Summer Training in badarpur ntpc

7/27/2019 Summer Training in badarpur ntpc

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INTRODUCTION

National Thermal Power Corporation Limited was formed in 1975 to plan,

promote and organize an integrated and efficient development of Central

Sector Power Stations.

The Singrauli Super Thermal Power Station was the first of the series of

pithead power stations along with 400kV ac transmission line network. It is

located on the banks of Govind Ballabh Pant Sagar (Rihand Reservoir),

about 200km south of Varanasi in the Sonebhadra district of Uttar Pradesh.

For coal transportation, a captive railway system with rapid loading and

unloading facility known as Merry-Go Round (MGR), continuously hauls

coal from the Jayant block of Singrauli coalfields to the plant site. The rake

consists of 30 wagons and will deliver 1800 MT of coal in each cycle. The

average daily consumption of coal is 25,000 MT per day i.e. 8.0 million

tonnes per annum considering average calorific value of 4000 kcal/kg and

7000 hrs of operation in an year for the ultimate capacity of the plant of

2000 MW having 5 units of 200 MW each and 2 units of 500 MW each.

The 5200MW generating units of Stage I are each equipped with coal-

fired, regenerative, re-heat type steam generators with electrostatic

precipitators, each generating 700 tonnes/hr of steam at 138 kg/cm 2 pressure

and 535C temperature. The steam generator feeds steam to a condensing,

horizontal, tandem compound 3-cylinder re-heat type turbo generator

rotating at 3000 rpm and each generates 200 MW. Three phase generator

transformer of 250 MVA capacity steps up the generation voltage from

15.75 KV to 400 KV.

Cooling water from the Rihand Reservoir is drawn through an approachchannel. It is then pumped into concrete intake duct by vertical pumps of

15000 m 3/hr capacity each. From the ducts, the water is circulated through

condensers and is then discharged into a duct from where it flows into an

open channel. This open channel carries the water for a distance of 6 kms to

affect sufficient cooling before it joins back into Rihand Reservoir.

The 2500MW generating units of Stage II are each equipped with coal-

fired, regenerative, re-heat type steam generators with electrostatic


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Circulating water system Ash handling system Compressed air system Hydrogen generating plant

Growth of NTPC:

Fig: figure of growth rate

NTPC was ranked 3rd

best employer and the No.1 Public sector undertaking

among 220 major companies in India by Business Today Hewitt

Association Best Employers Survey 2003.

COAL TO STEAM STEAM TO MECHANICAL POWER


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MECHANICAL POWER TO ELECTRICITY SWITCHING AND TRANSMISSION

COAL TO STEAM

Coal from the coal wagons is unloaded in the coal handling plant. This coal

is transported upto the raw coal bunkers with the help of belt conveyors.

Coal is transported to bowl mills by coal feeders. The coal is pulverized in

the bowl mill, where it is ground to a powder form. The mill consists of a

round metallic table on which coal particles fall. This table is rotated with

the help of a motor. There are three large steel rollers, which are spaced 120

apart. When there is no coal, these rollers do not rotate but when the coal is

fed to the table it packs up between the roller and the table and this forces

the roller to rotate. Coal is crushed by the crushing action between the rollers

and the rotating table. This crushed coal is taken away to the furnace through

coal pipes with the help of hot and cold air mixture from the primary air

(P.A.) fan. The P.A. fan takes atmospheric air, a part of which is sent to the

air preheaters for heating while a part goes directly to the mill for

temperature control. Atmospheric air from forced draft (F.D.0 fan is heatedin the air heaters and sent to the furnace as combustion air.

Water from the boiler feed pump passes through economiser and reaches the

boiler drum. Water from the drum passes through down comers and goes to

bottom ring header. Water from the bottom ring header is divided to all the

four sides of the furnace. Due to heat and the density difference water rises

up in the water wall tubes. Water is partly converted into steam as it rises up

in the furnace. This steam and water mixture is again taken to the boiler

drum where the steam is separated from water. Water follows the same path

while steam is sent to the superheaters for superheating. The superheaters

are located inside the furnace and the steam is superheated (540C) and

finally goes to the turbine.

Flue gases from the furnace are extracted by the induced draft (I.D.) fan,

which maintains a balanced draft in the furnace with F.D. fan. These flue

gases emit their heat energy to various superheaters in the plant house and

finally pass through the air preheaters and goes to the electrostatic

precipitator where the ash particles are extracted. Electrostatic precipitators


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consist of metal plates, which are electrically charged. Ash particles are

attracted to these plates, so that they do not pass through the chimney to

pollute the atmosphere. Regular mechanical hammer blows cause theaccumulation of ash to fall to the bottom of the precipitator where they are

collected in a hopper for disposal. This ash is mixed with water to form

slurry and is pumped to ash dyke.

STEAM TO MECHANICAL POWER

From the boiler, a steam pipe conveys steam to the turbine through a stop

valve (which can be used to shut off steam in an emergency) and through

control valves that automatically regulate the supply of steam to the turbine.Stop valves and control valves are located in the steam chest and a governor,

driven from the main turbine shaft, operates the control valves to regulate

the amount of steam used (this depends upon the speed of the turbine and the

amount of electricity required from the generator).

Steam from the control valves enters the high pressure cylinder of the

turbine, where it passes through a ring of stationary blades fixed to the

cylindrical wall. These act as nozzles and direct the steam into a second ring

of moving blades mounted on a disc secured to the turbine shaft. Thissecond ring turns the shafts as a result of the force of the steam. The

stationary and moving blades together constitute a stage of the turbine and

in practice many stages are necessary, so that the cylinder contains a number

of rings of stationary blades with rings of moving blades arranged between

them. The steam passes through each stage in turn until it reaches the end of

the high pressure cylinder and in its passage some of its heat energy is

changed into mechanical energy.

The steam leaving the high pressure cylinder goes back to the boiler for

reheating and returns by a further pipe to the intermediate pressure cylinder.Here it passes through another series of stationary and moving blades.

Finally, the steam is taken to the low pressure cylinders, each of

which it enters at the center flowing outwards in opposite directions

through the rows of turbine blades an arrangement known as double

flow to the extremities of the cylinder. As the steam gives up its heat

energy to drive the turbine, its temperature and pressure fall and it


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expands. Because of this expansion the blades are much larger and

longer towards the low pressure end of the turbine.

The turbine shaft usually rotates at 3,000 rpm. This speed is determined by

the frequency of the electrical system used in the country. In India, it is the

speed at which a 2- pole generator is driven to generate alternating current at

50 Hz.

When as much energy as possible has been extracted from the steam it is

exhausted directly to the condenser. This runs the length of the low pressure

part of the turbine and may be beneath or on either side of it. The condenser

consists of a large vessel containing some 20,000 tubes, each about 25 mm

in diameter. Cold water from the water source i.e. the Rihand Reservoir iscirculated through these tubes and as the steam from the turbine passes

round them it is rapidly condensed into water condensate. Because water has

a much smaller comparative volume than steam, a vacuum is created in the

condenser. This allows the steam pressure to reduce down to pressure below

that of the normal atmosphere and more energy can be utilized.

From the condenser, the condensate is pumped through low pressure heaters

by the extraction pump, after which its pressure is raised to boiler pressure

by the boiler feed pump. It is further passed through feed heaters to theeconomiser and the boiler for reconversion into steam.

The cooling water drawn from the reservoir is returned directly to the source

after use.

MECHANICAL POWER TO ELECTRICITY

The turbine shaft is mechanically coupled to the generator rotor shaft

through thrust bearings. The steam rotates the turbine at 3000 rpm thus the

rotor of the generator also rotates at 3000 rpm. This speed is necessary to

generate electricity at a frequency of 50 Hz with a two pole turbo- generator.


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The rotor carries the field winding over it. This field winding is excited by a

DC excitation system. The supply to the excitation system is tapped from the

unit auxiliary transformer. The flux generated by this field current cuts thearmature coil. The armature coil is star- star connected and is induced with

three phase emf. The emf is tapped with the help of slip rings and brushes.

This emf is carried over to the generator transformer through a bus duct. The

bus duct is voltage transformer grounded.

