 thermal power plant bathinda
21/58
DESTINATION NO. OF TRACKS
Loaded wagons receiving tracks Four
Empty wagon standing tracks Three
Engine escape tracks One
UNLOADING OF COAL:-
In order to unload coal from the wagons, two Roadside Tipplers of Elecon make are
provided. Each is capable of unloading 12 open type of wagons per hour. Normally one tippler
will be in operation while the other will be standby. The loaded wagons are brought to the tippler
side by the loco shunters. Then with the help of inhaul beetle one wagon is brought on the tippler
table. The wagon is then tilted upside down and emptied in the hopper down below. The emptied
wagon comes back to the tippler table and the outhaul beetle handles the empty wagons on the
discharge side of the tippler. The tippler is equipped with the integral weighbridge machine. This
machine consists of a set of weighing levers centrally disposed relative to tippler. The rail platform
rests on the weighing girders and free from rest of the tippler when the wagon is being weighed.
After weighing the loaded wagons is tipped and returned empty to the weighing girders and again
weighed. Thus the difference of the gross weight and the tare weight gives the weight of the
wagon contents. The tipplers are run by motors of 80 H.P. each through gears only.
WAGON TIPPLER
-
8/10/2019 thermal power plant bathinda
22/58
The tippler is designed to work on the following cycle of operation:-
Tipping 90 seconds
Pause 5-12 seconds
Return 90 seconds
Weighing 30 seconds
Total 215-222 seconds
Allowing 85 seconds for wagon changing it will be seen that 12 eight-wheel wagons or
24 four-wheel wagons per hours can be tipped. However since the coal carrying capacity is 500
tones per hour load of 12 wagons comes to 8 to 9 per hour.
When coal reaches the plant, normal size of coal is about 500mmprimary
crusher120mmsecondary crusher25mmcoal millpulvarised coal, feeded in boiler.
IMPROVED DESIGN OF WAGON TIPPLER:-
We under the new scheme, propose to raise the level of hopper to the ground
level. Correspondingly, the level of the platform of wagon tippler will also have to be adjusted.
Also the building structure covering the hopper and tripper will be done away with keeping the
hopper open. In this way the screen of the hopper becomes accessible to pay loader trucks. Now,
when the screen gets blocked, a pay loader truck can be employed which will lift all the over sized
coal and take it to a suitable place where it can be broken either manually or by a crusher. Thus it
will save time as the trolleys can be emptied faster, saving damages.
DUST TRAPPING SYSTEM:-
The tippler is also provided with the dust trapping systems by which the dust nuisance
will be minimized. As the tippler rotates, a normally closed hopper valve opens automatically and
the discharged material passes through it into the hopper with its dust-setting chamber, there is an
air valve of large area, which opens, simultaneously with the hopper valve. The object of this air
-
8/10/2019 thermal power plant bathinda
23/58
valve is to blow back through the hopper valve into the tipping chamber, which must occur if, the
settling chamber were closed, it being remembered that a large wagon contains some 240 cubic
feet of material and that this volume of dust air would be forced back at each tip if the hopper
chamber were a closed bottle. The air valve and the hopper valve are shut immediately on
reversal of the tippler and are kept shut at all times except during the actual discharge. The hopper
valve is operated by a motor of 10 H.P., 415 Volts and the air valve is operated by electro-
hydraulic thruster. Inlet valve consists of large number of plates sliding under the wagon tippler
grating. Coal in the wagon tippler hopper forms the heap and as such obstructs the movement of
sliding valve and damaging the plates. The inlet and outlet valves have therefore been bypassed.
The unloaded material falls into the wagon tippler hopper (common to both tipplers)
having a capacity of 210 tones. The hopper has been provided with a grating of 300mm X 300mm
size at the top so as to large size boulders getting into the coal stream. There is also a provision of
unloading the wagons manually into the MANUALLY UNLOADED HOPPER of 110 tones
capacity. Manually unloading will be restored to while unloading coal from sick wagons or closed
wagons.
CONVEYING SYSTEM
A belt conveyor consists of two or more pulleys, with a continuous loop of material - the
conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt
and the material on the belt forward. The powered pulley is called the drive pulley while the
unpowered pulley is called the idler. There are two main industrial classes of belt conveyors;
Those in general material handling such as those moving boxes along inside a factory and bulk
material handling such as those used to transport industrial and agricultural materials, such as
grain, coal, ores, etc. generally in outdoor locations. Generally companies providing general
material handling type belt conveyors do not provide the conveyors for bulk material handling. In
addition there are a number of commercial applications of belt conveyors such as those ingrocery
stores.The belt consists of one or more layers of material they can be made out of rubber. Many
belts in general material handling have two layers. An under layer of material to provide linear
strength and shape called a carcass and an over layer called the cover. The carcass is often a cotton
http://en.wikipedia.org/wiki/Pulleyhttp://en.wikipedia.org/wiki/Bulk_material_handlinghttp://en.wikipedia.org/wiki/Bulk_material_handlinghttp://en.wikipedia.org/wiki/Grocery_storehttp://en.wikipedia.org/wiki/Grocery_storehttp://en.wikipedia.org/wiki/Grocery_storehttp://en.wikipedia.org/wiki/Grocery_storehttp://en.wikipedia.org/wiki/Bulk_material_handlinghttp://en.wikipedia.org/wiki/Bulk_material_handlinghttp://en.wikipedia.org/wiki/Pulley -
8/10/2019 thermal power plant bathinda
24/58
or plastic web or mesh. The cover is often various rubber or plastic compounds specified by use of
the belt. Covers can be made from more exotic materials for unusual applications such as silicone
for heat or gum rubber when traction is essential.
