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KTPS-B STATION

REPORT FOR A MINI PROJECT ON

OVER VIEW OF THERMAL

POWER STATION

SUBMITTED BY:

NAME ROLL NO.

BEZAWADA CHAKRADHAR 09232

P.VAMSHI KRISHNA 09236

R.ADITYA ANVESH 09257

B.NAGESWARA RAO O8258

National Institute Of Technology-Warangal

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ABSTRACT

Concern over the electrical demand in the country,

Kothagudem Thermal Power Station was established

extending the wide electrical network in the state of Andhra

Pradesh.

We are going through a detailed study of various steps

involved in generation of power in a thermal power plant.

Ideas of Efficient combustion of coal, efficient utilization of

heat energy through a Regenerative system, Water Cycle,

Steam Cycle, Working of Turbine, Self utilization of Power,

Transferring the generated power to the Grid, Handling of

Ash are mainly focused.

New ideas for Handling of Ash, efficient pulverizing of coal,

better water treatment, effect of pressure of steam on turbine,

developing required pressure to attain required RPM and

construction of boiler that suits for requirement of KTPS are

studied and analyzed.

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ACKNOWLEDGEMENT

WE SINCERELY THANK MR.LAKSHMAN

(ADE/EM/KTPS-B STATION) SIR FOR GUIDING US

TO COMPLETE THE PLANT OVER VIEW.

WE SINCERELY THANK MR.VEDA KUMAR

(ADE/EM/KTPS-B STATION) SIR FOR HIS

CONCEPTUAL GUIDENCE IN UNDERSTANDING THE

MECHAISM OF POWER STATION

WE SINCERELY THANK MR.VENU

(ADE/EM/KTPS-B STATION) SIR FOR HIS CO-

OPERATION TO STUDT THE POWER PLANT.

WE SINCERELY THANK MR.T.SATYANARAYANA

(DE/EM/KTPS-B STATION) SIR FOR PERMITTING

US TO DEAL WITH THIS MINI PROJECT.

WE HEARTFULLY THANK MR.RAMBABU

(SWITCH YARD) SIR & MR.RAMAKRISHNA

(LIFT MAINTENANCE) SIR FOR THEIR SUPPORT

AND GUIDENCE IN STUDYING THE POWER STATION

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CONTENTS

Topic P.No.

All Thermal Power Stations in India 6

Introduction to APGENCO 7

Introduction to KTPS 9

In to the working of the plant 13

Coal Handling Plant 16

Coal Milling Plant 18

Water Handling System 26

Working of Thermal Power Plant 27

Working of the Boiler 29

Steam with the Turbine 31

Cooling Towers 37

Boiler Feed Pump 40

Regenerative System 42

Handling of Ash 43

Generator 46

Transformers 55

KTPS Switch Yard 58

MCR & UCB 71

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A broad view of Thermal Power Plants in INDIA

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INTRODUCTION TO APGENCO

Andhra Pradesh Power Generation Corporation Limited (APGENCO) is the electricity generation company of the Government of Andhra Pradesh found in the year 1998 as a part of the network of APSEB (Andhra Pradesh State Electricity Board) in India. It has an installed capacity of 7048.4 MW which makes it the third largest power generation company in India.

Andhra Pradesh Power Generation Corporation Limited is one of the pivotal organizations of Andhra Pradesh, engaged in the business of Power generation. Apart from operation & Maintenance of the power plants it has undertaken the execution of the ongoing & new power projects scheduled under capacity addition programme and is taking up renovation & modernization works of the old power stations. APGENCO came into existence on 28.12.1998 and commenced operations from 01.02.1999. This was a sequel to Governments reforms in Power Sector to unbundle the activities relating to Generation, Transmission and Distribution of Power. All the Generating Stations owned by erstwhile APSEB were transferred to the control of APGENCO. The installed capacity of APGENCO as on September 30, 2010 is 8135.9 MW comprising 4382.50 MW Thermal, 3751.40 MW Hydro and 2 MW Wind power stations, and contributes about half the total Energy Requirement of Andhra Pradesh. APGENCO is third largest power generating utility in the Country next to NTPC and Maharashtra. It's installed Hydro capacity of 3703.4 MW is the second highest among the Country.