The generator transformer has delta connection in the primary side and star

connection in the secondary side. The generator bus supplies electric power

per phase to the three-phase transformer or bank of three single-phase

transformers. These transformers transmit electric power to the switchyard

for further transmission. These transformers also supply the unit auxiliarytransformers required for the working of various electric motors, pumps and

other equipments installed in the unit.

SWITCHING AND TRANSMISSION

The electricity is usually produced in the stator windings of large moderngenerators and is fed through terminal connections to one side of a generator

transformer that steps up the voltage to 400KV. From here conductors carry

it to a series of three switches comprising of an isolator, a circuit breaker and

another isolator.

The circuit breaker, which is a heavy- duty switch capable of operating in a

fraction of second, is used to switch off the current flowing to the

transmission lines. Once the current has been interrupted the isolators can be

opened. These isolate the circuit breaker connected to its terminals. Here

after the maintenance or repair work can be carried out safely.

From the circuit breakers the current is taken to the busbar conductors,

which run the length of the switching compound and then to another

circuit breaker with its associated isolators, before being fed to the Grid.

Each generator in a power station has its own transformer, circuit breaker

and associated isolators but the electricity generated is fed into a common

set of busbars.


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Circuit breakers work like combined switches and fuses but they have

certain special features and are very different from the domestic switch and

fuse. When electrical current is switched off by separating two contacts, anarc is created between them. At the voltage use in homes, this arc is very

small and lasts for a fraction of a second but at very high voltages used for

transmission, the size and power of the arc is considerable and it must be

quickly quenched to prevent damage.

Three phase, four-wire system is used for large power transmission, as it is

cheaper than the single-phase two-wire system that supplies the home. Also

power is generated in a three-phase system.

The center of the power station is the control room. Here the engineersmonitor the output of electricity, supervising and controlling the operation of

generating plant and high voltage switchgear and directing power to the grid

system as required. Instruments on the control panels show the output and

the existing condition of the whole main plant and a miniature diagram

indicates the precise state of the electrical system.

COAL HANDLING PLANT STEAM GENERATOR TURBINE TURBO- GENERATOR SWITCHYARD


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CONTROL & INSTRUMENTATIONAUXILIARY POWER DISTRIBUTION SYSTEM WATER TREATMENT PLANT CIRCULATING WATER SYSTEMASH HANDLING SYSTEMHYDROGEN GENERATING PLANT

COAL HANDLING PLANT

It is estimated that the coal required for a 2000MW Super Thermal Power

Station is of the order of 8.4 million tonnes based on an average calorific

value of 4000 kcal/kg and 7000 hours of operation per year.

Two coal handling systems one for 5200MW units and the second for

2500MW units have been provided. The capacity of each of the two

conveying systems has been kept as 1200 tonnes/hour. Interconnection


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between the two coal handling systems has also been provided to transfer

crushed coal from one crusher house to the other.

The Merry-go Round (MGR) system has been provided for loading the coal

at the Jayant mines and unloading the coal into the track hopper

automatically when the wagons are moving at a predetermined speed of

8km/hr. A closed loop of rail lines has been laid between the loading and

unloading points and a rake of 30 bottom discharge type wagons of 60

tonnes capacity each transport coal of size 0 to 200mm from mines and

unload it into track hopper in 10 minutes. Automatic bottom opening type

wagons discharge coal into track hopper while the rake travels over the

hopper, the discharge door being automatically opened by a line sidetripping mechanism. The coal received at the track hopper is delivered to

two parallel conveyors 1A &1B located on the sides through four nos. of

rotary plough paddle feeders designed to handle maximum coal lump size of

200mm. Double stream of conveyor system carries the coal to the crusher

house, having four nos. crushers and vibrating screens each having a

capacity of 600T/hr. The coal after being crushed from 200mm to 20mm

size is conveyed to the boiler bunkers. The width of the conveyor belt is kept

1400mm. The crushed coal from the crusher house, if not required, is

stacked in the open stock yard. Two nos. of stacker cum reclaimer areprovided on rail track to handle maximum 20mm size coal lumps and have a

capacity of 1200T/hr.

Paddle FeedersFour nos. of traveling paddle feeders are provided to collect coal from the

track hopper. They travel along the entire length of the hopper and transfer

the coal from the hopper, uniformly to the pair of underground conveyors

1A &1B. The paddle feeders move to and fro on the rail with the help of 4

nos. of wheel mounted on the supporting structures. The wheels are drivenby electric motor of 415V supply.

Belt Conveyor SystemThe belting system is designed for conveyor capacity of 1200T/hr and belt

speed of 2.6metre/sec. The belt is of cotton fabric with rubber covers of

adequate strength having width of 1400mm.


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Magnetic SeparatorsThis is an electromagnet placed above the conveyor to attract magnetic

materials. Over this magnet there is one conveyor to transfer these materialsto chute provided for dumping at ground level. Because of this, continuous

removal is possible and it is also not necessary to stop the electric supply to

the magnetic separators for removal of separated material.

Stacker and ReclaimerTwo nos. of traveling stacker/reclaimer each capable of both stacking and

reclaiming are installed which operate on rail tracks running for adequate

length to cover the entire coal storage yard. The belt of the stacker/reclaimer

is mounted on a cantilever boom and has a capacity of 1200T/hr for bothstacking and reclaiming. The boom can revolve about the center of the

receiving hopper and discharge/reclaim materials on/from both sides of the

track anywhere between 28 meters radius of the boom. These units work in

conjunction with the conveyor 9A & 9B.

Crusher HouseThe plant has four nos. of crushers each capable of crushing coal of 200mm

size at the rate of 600T/hr. the crusher with hammer tips is symmetrical in

size and shape on either side. In case of wearing out of one side, the othercan be used by turning over the tips. These crushers are placed in the crusher

house, which have special strong foundations to bear the vibrations due to

running of the crushers.

Vibrating FeederThe vibrating feeder is used for throwing the coal on the underground

conveyor belt from where coal goes to the bunker. Coal from the stockyard,

with the help of bulldozer, is taken to the vibrating feeder via reclaimer

hopper and underground conveyor belt. In case the bunker requirement ismore than the capacity of crusher or stacker reclaimer, then with the help of

bulldozer the coal is sent to the bunker from the stockyard, through these

feeders.


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STEAM GENERATOR

The steam generator used in Stage I of SSTPS has a primary steam flow of

700 tonnes/hr at 139 kg/cm 2 pressure and 535C temperature at the

superheater outlet. This boiler is tangentially fired, has balanced draft,

natural circulation, radiant single reheat, dry bottom open door type and is

direct fired with Indian bituminous pulverized coal. The steam generator

used in Stage II of SSTPS has a primary steam flow of 1725 tonnes/hr at 178

kg/cm 2 pressure and 540C temperature at the superheater outlet. This boiler

is balanced draft, controlled circulation, dry bottom single drum type and is

direct fired with Indian bituminous pulverized coal.

The arrangement of main boiler and its accessories is as follows:

The boiler structural are divided into two parts:

Supporting Structures:Boiler supporting structure consists of a systematic arrangement of columns

stiffened with horizontal beams and vertical diagonal bracings and comprise

of low carbon steel material. It is composed of 18 main columns and 12

auxiliary columns. The main columns support the main boiler components

viz. drum, water wall membrane, panels, superheaters, reheaters,

economisers, air preheater, burners and galleries at various levels. The

auxiliary columns support the boiler platforms and other ducts coming inthat region. The total weight of supporting structures is about 970 M.T.

Galleries and Stairways:Galleries and stairways around the combustion and heat recovery areas are

provided for proper approach to the boiler. Stairways on both the sides of the

boiler are provided. All the floors are covered with the floor gratings of

required depth for walkway and are welded to the structure. Their total

weight is 900 M.T.


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FurnaceA boiler furnace is that space under or adjacent to a boiler in which fuel isburned and from which the combustion products pass into the boiler proper.

It provides a chamber in which combustion reaction can be isolated and

confined so that the reaction remains a controlled force. In addition it

provides support or enclosure for the firing equipment.

In stage I, fusion welded furnace is used and in stage II controlled

circulation furnace is used.

Boiler DrumThe function of the boiler drum is to separate water from the steam

generated in the furnace walls and to reduce the dissolved solid contents of

the steam to below the prescribed limit of 1 ppm. The drum is located on the

upper front of the boiler.