CONVEYING SYSTEM
MAGNETIC PULLEYS:-
On belt conveyor no. 4A and 4B, there have been provided high intensity electromagnetic
pulleys for separating out tramp iron particles/pieces from the main stream of coal conveying.
D.C. supply for the magnet is taken on 415 volt, 3 phase, 50 cycles A.C. supply system.
In addition to above high intensity suspension type electromagnets have also been provided
on belt conveyors 4A and 4B for separating out tramp iron pieces/particles.
-
8/10/2019 thermal power plant bathinda
25/58
RECLAIMING:-
If the receipt of coal on any day more than the requirement of the boilers, the balanced
material will be stocked via conveyor 7Aand 7B and through telescopic chute fitted at the end of
the conveyor. At the end of the chute one tele level switch is provided, which automatically lifts
the telescopic chute to a predetermined height every time. The tele level switch is actuated by the
coal pile. When the telescopic chute reaches maximum height during operation, which will be cut
off by limit, switch and stop the conveying system. When the pile under the telescopic chute is
cleared, the telescopic chute can be independently lower manually by push buttons.
There are five bulldozers to spread and compact the coal pile. Bulldozers of Bharat Earth
Movers Limited Make are fitted with 250 H.P. diesel engines. Each bulldozer is able to spread the
crushed coal at the rate of 250 tones/hr. over a load distance of 60m the coal can be stacked to a
height of 6m the stockpile stores coal for about 45 days for four units with an annual load factor of
0.66.
Whenever coal is to be reclaimed the bulldozers are employed to push the coal in the
reclaim hopper having a capacity of 110 tones. The coal from the reclaim hopper is fed either 9A
or 9B belt conveyor through vibratory feeders 8A and 8B.
CRUSHER HOUSE:-
The crusher house accommodates the discharge ends of the conveyor 4A, 4B
receiving ends of conveyor 5A, 5B and conveyor 7A and 7B, two crushers, vibrating feeders and
necessary chute work. There are two crushers each driven by 700H.P. electric motor, 3 phase, 50
cycles and 6.6 kV supply. The maximum size of the crushed coal is 10mm. The capacity of each
crusher is 500 tones/hr. one crusher works at a time and the other is standby. From the crusher the
coal can be fed either to the conveyors 5A, 5B or 7A, 7B by adjusting the flap provided for this
purpose. There is built in arrangement of bypassing the crusher by which the coal can be fed
directly to the conveyors bypassing crusher.
-
8/10/2019 thermal power plant bathinda
26/58
CRUSHER HOUSE
Coal unloaded by the wagon tippler is carried to crusher house through conveyors for crushing.
Two nos. hammer type coal crushers are provided which can crush coal to a size of 10 mm. The
crushed coal is then supplied to boiler Raw Coal Bunkers. The surplus cursed coal is carried to
coal storage area by series of conveyors. Crushing of coal is an essential requirement for its
optimum pulverizing and safe storage.
-
8/10/2019 thermal power plant bathinda
27/58
BITUMINOUS COAL:-
Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called
bitumen. It is of higher quality than lignite coal but of poorer quality than ANTHRACITE.
Formation is usually the result of high pressure being exerted on lignite. Its coloration can be black
or sometimes dark brown; often there are well defined bands of bright and dull material within theseams. These distinctive sequences which are classified according to either dull, bright-banded
or bright, dull-banded, is how bituminous coal are stratigraphically identified.
Bituminous coal is an organic sedimentary rock formed by diagenetic and sub
metamorphic compression of peat bog material. Its primary constituents are macerals: vitrinite and
liptinite. The carbon content of bituminous coal is around 60-80%; the rest is composed of water,
air, hydrogen and sulphur, which have not been driven off from macerals.
SPECIFICATIONS:-
BANK DENSITY 1346 kg/m3
BULK DENSITY 833kg/m3
HEAT CONTENT 24-35MJ/kg (21 million to 30 million BTU per
short ton)
BITUMINOUS COAL
-
8/10/2019 thermal power plant bathinda
28/58
BOILER SECTION
BOILER SECTION:- The steam generating unit is designed to meet the nominal requirements
of 110MW turbo generator set. The unit is designed for a maximum continuous rating of 375
tones/hr. at a pressure of 139kg/cm2 and a steam temperature of 5400C. the reheated steam flows
at MCR 32H tones/hr. at the feed water temp at MCR is 2400C. The unit is a balance draught dry
bottom; single drum natural circulation, vertical water tube type, construction with skin casing and
a single reheat system. The furnace is arranged for dry ash discharge and is fitted with burners
located at the four corners. Each corner burner comprises coal, vapour oil and secondary air
compartments. The unit is provided with three ball mills and arranged to operate with intermediate
cool powder bunker. The steam super heater consists of 4 stages Viz. Ceiling, convection, platen
and final superheated. The ceiling super heated forms the roof of the furnace and horizontal pass
-
8/10/2019 thermal power plant bathinda
29/58
and finishes as the rear wall of the second pass. The convection super heated is made up of
horizontal banks located in the second pass. While the platens are located at the furnace exit, the
portion above the furnace nose encloses the final superheated reheater are in two stages, first stage
is the triflux heat exchangers located in the second pass, which absorbs heat from superheated
steam as well as from the flue gases. The second stage is exit reheater located in the horizontal
pass as pendant tubular loops.
(a) The flue gas for drying the cool in the mills is tapped off after the triflux heat exchangers. The
damper located in the hot flue gases pipe leading to mill controls the quantity. Control the
circulating vapour of the mill entry effect temperature control.
Immediately after the triflux heat exchanger, the air heaters and economizers are located. The air
heater is in 2 stages.
