thermal power plant bathinda

8/10/2019 thermal power plant bathinda

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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


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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.


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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.


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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


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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.


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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.


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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)


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STEAM TURBINE:-


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:-


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:-


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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:-


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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


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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


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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.


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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.


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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


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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


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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.


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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.


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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:-


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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


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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


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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
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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.


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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.


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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.


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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


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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


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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


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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


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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


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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)


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TURBINE SPECIFICATIONS:-


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.


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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


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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.


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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.


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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


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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


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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


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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


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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.


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(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.


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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.


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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.


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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.


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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


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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.


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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.


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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.


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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.


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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.


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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.


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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.


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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.


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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.


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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.


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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.


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