In stage I, the drum weighs about 127 MT is apporx.15.7 m. long and is

placed at a height of 53340 mm. It is made of carbon steel. It is designed for

maximum pressure of 176 kg/cm 2 and maximum metal temperature of

354C. In stage II, the drum is 22.07 m. long and is placed at a height of 72m. It is made of carbon steel. It is designed for maximum pressure of 204.9

kg/cm 2 and maximum metal temperature of 366C.

SuperheaterSuperheater is meant to raise the temperature of saturated steam by

absorbing the heat from flue gases and thus increases the cycle efficiency

economically. There are three stages of super heater besides the sidewalls

and the extended walls. The first stage consists of horizontal superheater of

convection mixed flow type with upper and lower bank located aboveeconomiser assembly in the rear pass. The upper bank terminates into hanger

tubes, which are connected to outlet header of the first stage superheater.

The second stage superheater consists of pendant platen, which is of radiant

parallel flow type. The third stage superheater pendant spaced is of

convection parallel flow type.

In Stage I, the primary steam flow is 700 tonnes/hr at 139 kg/cm 2 pressure

and 535C temperature at the superheater outlet. In Stage II, the primary


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steam flow is 1725 tonnes/hr at 178 kg/cm 2 pressure and 540C temperature

at the superheater outlet.

AttemperatorAttemperation or desuperheating is the reduction or removal of superheat

from steam to the extent required. The characteristic performance of a

superheater, which receives its heat by convection from gases flowing over

it, is raising temperature with increasing output. To obtain some degree of

control, the superheater must be designed for full temperature at some partial

load. As a result, there will be excessive surface, with corresponding

excessive temperatures at higher loads. Attemperator is used to reduce the

steam temperature.

EconomiserThe purpose of the economiser is to preheat the boiler feed water before it is

introduced into the steam drum by recovering heat from the flue gases

leaving the boiler. The economiser is located in the boiler rear gas pass

below the rear horizontal superheater. The economiser is continuous loop

type, without fins, and water flows in upward direction and gas in the

downward direction.

A single stage of economizer is used to absorb the heat from the flue gases

and add this as sensible heat to the feed water before it enters into boiler

drum. The economizer is non-steaming continuous plain tube type and of

tubular construction.

ReheaterA single reheat system is used to further increase the efficiency of the cycle

by raising the temperature of already expanded steam. After passing through

the high-pressure stage of the turbine, steam is returned to the reheated bytwo cold reheat lines. After being reheated to the designated temperature, the

reheated system at 535 degree Celsius temperature and 24.5 kg/sq. cm

pressure is returned to the intermediate pressure stage of the turbine via the

hot reheat line.

BurnersIn stage I, there are total twenty four pulverized coal burners for corner fired

boilers and twelve oil burners provided each in between two pulverized fuel


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burner. The pulverized coal burners are arranged in such a way that the six

mills supply the coal burners at four corners of the furnace.

In stage II, there are total thirty-two pulverized coal burners for corner fired

boilers and sixteen oil burners provided each in between two pulverized fuel

burner. The pulverized coal burners are arranged in such a way that the eight

mills supply the coal burners at four corners of the furnace.

IgnitersThere are twelve side igniters per boiler in stage I and sixteen in stage II.

The atomizing air for the igniter is taken from the service air compressors.

The burners are located at three elevations in stage I and four elevations instage II. Each elevation has four oil burners and igniters. These elevations

are normally referred to as AB elevation, CD elevation, EF elevation and

GH elevation. Igniters are used for lighting the main oil gun. There are two

igniter air fans to supply air for combustion of igniter oil.


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The arrangement of various boiler auxiliaries is as follows:

Coal BunkerThese are in- process storage silos used for storing crushed coal from the

coal handling system. Generally, are made up of welded steel plates. There

are six such bunkers supplying coal to the corresponding mills in stage I and

eight in stage II. These are located on top of the mills so as to aid in gravity

feeding of coal.

Coal FeederEach mill is provided with a drag link gravimetric feeder to transport raw

coal from the bunker to the inlet chute, leading to mill at desired rate. Coalfeeders are essential as the mills do not have any storage provision therefore

only that much coal should be sent to the mill that has to be directly sent to

the furnace and this is decided by the load requirement.

MillsThere are six mills in stage I, out of which five are required for operation at

maximum load and one acts as standby. In stage II, there are eight mills and

here six are required for operation and two act as standby. These are located

adjacent to the furnace at 0 m level. These mills pulverize the coal to thedesired fineness to be fed to the furnace for combustion.

Primary Air FanPrimary air fan is used to supply primary air to transport the pulverized coal

from the mills/bunkers to the furnace and to dry up the coal in the path.

There are two PA fans per unit and are designed to handle atmospheric air

upto a temperature of 50C. These fans are driven by a 6.6KV motor each.

They are located at 0 m level near the boiler.

Air PreheaterAir preheater transfers heat from the flue gases to the cold primary and/ or

secondary air by means of rotating heating surface elements. Beneath these

regenerative type air preheaters, there exists a steam coil air preheater. These

are located in the secondary pass of the furnace at a height of around 16 m

level. Each unit has two such air preheaters.


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Forced Draft FanThe FD fan is designed for handling secondary air for the boiler. These fans

are located at 0 m level near the PA fan. The fan is coupled with an 800Winduction motor and is commissioned to drive the cold air through the air

preheater.

Wind BoxThese act as distributing media for supplying secondary/ excess air to the

furnace for combustion. These are generally located on the left and right

sides of the furnace while facing the chimney.

Scanner Air FanScanner fans are installed in the boiler for supplying continuously cooling

air to the flame scanner provided for flame supervision. Normally one fan

remains in service while the other one remains available as standby.

Igniter Air FanIgniter fan provides necessary combustion air to all the igniters. Fan makes

the suction from atmosphere directly and supplies air to the wind boxes of

individual igniters at a fixed constant uncontrolled rate at ambient

temperature.

Electrostatic PrecipitatorTwo ESPs have been set up for each generating units to remove the major

part of fly ash. Each ESP has 304 electrodes made of steel sheets. Between

each pair of electrodes a unidirectional high voltage of 60kV is applied,

connecting its negative polarity to emitting electrodes and positive to

collecting electrodes. The flue gases that are normally neutral when pass

between rows of these electrodes are ionized due to the emitting and the

negative towards the collecting electrodes. Since dust particles have great

affinity towards negative particles they get attached to them and are thus

negatively charged. Thus the dust particles are deposited on the collecting

electrodes and are dislodged from there by periodic rapping of electrodes

and are drained to the ash disposal system through hoppers.


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Induced Draught FanInduced draught fan is used to drive the waste flue gases out of the chimney

after they have been deprived almost all of their heat energy. A 1300 kWinduction motor is used to drive this fan. The major part of the energy

transferred to the gas is the velocity energy after the impeller. The velocity

energy is converted into pressure energy by the diffuser. Flow is controlled

by changing the direction of gas entry to the impeller blades by providing

adjustable guide vanes.

Fig: induced draft fan

ChimneyThese are tall RCC structures with single or multiple flues. The height of

these chimneys helps in natural draught of the flue gases to the atmosphere.

There are four chimneys in SSTPS- one for units 1, 2 and 3, second for units


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4 and 5 and one each for units 6 and 7.

Fig: figure of chimney

Seal Air FanThese are used for supplying seal air to the mills to prevent ingress of coal

dust into gearbox lubrication oil. There are two fans per boiler.


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Soot Blowers

The soot blowers are used for efficient on-load cleaning of furnace,


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superheaters, reheaters and regenerative air heaters. There are three types of

soot blowers provided in the plant in requisite numbers. They are:

1. Long retractable soot blowers2. Wall blower3. Air heater blower

Superheated steam is tapped from the superheater for the purpose of soot

blowing.

In stage I, there are 20 long retractable soot blowers, 56 wall blowers and 2

air heater blowers and in stage II, there are all together 104 soot blowers. All

these soot blowers are operated together once in every eight hours for few

minutes only.