(b) The hot air for combustion from air heater stage 2 is led into the common wind box located on
the sided of the furnace. 4 cool air mixed pipes from pulverized coal bounders are connected to 4
cool burners nozzle at the corners. There will be totally 16 coal nozzles. 4 located in each corner.
Oil guns will be located in the secondary air nozzle for coal burning. The turn down ratio of the
guns will be so selected that it will be possible to use them also for pulverized fuels flame
stabilization while operating under load below the control point.
(c) Take into consideration the high % age of ash and the relatively poor quality of coal due
regards has been paid to wide pitching the tubes and to the gas velocity across the heating surface
areas. In order to insure reliable and continuous operation sample sot blowing equipment is
provided. There are short retractable steam root blowers provide at the top of furnace fully
retractable rotary type blowers are located for cleaning of the secondary super heater and final
heater partly retractable steam blowers are arranged for the horizontal reheater and super heaters in
the second pass. The steam root blowers are electrically operated.
(d) Root blowing nozzles using blow down from boilers drum are provide for the cleaning of areas
around the burners nozzles zone for dislodging of slag boulder if any in the bottom ash hopper in
the furnace.
(e) Two FD fans are provided per boiler. The FD fans are of the axial type driven by constant
speed motor. The regulation of quantity and pressure is done by inlet vane control. The flue gases
-
8/10/2019 thermal power plant bathinda
30/58
are sucked through the mechanical and electrostatic precipitators by I.D. fans and delivered into
the chimney. Two I.D. fans are provided for each boiler and they are of the axial type driven by
constant speed motors. Inlet vane control effects the capacity change with reference to load. Both
the I.D. and FD fans have been dimensioned taking into account the minimum margins of 15% on
volume and 32% on pressure.
BOILER
-
8/10/2019 thermal power plant bathinda
31/58
Specification
Manufacturer B.H.E.L
Maximum continuous rating 375tones/hr.
Super heater outlet pressure 139kg /cm2
Reheater outlet pressure 33.8 kg/cm2
Final super heater temperature 540 deg.c
Feed water temperature 240deg.c
Efficiency 86% (stage-1)
87% (stage-2)
Coal consumption per day 1500 tones
Outdoor/indoor boiler Outdoor boiler Water tube/fire tube boiler Water tube Boiler
Forced draught/balanced draught Balanced draught boiler
Direct coal fired/indirect coal fired Indirect coal fired
Dry bottom/wet bottom boiler Dry bottom boiler
Single drum boiler/multi drum boiler Single drum boiler
Natural circulation/forced circulation Natural circulation
-
8/10/2019 thermal power plant bathinda
32/58
TURBINE SECTION
The steam rotates the turbine blades at a high speed of 3,000 rpm. This turns the power generator,
which is directly connected to the turbines, and electricity is produced as a result. This electric
power is then delivered along power transmission lines and through substations to the homes of
customers.
Turbine is a prime mover for the Generator in the power plant. In steam
turbine, the potential energy of steam is transformed into kinetic energy and later in its turn is
transformed into the mechanical energy of the rotation of the turbine shaft. The common types of
turbines are:-
IMPULSE TURBINE: - In this type of turbine, steam expands in the nozzles and its pressure
does not alter as it moves over the blades.
REACTION TURBINE: - In this type of turbine, the steam expands continuously as it passes
over the blades and thus there is a gradual fall in pressure during expansion.
Different types of steam turbines are used in Thermal Power Plant but the ones which
are used at G.N.D.T.P. are categorized as follows:-
Sr. No. TYPE OF TURBINE TURBINES AT G.N.D.T.P.
1. HORIZONTAL/VERTICAL HORIZONTAL
2. SINGLE/MULTI CYLINDER MULTI-CYLINDER
3. IMPULSE/REACTION IMPULSE
4. CONDENSING/NON-
CONDENSING
CONDENSING
5. REHEAT/NON-REHEAT REHEAT
6. REGENERATIVE/NON-
REGENERATIVE
7. WITH BYPASS/ WITHOUT
BYPASS
WITH BYPASS (ST-1)
WITHOUT BYPASS (ST-2)
-
8/10/2019 thermal power plant bathinda
33/58
TURBINE SPECIFICATIONS:-
MANUFACTURERS B.H.E.L.
RATED OUTPUT 11O MW
RATED SPEED 3000 rpm
NUMBER OF CYLINDERS 3
RATED PRESSURE 130 kg/cm
RATED TEMPERATURE 535C
CONDENSER VACUUM 0.9 kg/cm
BASIC WORKING OF TURBINE
First of all the turbine is run on gear motor with the help of exciter. At that time steam is kept on
recirculating with the help of by pass valve. When the pressure of steam is increased to on
optimum level and turbine acquires a particular rpm then steam is introduced in the H.P. (high-
pressure) cylinder first. The temperature of steam at entrance is 540C and pressure is about 139
Kg/cm2. After doing its work on the H.P. Turbine, the steam is taken out for reheating rated
temperature of steam at reheater inlet is 360C. The temperature of steam is increased upto 535C
in the boiler shell and steam is again introduced in M.P (Medium pressure) turbine. After
M.P.turbine, the steam is passed on to L.P. (Low-pressure) turbine. This process helps the turbine
to reach the speed of 3000 rpm. After L.P. turbine, the steam is condensed in condenser, build
below the turbine unit. The condenser contains a number of brass tubes through which cooling out
from L.P. turbine it comes in contact with colder brass tubes then steam get transformed into
water. This water get collected in HOT WELL just below the condenser. From here the hot water
is again pumped with the help of condensate pumps. The cooling water is used to condense steam
gets heated up and is cooled by falling from cooling tower. This completes the processing of steam
through turbine and condenser.