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Statistical Information Regarding Different Thermal Power Plants Operating

Under APGENCO

Power Station

Operator Location District Unit Wise Capacity

Installed Capacity

Plant Coordinates

Ramagundam B Thermal Power Station

APGENCO Ramagundam Karimnagar 1 x 62.5 62.5 18°43′31″N79°30′47″E

Kothagudem Thermal Power Station

APGENCO Paloncha Khammam 4 x 60, 4 x 120

720 17°37′18″N80°41′15″E

Kothagudem Thermal Power Station V Stage

APGENCO Paloncha Khammam 2 x 250 500 17°37′24″N80°42′06″E

Dr Narla Tatarao TPS

APGENCO Ibrahimpatnam Krishna 6 x 210, 1 x 500

1760 16°35′58″N80°32′12″E

Rayalaseema Thermal Power Station

APGENCO Cuddapah YSR 4 x 210 840 14°42′14″N78°27′29″E

Kakatiya Thermal Power Station

APGENCO Chelpur Warangal 1 x 500 500 18°23′02″N79°49′42″E

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INTRODUCTION TO KTPS

With a concern of increase in demand for electrical energy

in INDIA, to meet the required demand for energy in Andhra

Pradesh Kothagudem Thermal Power Station (KTPS) was

established extending wide electrical network in the state in

the year 1966.

Under Japanese collaboration KTPS was established in

1966 with an initial capacity of 120 MW (2 X 60 MW) and then

in the 1967 it was extended to 240 MW (4 X 60 MW) which is

popularly known as KTPS-A station. The highlight point is, this

is one of the oldest power plants in the world under Japanese

collaboration. It is not exaggerating to quote that engineers

from Japan still attend here for case study and update their

report for their future investments. Station A consists of four

units, popularly called as 1st, 2nd, 3rdand 4th units of KTPS with

each unit capable of generating a power of 60 MW. In due

course of time the total A-station got Indianized.

In the view of progress later in the year 1974 KTPS-B

station came in to existence with a initial capacity of 220 MW

(2 X 110MW). But later these units were upgraded to 120 MW

each with total production increased to 240 MW (2 X 120MW)

in B-station itself. The two units in this B-station are popularly

called as 5th and 6th units.

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Successfully running on the track of development KTPS-C

station came on to the screen in the year 1977 with a capacity

of 110 MW (1 X 110 MW) and with in no time production was

extended to 220 MW (2 X110 MW) in the year 1978. Later the

total production of C-station was successfully upgraded to 240

MW (2 X 120 MW). These two units are called 7th and 8th units

of KTPS.

In due course of development a new stage of power plant

has been constructed with larger capacity turbines capable of

producing 250 MW in the year 1998. Two such turbines are

being installed in this station popularly called as KTPS-5th stage.

Total production capacity of 5th stage is 500 MW (2 X 250 MW).

Now recently the proposal of KTPS-6th stage is successful.

The estimated capacity is 500 MW (1 X 500 MW). This was

thought to be synchronized with the grid by March 31st, 2011.

This observed to be successfully running.

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A Tabulated view of Production in different units of KTPS

Stage Unit

Number

Installed Capacity

(MW)

Date of Commissioning

Status

Station A 1 60 04-07-1966 Running

Station A 2 60 27-11-1966 Running

Station A 3 60 27-05-1967 Running

Station A 4 60 08-07-1967 Running

Station B 5 110 13-08-1974 Uprated to 120 MW

Station B 6 110 19-12-1974 Uprated to 120 MW

Station C 7 110 10-03-1977 Uprated to 120MW

Station C 8 110 10-01-1978 Uprated to 120 MW

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Stage Unit

Number

Installed Capacity

(MW)

Date of Commissioning

Status

5th stage 9 250 27-03-1997 Running

5th stage 10 250 28-02-1998 Running

6th stage 11 500 2011 Running

The station has been the recipient of many prestigious

awards from various organizations including Meritorious

awards instituted by the government of India. The station has

received Meritorious productivity awards for nine times and

Incentive award for eight times.