TURBINE

A steam turbine has two main parts viz. the cylinder and the rotor. The

cylinder (stator) is a cast iron or steel housing usually divided at the

horizontal centerline. Its halves are bolted together for easy access. The

cylinder contains fixed blades, vanes and nozzles that direct steam into

moving blades carried by the rotor. Each fixed blade set is mounted in

diaphragms located in front of each disc on the rotor, or directly in the

casing. A disc and diaphragm together make a turbine stage. Steam turbine

can have many stages. The rotor is a rotating shaft that carries the moving

blades on the outer edges of either drums or discs. The blades rotate as the

rotor rotates. The rotor of a large steam turbine consists of high, intermediate

and low pressure sections.

In a multiple stage turbine, steam at a high pressure and high temperature

enters the first row of fixed blades or nozzles through an inlet valve or

valves. As the steam passes through the fixed blades or nozzles it expands

and its velocity increases. The high velocity jet of steam strikes the first set

of moving blades. The kinetic energy of the steam changes into mechanicalenergy, causing the shaft to rotate. The steam then enters the next set of

fixed blades and strikes the next row of moving blades.


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As the steam flows through the turbine, its pressure and temperature

decreases, while its volume increases. The decrease in pressure and

temperature occurs as the steam transmits energy to the shaft and performs

work. After passing through the last turbine stage, the steam exhausts into

the condenser or process steam system.

ROTOR OF H.P. TURBINE


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Large turbines use both impulse and reaction types. These combination

turbines have impulse blades at the high pressure end and reaction blades atthe low pressure end. The blade length and size increases throughout the

turbine to use the expanding steam efficiently. Blade rows require seals to

prevent steam leakage where the pressure drops. Seals for impulse blades are

provided between the rotor and the diaphragm to stop leakage past the

nozzle. Seals for reaction blades are provided at the tips of both the fixed

and moving blades.

In stage I, condensing, tandem reheat, impulse type turbine is installed. The

HP cylinder has 12 stages, IP cylinder has 11 stages and LP cylinder has 42

stages. The HP and IP parts are single flow cylinders and the LP part has

double flow cylinder.

In stage II, 3 cylinder, reheat, reaction type turbine is installed. The HP

cylinder has 18 stages, IP cylinder has 142 stages and LP cylinder has 62

stages. The HP part is a single- flow cylinder and the IP and LP parts are

double flow cylinders.

The arrangement of various turbine auxiliaries is as follows:

Vacuum systemThis system comprises of condenser, ejector, CW pump and gland steam and

gland steam coolers. The equipments under this system strive to maximize

the work done of turbine by maintaining the rated vacuum limits.

Condenser: There are two condensers entered to the two exhausters of the

LP turbine. These are surface type condensers with two-pass arrangement.

Cooling water is pumped into each condenser by a vertical CW pump

through the inlet pipe. Steam exhausted from the LP turbine by washing theoutside of the condenser tubes losses its latent heat to the cooling water and

is connected with water in the steam side of condenser. This condensate

collects in the hot well, welded to the bottom of the condensers.

Ejectors: there are two 100% capacity ejectors of the steam eject system.

The purpose of the ejector is to evacuate air and other non-condensing gases

from the condensers and thus maintain the vacuum in the condensers.

C.W. Pumps: the pumps which supply the cooling water to the condensers

are called the circulating water pumps. There are two such pumps in each


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unit. These pumps are normally vertical, wet-pit, mixed flow type, designed

for continuous heavy duty.

Condensate System:The steam after condensing in the condenser known as condensate is

extracted out of the condenser hot well by condensate pump and taken to the

deaerator through ejectors, gland steam cooler and series of LP heaters. This

comprises of condensate pumps, low pressure heaters and deaerator.

Condensate Pumps: the function of these pumps is to pump out the

condensate to the deaerator through ejectors, gland steam coolers and LP

heaters. These pumps have four stages and since the suction at a negativepressure, special arrangements have been made for providing sealing.

L.P. Heaters: Turbine has been provided with non-controlled extractions

which are utilized for heating the condensate, from turbine bleed steam.

There are 4 LP heaters in which the last four extractions are used.

Deaerator: The presence of certain gases, principally oxygen, carbon

dioxide and ammonia, dissolved in water is generally considered harmful

because of their corrosive attack on metals, particularly at high temperatures.

The function of the deaerator unit is to remove dissolved gases from the

boiler feed water by mechanical means.

Feed Water System:This system helps in the supply of feed water to the boiler at requisite

pressure and steam/ water ratio. This system comprises of boiler feed pumps,

high pressure heaters and drip pumps.

Boiler Feed Pump: The function of the boiler feed pump is that the water

with the given operating temperature should flow continuously to the pumpunder a certain minimum pressure. It passes through the suction branch into

the intake spiral and from there is directed to the first impeller. After leaving

the impeller it passes through the distributing passages of the diffuser and

thereby gets a certain pressure rise and at the same time it flows over to the

guide vanes to the inlet of the next impeller. This will repeat from one stage

to the other till it passes through the last impeller and the end diffuser. Thus

the feed water reaching into the discharge space develops the necessary

operating pressure.


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There are three boiler feed pumps in each unit in SSTPS. Two of these are

turbine driven while one, which is a stand by is motor driven. The feed

pump motor, which is the biggest motor in the whole plant, is a 9800 Winduction motor.

H.P. Heaters: These are regenerative feed water heaters operating at high

pressure and located by the side of turbine. These are generally vertical type

and turbine bleed steam pipes are connected to them. HP heaters are

connected in series on feed water side and by such arrangement, the feed

water, after feed pump enters the HP heaters.

Drip Pump: The steam that bleeds from the turbine after condensation is

termed as drip/ drain. Two numbers of sectional multistage centrifugal

horizontal pumps per unit are provided. Out of these one will be running and

other is standby. These are especially suited for the purpose of pumpingfrom the space of high vacuum.

Turbine Lubricating Oil System:Turbine lub- oil system seeks to provide proper lubrication of turbo-

generator bearings and operation of barring gear. This consists of main oil

pump (MOP), starting oil pump (SOP), AC standby oil pumps and

emergency DC oil pump and jacking oil pump (JOP).

Main Oil Pump: This is coupled with turbine rotor through a gear

coupling. When the turbine is running at normal speed i.e. 3000 rpm or the

turbine speed is more than 2800 rpm, then the desired quantity of oil to the

governing system and to the lubrication system is supplied by this oil pump.

Starting Oil Pump: It is a multistage centrifugal oil pump driven by AC

electric motor. Starting oil pump is provided to meet the oil requirement of

the turbo- set during starting and stopping. It also serves as stand by to main

oil pump.

AC Standby Oil Pump: This is a centrifugal pump driven by an AC electricmotor. It runs for 10 minutes in the beginning to remove air from the

governing system and fill the oil system with oil. This pump automatically

takes over under interlock condition when the oil pressure falls below a

certain standard level. Thus this pump meets the requirement of lubrication

system under emergency conditions.

Jack Oil Pump: This pump enables the main bearing of the complete rotor

assembly to be raised or floated in the bearing during turbine generator start

up and during shut down, thus preventing damage to the bearings when shaft


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speeds are too low for hydrodynamic lubrication to take place. This pump

takes suction from the main oil tank and after lifting the bearing the drain is

connected back to the main oil tank.Oil Coolers: The oil of the lubrication and the governing systems is cooled

in the oil coolers. The cooling medium for these coolers is circulating water.

The pressure of the cooling is kept lower than that of oil to avoid its mixing

with oil if the tubes rupture. There are five oil coolers out of which four are

for continuous operation and one remains as standby. All the oil coolers are

arranged to operate in parallel. The cooling water temperature is not more

than 36C.

Auxiliary Steam System:Some of the thermal cycle equipments/ systems require steam for primaryheating, actuation, sealing etc. This requirement is met by the auxiliary

steam system.


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TURBO-GENERATOR

The turbo-generator essentially consists of a fixed stator and a revolving

rotor. The stator core carries a three phase winding in which alternating emf

is induced, the rotor carrying field magnets and coils which provide the

magnetic flux of the machine, set up by exciting the generator field current.

The turbo-generator, one no. for each unit is of three phase, two-pole

cylindrical rotor type which is directly driven by a steam turbine, at

3000RPM.