-
8/10/2019 thermal power plant bathinda
34/58
ROTOR OF TURBINE
All the rotors are manually by means of rigid coupling, including the rotors of the generator. The
speed of whole system of rotor lies in the following ranges of the speed at the operating
conditions: -
1900 to 2000 rpm Bestnoticed on the M.P. and L.P. rotors and generators.
2350 rpm Bestnoticed on H.P. rotor.
1. BEARING OF ROTORS
The axial load of the entire system of rotors is taken up by a double-sided axial bearing located in
the bearing stand between the H.P. and M.P casing. These are two protections mounted near the
axial bearing one hydro chemical and one electromagnetic, which fouls the turboset during the
non-permissible movement of the rotor.
The rotors are placed on radial bearing which are machined to elliptical shape. Further scrapping
operations or change top and side clearances and change in temperature of oil, influence the oil
wedge and the position of the journal bearing to maintain the same condition as existed during the
initial assembly.
In the lower half of bearing a hollow groove is provided in the babbit metal through which oil the
supplied through a drilled hole through H.P. jacking oil pumps.
The high-pressure oil rotors are lifted in the bearing so that any scrapping of the bearing is
prevented.
2. TURBINE CASING
The high-pressure part of turbine is consisted of two-concentric horizontal casing. Inner casing is
connected in such a way to the other casing that it enables to expand in all direction. The nozzles
are attached to the inner casing. The steam pipe is connected to the condensers and the condensers
-
8/10/2019 thermal power plant bathinda
35/58
are supported by springs. The casings are inter connected by the system of guide keys through
bearing pedestals in such a way that thermal expansion of casing does not destroy the various parts
of turbine.
The displacement-bearing pedestal between M.P. and H.P parts is measured by the
electromagnetic pick up. This valve is about of 15 mm to prevent deformation at the casing. It is
very important that sliding part clean lubricated and free from hazard for connecting parts bolts
elements. The heating of bolts before tightening up and before the locking presents. The flanges of
M.P. and H.P. casings are designed to heat up by steam during the starting up of turbo boost by
which the difference in temperature between the cylindrical position of the casing flanges and
connected bolts is reduced to limited deformation. The thermo couples are used for measuring
temperatures. The thermo couple is partially connected to the indicated apparatus. Cooling fluid is
generally used for reducing the temperature of various parts.
3. REGULATION AND SAFETY EQUIPMENT FOR TURBINE GOVERNING
The quality of steam entering in the turbine is regulated by the four governing
valves on the inlet to the M.P. part. The amount of opening at any instant of these valves is
controlled by the pressure of secondary oil, which is indirectly depending on the primary oil
pressure and directly depending upon the spring force in the transformer during the stand still and
during starting of the turbo set. The pressure of primary oil is directly depending on the speed of
the set through the speed-sensing element. Operating the speed changer or the normal speed
changer can very the tension in the spring in the transformer.
-
8/10/2019 thermal power plant bathinda
36/58
Thus make it possible to vary the speed before synchronizing. In case break down of any
equipment of the block the quick closing devices are provided in the regulation system of the turbo
set. H.P. quick closing valves (H.P.Q.C) M.P. quick closing valves (M.P.Q.C) at return flap valves
are operated by either directly by the tripling lever or through the relay magnet on the main relay
which creates instantaneously loss of pressure of the quick closing oil by the change of flow of oil
inside the relay.
Distribution is used for checking the function of H.P.Q.C and M.P.Q.C valves.
The H.P. and M.P quick closing valves, the non return flaps and non return extraction valves
during normal operating condition have only two positions one is fully opened another fully
closed.
-
8/10/2019 thermal power plant bathinda
37/58
4. STEAM CYCLE
The design of the power cycle based on the modern concept, where a unit consists of a steam
generator with its independent firing system tied to the steam generation. The steam generator is
designed for maximum continuous rating of 375-tonnes/hr. and steam Pressure of 139-kg/cm2at
temperature of 540C respectively. The steam generator is designed to supply to a single reheat
type condensing steam turbine with a 8 non regulated extraction points of steam for heading the
condensate and feed water. The steam cycle can be classified into the following three divisions: -
(a) Main steam
(b) Reheat steam
(c) extraction steam
(a) MAIN STEAM
Saturated steam from the steam generator drum is led to the super heater bank to heat if up to
540C saturated steam from the drum is led to the ceiling super heater (between SHH1 and SHH2)
from ceiling super steam goes to convection.
Super heater (between SHH2 and SHH3) the first regulated infection for at
temperature takes place after convection super heater (between SHH9 and SHH10). Before entry
to final super heater the steam is again at temperature by regulated injection. The steam is coming
out from the final super heater normally at a pressure of 139 kg/cm2at a temperature of 540
oC.
This steam is feed to the control valve. In each of the two live steam lines there is one turbine side
main steam stop valve and one high pressure quick closing valve along with two control valves .
(b)EXTRACTION STEAM
Steam for heating of the condenser and the feed steam is extracted from 8 non regulated extraction
points from the turbine. Heating is carried out in five stages of L.P. heaters, one deareating heater
and in two H.P. heaters extraction 1, 2, 3, is taken from L.P. turbine. Extraction 4, 5, 6 and 7 are
taken from M.P. turbine. Extraction 8 is obtained from C.R.H. line first and second stage of
heating is done by two sets of twin low-pressure heaters mounted directly in the L.P. casing of the
-
8/10/2019 thermal power plant bathinda
38/58
turbine. Extraction 3, 4 and 5 are connected to the deaereating heater placed above feed water
storage tank 7th
and 8th
extraction steam is fed to the vertical H.P. heaters respectively.