These generators have direct water-cooling for the stator winding and directhydrogen cooling for the rotor winding. The stator frame consists of a

cylindrical center section and two end shields, which are gas tight and

pressure resistant. It accommodates the electrically active parts of the stator

i.e. the stator core and stator winding. The stator winding consists of a

double layer, short-pitched lap winding with 540 transposition. The rotor

shaft is a single solid forging. On the forged round rotor, slots are milled out

to insert and secure the conductors of the generator excitation windings.

Rotor windings consist of two cooling ducts and L-shaped strips of

laminated insulator for slot insulation.

The field current is supplied to the rotor winding through radial terminal

bolts and two semi-circular conductors located in the hollow bores of the

exciter and rotor shafts. The field current leads are connected to the exciter

leads at the exciter coupling with Multi Kontakt plug-in contacts, which

allow for unobstructed thermal expansion of the field current leads.

The nameplate specifications of the generators are as follows:

Generator# 1 to 5:MakeM/s BHEL

Rated output200 MW/ 235 MVA

Power factor0.85 lag

Frequency50 Hz

Terminal voltage15.75 KV

Speed.3000 rpm

Stator current.9050A

Hydrogen pressure3.5 kg/cm 2


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Field current..2600 A

No. of terminals brought out. Six (6)

Generator# 6&7:Make..M/s KWU, Germany

Supplied byM/s BHEL

Type ..THDF 115/59

Rated output..500MW/ 588MVA

Power factor..0.85(lag)

Frequency..50Hz

Terminal voltage21KV

Speed.3000RPMStator current.16,200A

Hydrogen pressure.4 kg/cm 2

Short circuit ratio0.48

Field current4040A

Class & Type of insulation.MICALASTIC(Similar to Class F)

No. of terminals brought out...six (6)

Excitation System

For Stage I:In 200 MW turbo- generator, static excitation system is used. This excitation

system consists of an excitation transformer. This is a step down

transformer. The input to this transformer is taken directly from the

generator bus. From the excitation transformer the output goes to a thyristor

bridge which acts as full- converter and rectifies ac to dc. The thyristor

bridge gives a controlled dc output. The output of the rectifier bridge then

energizes the rotor of the synchronous generator. This output of the rectifier

bridge is fed to the rotor of the generator with the help of slip- rings and

brushes.

For Stage II:In 500MW turbo-generator, brushless excitation system is used. Brushless

exciter consists of a three-phase permanent magnet pilot exciter, whose

output is rectified and controlled by the thyristor voltage regulator to provide

a variable d.c. current for the revolving armature of the main exciter. The

three-phase current is induced in the rotor of the main exciter and is rectified

by the rotating diodes and fed to the field winding of the generator rotor.

Since the rotating rectifier bridge is mounted on the rotor, slip rings are not


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required and the output of the rectifier is directly connected to the field

winding through generator rotor shaft. A common shaft carries the rectifier

wheels, the rotor of the main exciter and permanent magnet rotor of the pilotexciter. The main exciter is of 6-pole revolving armature type. The three

phase pilot exciter is of 16-pole revolving field type.

De-excitation of the machine is effected by driving the thyristor to inverter

mode of operation causing the thyristor to supply maximum reverse voltage

to the field winding of the main exciter. Approximately 0.5 seconds after the

de-excitation command is received two field suppression contactors connect

field suppression resistors in parallel to the main exciter field winding and

following this a trip command is transmitted to the field circuit breaker via

its trip coil. In the event of failure of electronic de-excitation throughinverter operation, de-excitation is effected with a delay of 0.5 seconds by

the field suppression resistors.

Hydrogen Cooling SystemThe rotor winding is cooled by hydrogen flowing through the radial

ventilating ducts. It is designed for hydrogen pressure upto 3kg/sq. cm

gauge. Hydrogen is cooled by the gas coolers mounted on the stator body.

The hydrogen cooler water is cooled by water heat exchanger situated

outside the machine. The purity of hydrogen permitted is 97-99%. Hydrogenis preferred to air as the cooling media because of its lower density and

better thermal properties. While filling the generator for the very first time

with hydrogen, air inside it is purged by CO 2 and CO 2 is purged by

hydrogen. It is done in order to have safe filling of hydrogen. The hydrogen

inside the generator is maintained dry by continuously circulating the gas

through suitable hydrogen dryer.

Temperature LimitsThe class B type insulation is provided on the generator windings. RTDs

have been embedded in the windings for measurement of temperature.

Winding and core temperature recorders have been set for tripping 105C

for maximum temperature of stator winding. Rotor winding temperature is

recorded by a special recorder, which functions on the principle of rotor

winding resistance variation with temperature.

Generator Sealing Oil System


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To prevent the leakage of hydrogen, used for cooling in the generator, along

the generator shaft a seal oil system is applied. Shaft seals operate with flow

of oil under pressure. A pressure regulating valve maintains a constantdifferential pressure of seal oil over hydrogen pressure in the generator.

Vacuum treated oil is fed to the center of the seal ring assembly from the

seal oil supply unit. From here the oil flows in both directions between the

rings and the shaft, and thus a film is established in the constricted area,

which prevents the leakage of hydrogen. The main seal oil pump is driven

by a 440V ac motor. A dc motor supplied from the station battery drives an

emergency oil pump, which starts automatically when seal oil pressure drops

or ac motor trips due to any reason.

Generator Stator Water Cooling SystemA closed loop stator water cooling system is used to maintain a constant rate

of flow of demineralised cooling water to the stator winding at requisite

temperature. The stator water cooling system consists of two 100% primary

water to water heat exchanger, two 100% duty ac motor driven

demineralised water pumps, two 100% water filters, one 100% magnetic

filter, an expansion tank, specific heat measuring instruments etc. suitable

resistance temperature detectors are provided for measuring the temperature

of stator water at the inlet and outlet of stator winding.

Generator Main Bus:Generator main bus connections consist of natural air-cooled continuous

enclosure type isolated phase buses. No power circuit breakers are

interposed between the generator and the main generating transformers.

However, disconnecting links are provided for isolating purposes. The bus

duct enclosure is made of aluminium alloy sheet. Sealed openings are

provided in the bus-duct-run near the insulators for inspection and

maintenance. There is a main bus duct which is circular with diameterapproximately 1000mm where as the tap-off duct is circular of diameter

approximately 680mm.continuous current carrying capacity of main bus on

nominal voltage of 15.75KV is 10000A. Temperature rise of conductors and

for the enclosure (over the ambient of 50C) is 20C. The generator main

bus has the three isolated phase buses connected in star connection. The

neutral of the main bus is grounded through a Neutral Grounding

Transformer (NGT) i.e. a common duct comes out from where the three


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isolated phase buses are joined at a common point and goes to the primary of

the NGT.

Generator Transformer

For Stage I:

For each unit in stage I one 250MVA, 15.75/ 400KV three phase outdoor

transformer has been installed in the transformer yard. It is connected to the

generator through isolated bus ducts. The LV winding is delta-connected and

the HV winding is star-connected. The LV winding is delta-connected sothat if by chance there is a grounding fault in the generator then that fault

current will not pass on to the transmission line further as it will keep

circulating in the delta circuit itself. The HV side is star-connected because

the phase voltage in case of star-connection is 1/ 3 times the line voltage

and as the bus system used consists of isolated phase buses it is more

economical to use star-connection as the for lower voltage lesser insulation

will be required. Oil forced and water forced (OFWF) cooling is provided to

get continuous nominal rating of the transformer. It is equipped with all


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standard measuring and controlling fittings and accessories like Buccholz

relay, on-load tap changer, oil temperature indicator etc. deluge system is

also provided around the transformer for fire protection.The nameplate specifications of generator transformers in stage I are as

follows:

Generator transformer # 1 to 5:MakeBHEL

Manufacturing year.1981

Type of coolingOFWF

Rating..250MVA

Temperature rise- Oil.40CWater.60C

KV at no-load- HV400

LV15.75

Phase- HV3

LV3

Frequency.50Hz

Vector GroupYnd11

% Impedence...14%

Amperes- HV360.9

LV9184.9

Insulation level- HV1425KVP

LV95KVP

Core & Winding weight..140550 kg

Weight of oil49430 kg

Total weight.237400 kg

Quantity of oil..56820 liters

For Stage II:

The dual purpose of these transformers are to step up the output of 500MWgenerators from generation voltage of 21 KV to 400KV voltage for power

distribution and if required shall be back charged from 400KV side and used

to step down for feeding loads through unit auxiliary transformers.

These transformers are installed in the transformer yard adjacent to the

powerhouse building. The LV winding/ HV winding are delta/ star

connected. The neutral terminal is solidly grounded. The vector group of

these transformers when connected in a bank of three single- phase


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transformers is YNd11. These transformers are connected to respective

generators through isolated bus ducts. No power circuit breakers or power

switches are connected between generator and generator transformer.However, disconnecting links are provided at generating end for isolation

purpose. These transformers are equipped with independent oil forced and

water forced cooling system.

Generator transformer # 6 & 7:MakeBHEL


Type of coolingOFWF

Rating..200MVATemperature rise- Oil.50C

Water.60C

KV at no-load- HV400/ 3

LV21

Phase- HV1

LV1

Frequency.50Hz

Vector GroupYNd11

% Impedence...14%

Amperes- HV866.0

LV9523.8

Insulation level- HV1050KVP

LV125KVP

Core & Winding weight..1230- 50 kg




400 KV SWITCHYARD AT SSTPS

Switchyard is located 350 meters south of main powerhouse

building. 400kV switchyard is having two numbers of double main

and transfer bus system. Approximately 2000MW of SSTPS power


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is transmitted through 400kV switchyard. It is consisting of 23

bays, which includes generator and interconnecting transformer

(ICT) bays. 400kV is designed to limit the switching surge overvoltages to 2.5 P.U. and sustain temporary over voltage to 1.5 P.U.

The symmetrical fault current is 40kA (rms). The basic insulation

level (B.I.L.) is 1425kV. The switching surge is 1050kV. Each bus

comprises of three phase strung buses with four sub-conductors per

phase. ACSR MOOSE conductors are used for stringing on the

gantries of the switchyard. It is tied up with double tension string

assembly in twin/quadraple bundles with 450mm sub-conductor

spacing. For connecting the breaker with isolators 4 IPS

aluminium tubular buses in each bay are used. For intermediate

supports, bus post insulators are provided. One double main

transfer bus system having main buses 1 and 2 and transfer bus no.

1 caters for Bay no. 1 to Bay no. 12. Similarly, second double main

transfer bus system having main bus no. 3 and 4 and transfer bus

no. 2 caters for Bay no. 14 to Bay no. 23. Bay no. 13 interconnects


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400kV main bus 1 to 3 and 2 to 4. There is no interconnection

between transfer buses 1 and 2.

Bay-wise description of various feeders is as follows: -

1. 400KV Lucknow Line + 63MVAR Reactor2. 200MW 15.75KV Generator-53. 400KV Allahabad Line-2 + 80MVAR Reactor4. 200MW 15.75KV Generator-45. 400KV Bus Coupler-16. 200MW 15.75KV Generator-37. 400KV Anpara Line8. 200MW 15.75KV Generator-29. 400KV Allahabad Line-1 + 80MVAR Reactor10. 200MW 15.75KV Generator-111. 400KV Transfer Bus Coupler -112. 400KV Side of 100MVA 400/132KV ICT-113. 400KVBus Section 1&214. 400KV Side of 100MVA 400/132KV ICT-215. 400KV Vindhyachal-216. 400KV Transfer Bus Coupler-217. 400KV Vindhyachal Line-I18. 400KV Bus Coupler-219. 500MW 21KV Generator-620. 400KV Rihand Line-221. 500MW 21KV Generator-722. 400 KV Kanpur line23. 400 KV Rihand-I

The bay width is 27.0m. Height of the gantry structure is 13.7m

and intermediate gantry structure is 20.7m. Minimum ground

clearance is 7.1m. Earthing mat is laid of 40mm diameter MS

rounds throughout the switchyard and equipments grounding are

done by 7512mm strips. Generator bays are connected to

generator transformer secondary by overhead stringing.


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In SSTPS, transfer bus coupler scheme is applied. This scheme is

applied to transfer the load on one breaker to another breaker for

maintenance of a breaker. Suppose if a generating unit is supplyingpower to main bus 1. Now the breaker of the bay of this generating

unit has to be repaired then it is not a practical and economic

solution to trip the unit for this purpose. Therefore a parallel path is

created for the flow of power through the transfer bus using the

transfer bus coupler bay breaker to the main bus 1. For this first the

isolator in the generator bay connecting the feeder to the transfer

bus is closed. Then, in the TBC the breaker and associated

isolators to the main bus 1 are closed. After this the TBC baybreaker is closed and this creates a parallel path for the power.

Now the circuit breaker, which is to be repaired, of the generator

bay is opened and then the associated isolators are also opened.

The various equipments used in 400KV switchyard are as follows:ISOLATOR:An isolator is a switch, which can make or break an electric circuit

when the circuit is to be switched on no-load. Isolators cannotoperate unless the breaker is open. Bus 1 and 2 isolators cannot be

closed simultaneously. No isolator can operate when

corresponding earth switch is on.

There are two types of isolators used in the switchyard, namely the

sequential isolator and the pantograph isolator. The sequential

isolator is a two-post type in which the moving contact moves

through 90 on its axis. The pantograph isolator has two moving

contact arms designed in scissor-like fashion, which move throughonly 20 on its axis.

Circuit Breaker:A circuit breaker is a switch, which can make or break the circuit

on load and even on faults. It is heavy-duty equipment mainly


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utilized for protection of various circuits and operation at load. It is

installed accompanied by two isolators.

The various types of circuit breakers used in the switchyard are:

1.Bulk oil circuit breaker2.Minimum oil circuit breaker3.Air blast circuit breaker4.Sulphur hexa-flouride circuit breaker

These circuit breakers have been classified on the basis of their

quenching mechanism. The various operating mechanisms used for

these circuit breakers are spring operation, solenoid operation andpressure or pneumatic operation.

Earth Switches:These are devices which are normally used to earth a particular

system to avoid accident, which may happen due to induction on

account of live adjoining circuit. These switches do not handle any


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appreciable current at all. These are simple mechanically operated

switches.

Lightening Arresters:Lightening arresters are equipments which are connected at the

transformer terminals and the incoming terminals of the line for

protection against lightening or any surges developing in the

system. In this plant, valve type lightening arresters are used. Such

LAs consist of nonlinear resistors in series with spark- gaps. The

spark- gap assembly acts as a fast switch, which gets ionized

(conducting) at specified voltage. The entire assembly is placed inporcelain housing, properly sealed to keep out dust and moisture.

Wave Traps:Wave traps are parallel resonant circuits having negligible

impedance to power frequency currents but having very high

impedance to carrier frequency currents. They are used to keep

carrier signals in the desired channel so as to avoid interference

with or from adjacent carrier current channels and also to avoidloss of carrier current signal in the adjoining power circuits.

Current Transformers:A current transformer is a step down transformer which produces a

replica of the high current flowing in the circuit for measurement

purposes. It is intended to operate normally with rated current of

the network flowing through the primary winding which is inserted

in series in the network. The secondary winding of the CT isconnected to measuring instruments and relays supplying a current

which is proportional to and in phase with the current circulating in

the primary except for the difference due to current error and phase

displacement inherent in the design of the CT.


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Potential Transformer:Potential transformers step down the system voltages to

sufficiently low for indication of the system voltage conditions,

metering of the supply of energy, relaying and synchronizing. In

400 KV switchyard capacitance voltage transformer is used. A set

of CVT has been provided on each incoming/ outgoing line.

Shunt Reactors:Shunt reactors are static capacitors, which are connected in parallel

in the system, which produce reactive power in the power system.

In long lines a shunt reactor is connected for reduction of line

current, increase in voltage level at the load, reduction in system

losses, increase in power factor of a source current and reduction in

loading on source generators and circuits. They draw almost a

fixed amount of leading current which is superimposed on the load

current. This reduces the reactive component of the load current,

thereby improving the power factor.