(C)REHEAT STEAM
Exit steam from the H.P. turbine is taken back to the reheater section of the steam generating unit.
Reheating is done in two stages both by flue gas and by super heated steam. The steam to be
reheated is first pass through the triple-heated exchanger, where super heated steam is used as the
heating media. The steam is finally reheated in final reheaters (RHH3) RHH4 and RHH5)
suspended in the horizontal pass of the furnace. Reheat steam at a normal pressure of 36.4 kg/cm2
at a temperature of 540C respectively is fed to the M.P. cylinder by two hot reheat steam pipes
through strainers and combined stop and interceptor valves. In each of the cold reheat steam linesfrom H.P. cylinder a non-return valve is operated by oil pressure is provided.
5. Turbine Accessories and Auxiliaries
a. Surface condenser.
b. Steam jet air ejector
c. LP and HP heaters.
d.
Chimney steam condenser.
e. Gland steam condenser.
f. Oil purifier or centrifuge.
g. Clean oil pump with clean oil tank
h. Dirty oil pump with clean oil tank.
i. Auxiliary oil pump with auxiliary oil tank
j. Starting oil pump.
k.
Emergency oil pump.
(I) SURFACE CONDENSER
-
8/10/2019 thermal power plant bathinda
39/58
Two surface condensers are used for condensing the steam which has worked in the turbine. The
coolant for condensing the steam is circulating water which is inside the condenser brass tubes and
steam is outside.
Technical data of Condenser
Cooling Area 3300 msq.
Number of brass tubes 6000
Circulating water required 7500 tonnes/hr.
Vacuum in the condenser 0.90 kg/cm sq.
(II) STEAM JET AI R EJECTOR
Starting ejector is used for quick evacuation of the turbo set during starting whereas main steam jet
air ejector is used to maintain Vacuum in the condenser. It works on the principle of VENTURI
with steam working media to eject air from the condenser.
(III) LP AND HP HEATERS
In regenerative system there is a steam of 5 LP heaters, one Deaereator, 2 HP heaters. All LP and
HP heaters are of surface type i.e. condensate or feed water is inside the heater tubes in the heater
shells. L.P. heaters are of single flow whereas HP heaters are of double flow type. Deaereator is
contact type heater in which steam and condensate come in direct contact.
(IV, V) CHIMNEY STEAM AND GLAND STEAM CODENSER: -
There are additional two heating stages provided in the regeneration system of the turbine for
heating the condense flowing through it steam leaks off from the turbine glands is used for heating
the condensate in these heaters.
(VI, VII, VIII, IX, X)VARIOUS OIL PUMPS
Centrifuge is an oil purifier used to remove moisture and other impurities from the turbine oil.
Maximum allowable moisture content in the turbine oil is 0.2%. In case the oil level of the main
-
8/10/2019 thermal power plant bathinda
40/58
oil tank is to be made up then either oil can transferred from clean oil tank to main oil tank with
centrifuge or from dirty oil tank to main oil tank with centrifuge.
(XI) STARTING OIL PUMPS AND EMERGENCY OIL PUMPSStarting oil pumps supply the necessary turbine oil during starting of the turbine and upto turbine
speed of 2930 rpm till the main oil pump mounted on the turbine rotor at the HP extension takes
manually in order to provide lubrication oil for the turbo set. Emergency oil pumps are meant to
start on auto, when turbine trips and lubrication oil pressure falls in order to provide lubrication to
the turbine and generator bearings.
MAIN TECHNI CAL DATA ABOUT TURBINE
a) The Basic Parameters
Rated output measured at terminal of the generator. 110,000KW
Economical output. 95,000KW
Rated speed 3,000 RPM
Rated temp. Of steam just before the stop valve. 535C
Max temp. Of steam before the stop valve 545C
Rated pressure of steam before the MP casing 31.63 atm
Max. Pressure of steam before the MP casing 35 atm
Rated temp. Of steam before the MP casing 535C
Max. Temp. of steam before the MP casing 545C
-
8/10/2019 thermal power plant bathinda
41/58
b) System of turbine:
Governing valves 2 interceptor valves
HP cylinder 2 rows Curtis wheels +8 moving wheels
Wt. HP rotor approx. 55000 kg
MP cylinder 12 moving wheels
Wt. of MP rotor approx. 11000 kg
LP cylinder 4 moving wheels with double flow design
Wt. of LP cylinder 24000 kg
RELAY SECTION
Protective relay is a device that detects the fault and initiates the operation of the circuit breaker to
isolate the defective section from the rest of the system.
We have seen that whenever fault occurs on the power system, the relay detects
the fault and closes the trip coil circuit. This results in the opening of circuit breaker, which
disconnects the faulty section. Thus a relay ensures the safety of the circuit equipments from
damage which may be causes by the faulty current.
ESSENTIAL ELEMENTS OF A RELAY
All the relays have the following three essential fundamental elements as shown in block diagram
see fig.
(a) Sensing element: - Sensing or measuring element is the element which responds to the change
in magnitude or phase of the actuating quantity e.g. current in the over current relay.
(b) Comparing element: - It is the element which compares the action of the actuation quantity of
the relay with pre-designed relay setting. The relays only pick up if the actuating quantity is more
than the relay setting.
-
8/10/2019 thermal power plant bathinda
42/58
(c) Control Element: -When a relay picks up it accomplishes a sudden change in the controlled
quantity such as closing of trip coil circuit.
1. TYPES OF RELAYS
There are many kinds of relays applied in the power system. The relays can be designed and
constructed. To, operate in response to one or more electrical quantities such as voltage, current,
phase angle etc. The relays are classified in different ways.