CONTROL AND INSTRUMENTATION

The control and instrumentation systems installed in the plant are installed to

provide a comprehensive intelligence feedback on the important parameters

viz. temperature, pressure, level and flow. These systems are mostly based

on state of art microprocessor technology. They monitor the following

systems: -

SG C&I Systems:1. Furnace safeguard supervisory system for purging, automatic firing,

flame monitoring, sequential start- up and shut down of mills, etc.2. Secondary air damper control system3. Auxiliary PRDS control system4. Soot blower control system5. Coal feeder controls6. Furnace temperature probes

TG C&I Systems:1. Electro- hydraulic governing control system


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2. Automatic turbine run up system3. HP- LP bypass control system4. Turbine stress control system5. Automatic turbine testing system6. Turbine protection system7. Generator auxiliaries control system

Steam & Water Analysis System:This system does line analysis of various parameters like conductivity,

pH, dissolved oxygen, residual hydrazine, silica, sodium, phosphates,

chlorides, etc. at all critical points in condensate, feed water and steam

cycle.

The C&I systems employ the Distributed Control Monitoring & Information

System (DDCMIS) and Computerized Data Acquisition System. The

DDCMIS employs state of art microprocessors and is based on latest proven

technology. It performs the functions of sequencing and modulating

controls, plant start up/ shut down, in all regimes of plant operation

including emergency conditions. The main purpose of DAS is to acquire

sensor data and to produce useful output information for plant operators in

the form of displays and hard copies. This system combines special

hardware and software to facilitate interfacing between plant and operator.In addition, it also performs plant performance calculations and process

monitoring.

AUXILIARY POWER DISTRIBUTION SYSTEM

The auxiliary power distribution system distributes electrical power

requirement to various loads, control circuits and other instrumentation

circuits. The total load on auxiliaries in a power station is approximately 7%

to 9% of the plant capacity or the actual power generated. This system is

broadly divided into:-

1. Unit Auxiliary Power Distribution SystemUnit auxiliaries are those which are directly associated with the

generating unit such as ID and FD fans, boiler feed pumps, coal mills,

mill fans, circulating water pumps etc. The interruption of supply for the

auxiliary motors connected on the unit bus should not be there. For

supplying power to these unit auxiliaries the generator is connected to


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generator transformer through isolated phase bus duct and also through

two nos. of unit auxiliary transformers which step down the voltage to

6.6 KV. The UATs are connected to the unit 6.6 KV bus system by 2500A, 6.6 KV bus ducts. Each transformer is connected to unit buses A & B.

Medium voltage MOCB switchgear is used for feeding power to motors

rated above 200 KW. Facility is provided to transfer unit load to station

in the event of tripping of unit through changeover system.

Unit Auxiliary Transformer # 1 to 5:MakeKA CKBRIDGE HEWITTIC AND

EASUN LTD.


Type of coolingONAN (75%) ONAF(100%)Rating (KVA).. 12000 16000

Temperature rise- Oil.40C

Water.50C

KV at no-load- HV15.75

LV6.9

Phase- HV3

LV3

Frequency.50Hz

Vector GroupDYn11Amperes- HV 439.8 586.53

LV 1004.1 1338.8

Insulation level- HV125 KVP

LV60 KV P

Core & Winding weight..19200 kg




Unit Auxiliary Transformer # 6 to 7:MakeNGEF


Type of coolingONAN (75%) ONAF(100%)

Rating (KVA).. 17500 25000

Temperature rise- Oil.50C

Water.55C

KV at no-load- HV21


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LV6.9

Phase- HV3

LV3Frequency.50Hz

Vector GroupDYn1

Amperes- HV 481.13 687.32

LV 1664.3 2091.9

Insulation level- HV125 KVP

LV60 KVP

Core & Winding weight..21.6 T

Weight of oil7.3 T

Total weight.42.2 TQuantity of oil..8296 liters

2. Station Auxiliary Power Distribution SystemStation auxiliaries are those which are required for general station

services such as coal and ash handling system, lighting system, water

purifying system etc. interruption of supply for the auxiliary motors for

the station bus for a short duration can be tolerated. There are four station

transformers in the plant. These transformers are supplied from the 132

KV yard. These transformers step down the voltage to 6.6 KV. The

station transformers are resistance grounded.

WATER TREATMENT PLANT

Water treatment plant is to produce such a quality of feed water from which

there should not be any scale formation causing resistance to heat transfer

and thus failure of tubes, no corrosion and no priming or foaming problems.

This helps in giving trouble free, uninterrupted supply of clean steam. In this

plant, raw water is fed from the Rihand reservoir, which consists of ionic

and non-ionic, dissolved and undissolved solids and gaseous impurities. The

process of removing is show in the flow diagram: -


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Fig: -Block Diagram of water treatment Plant

Pre-Treatment Plant

This plant has a capacity to produce 600cu. M/hr. of clarified water to meetthe requirement of the DM plant. The various processes involved in the

pretreatment of water are:

ChlorinationChlorine is dosed in raw water inlet to aerator and further in clarified

water tank in order to remove bacteria and other microorganisms. It is

also effective in oxidation of Fe, Mn and H2S, removal of taste and

odour producing compounds and oxidation of organic compounds byforming chloroderivatives of these compounds.

AerationBy aeration the water absorbs oxygen from the atmosphere, which helps

in oxidation of organic matter present in water. The iron dissolved in

water is precipitated as Fe2O

3.

Coagulation


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After aeration, the water flows to the flash mixture where lime and alum

are dozed by the pumps and then flows through a RCC channel by

gravity. The added chemicals are thoroughly mixed with the raw waterwith the help of a stainless steel paddle fitted in the path. Chemical

reaction takes place as under:

Al2(SO

4)

3. 18H

2O + 3Ca(OH)

23CaSO

4+ 2Al(OH)

3

+ 18H2O

Flocculation & ClarificationThe water is subjected to slow spiral motion and fine precipitates

agglomerate to look distinctly as flocks. The clear water enters throughthe bottom opening. The scrapper attached to the rotating bridge scraps

the settled sludge. The clear water overflows from the top of rotating

bridge. The clear water overflow from the top of clarifier and led to

clarified water storage tank.

FiltrationThe clarified water is passed through four pressure filters in which graded

anthracite coal is filled up. During this process suspended impurity and

turbidity is filtered effectively. Now the water is passed through active

carbon filter to remove residual chlorine and oil impurities. Then it is fed to

ion-exchanger for removing mineral salts. In the cation exchanger cations

such as Ca, Mg and Na react with strong cation exchange resin and stay with

the reacted resin. Similar action takes place for removal of anions in the

anion exchanger. In the end a mixed bed exchanger is kept which helps in

removal of any left over anions or cations.

CIRCULATING WATER SYSTEM

Condenser Cooling Water System

The CW system provides for pond cooling with Rihand Reservoir as the heat

sink. Vertical wet pit type CW pumps draw water from the Rihand Reservoir

through the approach canal and feed to the condensers. Hot water from the

condensers is discharged back to the reservoir by means of discharge

channel, which is common for stage I and stage II of the project. CW supply

from CW pump house to the condensers and CW discharge from the

condensers upto the discharge channel is through concrete ducts of


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horseshoe shape. Round the year there is a large variation in the water level

of Rihand Reservoir. Minimum water level at the intake sump is 254 m and

the maximum level is 271 m with operating floor level of the pump housebeing at 278.5 m total depth of the sump is 31 m. therefore there is large

variation in the static lift of the CW pumps ranging from 7 m to 24 m. In

SSTPS, the operating scheme used to overcome this problem is by varying

the nos. of CW pumps in operation.

In stage I, total 13 nos. of pumps have been installed while 10 pumps are

required. Requirement of cooling water of each unit is 27000 m 3/hr. The

rated capacity of each pump is 15000 m 3/hr with a total head of 31.5 m.

These pumps are designed for continuous operation with cooling water of

maximum temperature of 36C.

In stage II, 3 nos. of CW pumps have been installed for each 500MW unit.

The rated capacity of each pump is 27000 m 3/hr at 31.5 m head. The

operating speed is 375 rpm and the driver is a 3MW, 6.6KV, 16- pole, 50 Hz

induction motor. In case of low water level, three pumps feed to one unit and

in case of higher water levels two CW pumps are sufficient for each unit.

For intermediate water levels five pumps are operated for both the units and

the interconnecting butterfly valves are kept open.

Ahead of the CW pumps single flow type traveling water screens have beenprovided with a clear opening size of 9.5 mm square which prevent the

debris from entering into the CW system.