According to construction and principle of operation
(i) Thermal relays: - The heating effect of electric current is used for the operation of these
relays.
(ii) Electromagnetic attraction relays: - The operation of these relays depends upon the
movement of an armature under the influence of attractive forces due to the magnetic field set up
by current flowing through the relay coil.
(iii) Induction Relays: - Electromagnetic induction phenomenon is used for the operation of
these relays by induction, eddy currents are induced in the aluminum disc, free to rotate, which
exerts torque on it.
2.ACCORDING TO APPLI CATION
i) Over current, over voltage or over power relays:-These relays operate when the current,
voltage or power rises beyond a specific value.
ii) Directional or reverse current relays: - These relays operate when the applied current
assumes a specified phase displacement with respect to the applied voltage and the relay is
compensated for fall in voltage.
iii)Under current, under voltage or under power relays: - These relays operated when the
current, voltage or power falls below a specific value.
iv)Directional or reverse power relays: - These relays operate when the applied voltage and
current assumes a specified phase. Displacement and no compensation is allowed for fall in
voltage.
-
8/10/2019 thermal power plant bathinda
43/58
v) Distance relays: - The operation of these relays depends upon the ratio of the voltage to
the current.
vi)Differential relays: - The operation of these relays takes place at some specific phase
difference or magnitude difference between two or more electrical quantities.
3. ACCORDING TO THE TYPE OF OPERATION
(i) Instantaneous relays:-In these relays, complete operation takes place instantaneously i.e.,
the operation is complete in a negligibly small interval of time from the incidence of the actuating
quantity.
(ii) Definite time lag Relays: - In these relays operation takes place after definite time lag
which is independent of the magnitude of actuating quantity.
(iii) Inverse time lag Relays:In these relays the time of operation is inversely proportional to
the magnitude of actuating quantity.
Inverse Definite Minimum Time Lag Relays: - In these relays, the time of operation is
approximately inversely proportional to the actuating quantity, but is never less than a definite
minimum time for which relay is set.
THERMAL RELAYS
A relay in which heating effect of electric current is used for its operation is known as thermal
relays. These relays may be actuated by A.C or D.C.
CONSTRUCTION
The schematic diagram of an indirectly heated general purpose thermal relay is shown in fig. It hasa bimetallic strip which is heated by heating element which gets supply from a current transformer.
An insulated contact arm carrying a moving contact is pivoted and is held by a spring. The other
contact of trip circuit is a fixed contact. The spring tension can be varied by changing the position
of contact arm with the help of sector plate.
-
8/10/2019 thermal power plant bathinda
44/58
WORKING
Under normal conditions, the current flowing through the heating element is
proportional to the normal full load current of the circuit. The heat produced by the heating
element, under this condition is not sufficient to bend the bimetallic strip. However, when fault
occurs current flowing through the heating element increases which produces heat sufficient to
bend the bimetallic strip. This releases the contact arm and because of the spring tension the relays
contacts are closed which closes the trip coil circuit or the alarm circuit once the alarm circuit or
the trip coil circuit is closed; it operates the alarm circuit or the circuit breaker to open the circuit
respectively.
These over current tripping relays are use mostly for motor controls. The heating
elements of such relays are designed to with stand short time overload up to 7 times the normal
full load.
ELECTROMAGNETIC ATTRACTION RELAYS
Electromagnetic attraction type relays are operated by virtue of an armature being attracted
towards the poles of an electromagnet. These relays may be actuated by D.C. or A.C. quantities.
-
8/10/2019 thermal power plant bathinda
45/58
Construction
The schematic diagram of an electromagnetic attraction type relay is shown in fig. It consists of a
magnet which carries a relay coil having number of tapings. The armature is held by the spring
attached it. The armature has spring loaded moving contact which bridges the trip coil circuit.
Working
Under normal conditions, the current flowing through the relay coil is such that spring tension is
more than the attractive force of the electromagnet. Therefore armature is held in the open
position. However when fault occurs, current flowing through the relay coil increases. This
increases the attractive force of the electromagnet. At the instant when attractive force of
electromagnet is more than the spring tension, the armature is tilted down wards and moving
contact bridges the fixed contacts. This closes the trip coil circuit.
The current setting can be adjusted by changing the number of turn of relay coil. The
larger numbers of turns are introduced in the operating coil, the smaller is the value of actuating
current. The time setting can adjust by changing the tension of spring by a screw. Terminal AC act
as normally can also be used for the operation of another circuit.
-
8/10/2019 thermal power plant bathinda
46/58
INDUCTION RELAYS
The basic principle of operation of these relays is electromagnetic induction. These relays are only
actuated by a.c. An induction relay essentially consists of a pivoted aluminum disc place inbetween two alternating fields of the same frequency but displaced from each other by some angle.
A torque is produced in the disc by the interaction of two fields. Such relays may be over current
reverse power or directional over current relays as discussed in the coming articles.
INDUCTION TYPE OVER CURENT RELAY
Construction
An induction type over current relay is shown in fig. 5 (a) it consists of an aluminum disc which is
free to rotate to be placed in between the two electromagnets. The upper magnet has three limbs
whereas lower magnet has two. The tapped winding is wound on the central limbs of the upper
magnet. This winding is connected to the CT of the line to be protected. The tapings one
connected to a plug setting bridge as shown in fig.5 (a) by changing the position of plug by which
the number of active turns of the primary winding can be varried, thereby the desired current
setting is obtained. The secondary is a closed winding and wound on the central limb of the upper
magnet and both the limbs of the lower magnet. The winding is energized by the primary winding.
The controlling torque is provided by connected a spiral spring on the spindle of the disc. The
spindle of the disc also carries a moving contact, when the disc rotated through a preset angle, the
moving contact bridges the two fixed contact of the trip coil circuit as shown in fig.5 (b). The
preset angle can be adjusted to any value between Oand 360, by adjusting the angle, the travel
of the moving contact can be adjusted and the relay can be set for any desired time setting.
Working
When current flows through the primary winding, an E.M.F. is induced in the secondary winding
by induction. Since secondary is closed, a current flows through it. The fluxes are produced by the
currents flows through primary and secondary winding. These fluxes are separated in phase and
space and produces a driving torque on the disc. This torque is opposed by the restraining torque
-
8/10/2019 thermal power plant bathinda
47/58
provided by the spring. Under normal conditions, the restraining torque is more than the driving
torque; therefore, the disc remains stationary.
However when a fault occurs, the current flowing through the primary exceeds the preset value.
The driving torque becomes more than the restraining torque consequently the disc rotates and
moving contact bridges the fixed contacts when the disc rotates through a pre-set angle.
Specification of over current relay
S.No. M292523
Model NO. CDG 31EG 1212 A5
Type Auxiliary voltage 220V D.C.
Manufacturer Jyoti Ltd. Baroda.
-
8/10/2019 thermal power plant bathinda
48/58
ELECTROSTATIC PRICIPITATOR (ESP)
Dust extractions from industrial gases become a necessity for environmental reasons. Most of the
plants in India use coal as fuel for generating steam. The exhaust gases contain large amount of
smoke and dust, which are being emitted into atmosphere. This poses a real threat to the mankind
as a dezarting health hazards. Hence it has become necessary to free the exhaust gases from smoke
and dust.
Need For Installation Of New Electrostatic Precipitator at GNDTP Units: -
The electrostatic precipitators installed at GNDTP units are designed to
give an emission level of 789 mg/NM3 for a coal having an ash content of not more than 30%.
However on actual testing it has been found that emission level from ESPs was about 3.0 mg/M3
.
The high level of emission is due to the fact that coals burnt in the boiler have much higher ash
content than what boilers are designed for. The pollution control board of Punjab Govt. has
specified an emission level of 380 mg/M3 from chimney. In order to achieve this new emission
level additional ESPs have been installed at GNDTP Bathinda.
-
8/10/2019 thermal power plant bathinda
49/58
Working Principle: -
The Electrostatic precipitator utilizes electrostatic forces to separate the dust particle form the gas
to be cleaned. The gas is conducted to a chamber containing Curtains of vertical steel plates.
These curtains divide the chamber into a number of parallel gas passages. The frames are linked to
each other to form a rigid framework.
The entire framework is held in place by four supports
insulators, which insulates it electrically from all parts, which are grounded.
A high voltage DC is applied between the framework and
the ground thereby creating a strong electrical field between the wires in the framework and the
steel curtains. The electrical field becomes strongest near the surface of the wire, so strong that an
electrical discharges. The Corona discharge is developed along the wires. The gas is ionized in
the corona discharge and large quantities of positive and negative ions are formed. The positivewires are immediately attracted towards the negative wires by strength of the field induced. The
negative ions however have to travel the entire space between the electrodes to reach the positive
curtains. On routes towards the steel curtains the ions collide with each other and get charged and
also this charge is transferred to the particles in the gas. The particles thereby become electrically
charged and also begin to travel in the same direction as the ions towards the steel curtains. The
electrical force on each particle becomes much greater than gravitational force. The speed of
migration towards the steel curtains is therefore much greater than the speed of sedimentation in
free fall.
-
8/10/2019 thermal power plant bathinda
50/58
PRINCIPLES OF ELECTROSTATIC PRECIPITATORS:-
a. Supplying high voltage between the Collecting Electrode and Discharge Electrode
generates a Corona Discharge that produce minor ions
b. The electrically discharged dust are attach towards the Collecting Electrodes by an
electrostatic force.
-
8/10/2019 thermal power plant bathinda
51/58
c. In case of dry electrostatic precipitators.
The accumulated dusts, due to the impact strength of hammer rapping to the Collecting
Electrodes are dropped and collected in the hopper.
d. In case of wet type electrostatic precipitators.
The dust is discharged in the hopper by flushing using a spray washing system.
e. The dust inside the hopper are discharged and transported by ash handling system.
-
8/10/2019 thermal power plant bathinda
52/58
General Description: -
There various parts of the precipitators are divided into two groups: -
Mechanical system comprising of casing, hoppers, gas distribution system, collecting and emitting
systems, rapping mechanism, stairway and galleries.
Electrical system comprising of transformer rectifier units with
Electronic Controller, Auxiliary Control Panels, Safety Interlocks and Field Equipment Devices.
1. Precipitator Casing: -
The precipitator casing is an all welded pre-fabricated wall and roof panels. The casing is
provided with inspection doors for entry into the chamber at each field. The doors are of
heavy construction with machined surface to ensure a gas tight seal.
The roof carries the precipitators internals, insulator housings, transformers etc. The
casing rests on roller a support which allows for free thermal expansion of the casing
during operating conditions. Galleries and stairway are provided on the sides of the casing
in easy access to rapping motors, inspection doors, transformers etc. walkways are
provided inside EP between fields for inspection and maintenance. The dust is collected in
large quantities on the curtains, the collected electrodes. Due to periodic rapping, the dust
falls into the hopper.
-
8/10/2019 thermal power plant bathinda
53/58
2. Hoppers:-
The hoppers are sized to hold the ash for 8 hrs. collection. Buffer plates provided in each
hopper to avoid gas leakage. Inspection door is provided on the one side of hoper wall.