Equipment Cooling SystemThe equipment cooling system has been provided to remove the waste heat

rejected from the various plant equipments and transfer it to the

environment. The system is divided into two basic sub-systems:

a) Primary circuit using DM water employed to pick up the heat load fromvarious auxiliary coolers and rejects the same to the plate type heat

exchangers (PHE).

b) Secondary circuit using raw water employed to pick up the heat loadfrom PHEs and reject the same to main circulating water discharge seal

pit in transformer yard.

The ECW system is capable of operating continuously during all modes of

plant operation. The ECW system meets the requirements of auxiliary

coolers other than the main condensers. The following auxiliary coolers are

cooled by primary water:


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1. SG Package Coal mill lubricating oil coolers, regenerative air pre-heaters - guide

bearing and support bearing oil coolers, water cooled access door infurnace hopper zones, lubricating oil coolers for FD/ ID/ PA fans and

motors, coolers for ID fan hydraulic couplings, sample coolers, ID fan

motors stator coolers, air heaters fire se, coal mill journal hydraulic

system cooler, boiler circulation pumps.

2. TG Package Turbine lubricating oil coolers, turbine control fluid coolers, generator

hydrogen coolers, exciter coolers, generator seal oil coolers hydrogen

and airside, primary water coolers.

3.BFP Package Booster pump coolers, working oil coolers and lubricating oil coolersfor MDBFP, BFP oil coolers, BFP motor coolers.

4. CEP Package Motor and thrust bearing coolers

5. Oil coolers for generator transformers6. Auxiliary coolers for air compressors7. Primary sample coolers in SWAS panel room in control tower.

The ECW heat exchangers are of plate type located at ground floor of TG

hall and sized to provide 38C (max.) DM water at design flow condition.

The pH of DM water in the closed loop is maintained around 9.5 by dosing

sodium hydroxide. The sodium hydroxide solution is prepared in NaOH

solution preparation tank and fed to the suction of DMCW pumps through

2100% chemical dosing pumps.

ASH HANDLING SYSTEM

The ash handling system is continuous hydro sluicing type. It envisagescontinuous removal of bottom ash and fly ash in slurry form from the

different zones of bottom ash and fly ash collections in the steam generating

units. The bottom ash slurry is led to a bottom ash slurry sump at the boiler

bottom from where it is transferred by means of vertical slurry pumps to the

main fly ash slurry trench in electrostatic precipitator (E.P.) area. The fly ash

slurry flows through gravity channels and aided by high pressure jetting

water is led to the slurry sump in the main ash slurry pump house. The

combined bottom ash and fly ash slurry from the main slurry sump is


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pumped to the disposal area by means of slurry pumps and disposal lines.

The HP and LP water required for slurry formation and transportation is

supplied by HP and LP pumps installed in ash water pump house.

The entire ash handling system has been designed for removing and flushing

the bottom ash and fly ash from both the units at the following rates:

For Stage I:

a) Fly ash 162 tonnes/hr (for phase I)

108 tonnes/hr (for phase II)

b) Bottom ash 36 tonnes/hr (for phase I)

24 tonnes/hr (for phase II)

For Stage II:

a) Fly ash 320 tonnes/hrb) Bottom ash 72 tonnes/hr.The ash slurry disposal system has been designed to pump the ash slurry

continuously from the slurry pump to the disposal area through pipelines at a

rate of 700 m 3/hr for each unit of stage I and 1500m 3/hr for each unit of

stage II.

Bottom Ash Removal SystemThe bottom ash resulting from the combustion of coal in the boiler falls into

the ash hopper provided under the furnace bottom. Each hopper is divided

into two sections and each section is provided with adequately sized opening

with gates. The ash is spray- quenched in these hoppers and gets discharged

into the water impounded slag baths provided under each section. Each slag

bath is provided with a continuously moving scraper feeder for transferring

the wet slag ash to the respective clinker grinder. The crushed ash through

clinker grinder gets discharged into the slopping ash trenches provided

beneath them and from there aided by high pressure water jets, the slurry is

led to the bottom ash slurry sump provided adjacent to the boiler bottom.

From the sump the slurry is transported to the main ash slurry trench in E.P.

area by bottom ash slurry pumps for its further disposal to dump area by

means of slurry disposal pumps located in main ash slurry pump house.

Fly Ash Removal SystemFly ash removal system envisages removal of ash from each of the

electrostatic precipitators, economiser, air preheater and stack hoppers

continuously through suitable vertical pipe connections. Flushing


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equipments are provided below them. The slurry from the economiser and

air preheater flushing equipments is conveyed to the bottom ash slurry sump

from where it is pumped along with bottom ash to the main ash slurry trenchin E.P. area.

The fly ash slurry from ESP and stack gets discharged into the sloping ash

channel provided beneath them. The slurry aided by high pressure water jets

flows down the sluice channel to the slurry sump in ash slurry pump house

for its further disposal to dump area by means of slurry pumps.

Ash DykeThe ash dyke is provided for the disposal of fly ash and bottom ash in the

form of slurry. Fly ash and bottom ash are collected in the slurry form in the

sump of the ash slurry pump house. From there it is discharged through

pipes into the ash dyke for the settlement of ash in the dyke. The ash free

water is discharged into the Rihand Reservoir.

There are three main ash slurry sumps, one common for units 1, 2 & 3,

second common for units 4 & 5 and third common for 6 & 7. Low pressure

water is used for thorough mixing and high pressure water is used for

sluicing. Each ash slurry sump is located in an ash slurry pump house. Eachpump house has six vertical pumps for continuously conveying the ash

slurry from the sump to the ash dyke.

HYDROGEN GENERATION PLANT

Hydrogen gas is used for generator cooling. So supply of pure hydrogen in

the power station is essential for generator filling and maintaining of

hydrogen gas pressure inside the generator casing.

Hydrogen is prepared by electrolysis of pure demineralised water. When dc

current is passed through water it decomposes the water into two elements,

one volume of oxygen and two volumes of hydrogen. Pure distilled water is

a bad conductor of electricity but if acid, alkali or salt is added it becomes a

good conductor. To make economical use of electrolysis of water, a solution

termed as electrolyte has be used which is prepared by adding NaOH or

KOH with pure water. When current is passed through the electrolyte,


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hydrogen is given off at negative electrode, while oxygen is evolved at the

positive electrode.

A.C. power at 400/440 V, 3 phase, is changed to dc power in a transformer

and rectifier arrangement. Dc output of the plant is controlled by means of a

regulator. Dc from the terminals of the rectifier is supplied to the cells

through busbars. Gas production is directly proportional to dc current

passing through the solution of caustic potash and DM water.

DM water of high purity is collected in a storage tank from where it is fed by

gravity to the cell bank for make up. An automatic float valve is mounted in

gas washing tank to provide a continuous supply of water in proportion to

usage. The gases, after leaving the cells, pass upwardly to the collectionheaders and then through a water seal to atmosphere or to the gasholder as

the case may be.

Cooling water is supplied to the water seal, which regulates the pressure

head against which the cells operate and also prevents any backward flow

from the gasholder when the plant is not in operation. Valve is provided in

between the gas washing tank and gasholder for directing the flow to

atmosphere when desired.

Hydrogen gas flows from the gas washing tank to a low pressure wet seal

gasholder. From the gasholder it flows to a compressor, which compresses it

to rated pressure. After the compressor it flows through carbon filter and

through a silica gel dryer. The dry hydrogen is then stored in storage

cylinders from where it goes to the power station for use. Hydrogen gas is

normally sent to HP compressors from the gasholder where it is compressed

to a rated pressure. From the HP compressors, hydrogen flows through an

after cooler, which has moisture separator columns, and then to a point

filling station where it is filled in portable cylinders.

Oxygen produced in the process is let off to atmosphere.


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BIBLIOGRAPHYBIBLIOGRAPHYBIBLIOGRAPHYBIBLIOGRAPHY

The information, facts and figures presented in the project have

been collected from various sources. To mention a few,

information have been collected from websites like

www.google.comand www.wikipedia.org. Various documentaries

have also been referred to for collecting valuable information. We

have also referred to reference books. To mention a few, we

referred electrical technology by B. L. Theraja and A.K. Theraja

and Power systems by V.K. Mehta.


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