Thermostatically controlled heating elements are arranged at the bottom portion of the
hopper to ensure free flow of ash.
3. Gas Distribution System: -
The good performance of the precipitators depends on the event distribution of gas over the
entire cross-section of the field. As the gas expands ten-fold while entering the precipitator,guide vanes, splitters and screens are provided in the inlet funnel to distribute the flue gas
evenly over the entire cross section of the EP.
-
8/10/2019 thermal power plant bathinda
54/58
4. Collecting Electrode system: -
The collecting plates are made of 1.6 mm cold rolled mild steel plate and shaped in piece
by roll forming. The collecting plates and shaped in one piece by roll forming. The
collecting electrode has unique profile with a special configuration on its longitudinal
edges. This profile is designed to give rigidity and to contain the dust in quiescent zone
free from re-entertainment; collecting plates are provided with hooks at their top edge for
suspension. The hooks engage in slot of the supporting angle. All the collecting plates in
arrow are held in position by a shock bar at the bottom. The shock bars are spaced by
guides.
5. Emitting Electrode system: -
The most essential part of precipitators is emitting electrode system. Four insulators
support this, the frames for holding the emitting electrodes are located centrally between
collecting electrodes curtains. The entire discharge frames are welded to form a rigid box
like structure. The emitting electrodes are kept between the frames.
-
8/10/2019 thermal power plant bathinda
55/58
6. Rapping System: -
Rapping mechanism is provided for collecting and emitting electrodes. Geared motors
drive the rapping mechanism. The rapping system employs tumbling hammers, which are
mounted on a horizontal shaft. As the shaft rotates slowly the hammers which are mounted
on a horizontal shaft. As the shaft rotates slowly the hammers tumble on the shock
bar/shock, which transmits blow to the electrodes. One complete revolution of the rapping
shaft will clean the entire field. The rapper programmer decided the frequency of rapping.
The tumbling hammers disposition and the periodicity of the rapping are selected in such a
way that less than 2% of the collecting area is rapped one time. This avoids re-
entertainment of dust and puffing at the stock outlet.
The rapping shaft of emitting electrodes system is electrical isolated from the geared motor
driven by a shaft insulator. The space around the shaft insulator is continuously heated to
avoid condensation.
7. Insulator Housing:-
The support insulator, supporting the emitting electrodes system is housed in
insulator housing. The HVDC connection is taken through bushing insulator mounted onthe housing wall. In order to avoid the condensation on the support insulator each insulator
is provided with one electrical heating system elements of one pass are controlled by one
thermostat.
-
8/10/2019 thermal power plant bathinda
56/58
Following Are the Modules For The Outgoing Feeders: -
Hopper heater for each field
Support insulator heaters.
Shaft insulator heaters.
Collecting electrode-rapping motor for each field.
Emitting electrode rapping motor for each filed.
The performance of the ESP is influenced by a number of factors many of which may be
controllable. It should be the aim of every operator to maximize the performance by judiciously
adjusting the controllable variables.
Cleaning Of Electrodes: -
The performance of the ESP depends on the amount of electrical power absorbed by the system.
The highest collection efficiency is achieved when maximum possible electric power for a given
set of operating conditions is utilized on the fields. Too thick a dust layer on the collecting plates
will lead to drop in the effective voltage, which consequently reduces the collection efficiency. It
also leads to unstable to unstable operating conditions. Therefore the rapping system of collecting
and emitting electrodes should be kept in perfectly working condition. All the rapping motors havebeen programmed to achieve the optimum efficiency.
Spark Rate: -
The operating voltage and current keep changing with operating conditions. The secondary current
of HVRs have been set just below the spark level, so that only few sparks occur during an hour.
Spark rate between 5 to 10 sparks per minute is the most favorable limit, as per the practical
experience. Too high flash over will not only result in reduction in useful power and interruption
of precipitation process but will cause snapping of emitting electrodes due to electrical erosion.
-
8/10/2019 thermal power plant bathinda
57/58
How To Control The Spark Rate: -
One number s-pot and one number t-pot have been provided on the front of each electronic
controller. The s-pot controls the drop rate of rise of field current after the spark is over. The
operator can control the rate of spark by adjusting these two pots manually. Both the pots if turned
anticlockwise will cause increase in spark rate.
Ash Hopper Evacuation: -
Improper/incomplete hopper evacuation is a major cause for the precipitator malfunction. If the
hoppers are not emptied regularly, the dust will build up to the high tension emitting system
causing shot circuiting. Also the dust can push the internals up causing misalignment of the
electrodes. Though the hoppers have been designed for a storage capacity of 8 hours, under MCRconditions, this provision should be used in case of emergency. Normally, the hopper should not
be regarded as storage as storage as storage space for the collected ash.
Oil combustion: -
The combustion of oil used during start up or for stabilization of the flames can have an important
impact on precipitator operation. Un burnt oil, if passed into ESP can deposit on the emitting and
collecting electrodes and deteriorates the electrical condition i.e. reduce the precipitators operating
voltage due to high electrical resistivity and consequently the ESPs performance is affected
adversely. The precipitator performance remains poor until the oil vaporizes and the ash layer gets
rapped off, which usually takes along time.
Air Conditioning of the ESPs Control Room: -
The ESPs control room houses sophisticated electronic controller. The operation of these
controllers directly reflects on precipitator performance. In order to ensure that the controllers are
in proper working conditions, it is essential to maintain a dust free atmosphere with controlled
ambient conditions. Therefore, the air conditioners should be kept in proper working conditions.
-
8/10/2019 thermal power plant bathinda
58/58