For the 5ht stage the station has received the meritorious

productivity award for four consecutive years (1999-2000,

2000-01, 2001-02, 2002-03) by the government of India. The

station has received Meritorious productivity awards for nine

times and Incentive award for eight times.

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IN TO THE WORKING OF PLANT

BASIC PRINCIPLE INVOLVED IN WORKING:

The basic principle involved is Faraday’s law of electro-

magnetic induction i.e. “whenever a conductor cuts a

magnetic flux emf is induced across its ends”.

BASIC IDEA OF OPERATION:

The very first thing we need to provide is a conductor

cutting magnetic flux. So this can be done in two basic ways i.e.

either the conductor can be moved in the magnetic field or the

field can be varied according to the required emf that is to be

generated. The process we follow here is we rotate the rotor of

a generator in the magnetic field and emf is generator at the

stator and this generated emf is further utilized according to

the purpose.

To meet the purpose of rotating the rotor of a generator,

the rotating shaft is in turn connected to a turbine which is

made to rotate at a rated speed by an external energy source.

So we need an energy source to rotate the turbine. To rotate

the turbine energy must be transferred from a medium to the

turbine so that energy from the external source is converted to

rotational energy of turbine.

In general to rotate an object which is mounted we need

to apply some torque. To produce torque we need to apply

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force in the tangential direction. For the purpose of application

of force we chose steam as a medium of transfer. For hydel

plants water is directly allowed from a very great height to

collide with the turbine blades with a great force.

In the same way we need to send the steam with a greater

force in turn with a greater pressure to make the turbine

rotate. The basic physics involved in this is the internal energy

and enthalpy of the steam gets converted to mechanical energy

that rotates the turbine.

Our target is to produce steam at a very high pressure.

Pressure of the steam can be increased by various auxiliaries

through different mechanisms. So basically we need to produce

steam. For the production of steam water is to be heated to

high temperatures with the help of available fuel. Combustion

of fuel is done and evolved heat is utilized for production of

steam.

Total idea is to be implemented in a highly efficient way to

balance the finance and economy. Environmental protection

should also be the point of concern because burning of fuel

may evolve gases which are responsible for harmful effects that

distract our ambience.

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BASIC REQUIREMENTS:

Fuel

Water

Heating system

Steam circuit

Regenerating system

Steam turbine

Generator

Transformer

NOTE: ANY INFORMATION DISCUSSED FROM NOW ONWARDS

IS MAINLY CONSERNED TO KTPS-‘B’ STATION

FUEL:

The available fuel for us is COAL. Coal is transferred in

lump sum from nearby coal mines popularly called as

SINGERENI COLLARIES through wagons.

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COAL HANDLING PLANT (CHP)

Daily 3 racks of coal will be transferred to the plant. Each

rack consists of 56 wagons each carrying coal around 60 tonnes.

E-grade and F-grade coal is being transferred to plant

whose calorific value varies in between 2700-3600 K.Cal/Kg.

WAGON TIPPLER:

The coal received from the collieries, is more than 100 rail

wagons a day, is unloaded mechanically by two ways, 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 55-60 tonnes capacity in an hour.

CONVEYOR BELT:

It is a normal rubber belt carrying the coal from one place

to the other in the course of processing. The belt runs at a

speed of 2.5 m/s with the help of a induction motor in

connection with a speed reducing gear.

MAGNETIC PULLEYS:

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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, 3phase, 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. CRUSHER HOUSE: The unloaded coal is dragged on to mesh with slots of size “300 X 300” mm2 with the help of dozers. The filtered coal through mesh is carried through conveyor belts to hoppers from where coal is sent to crushers.

Two nos. hammer type coal crushers are provided, which can crush coal to a size of “25 X 25” mm2. The crushed coal is then supplied to Boiler Raw Coal Bunkers (RC 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.

NOTE: To be on safe side coal required for one month will be

kept in reserve condition in the yard, the storage yard and the

raw coal is required for one day is kept in reserve condition in

the RC bunkers.

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COAL MILLING PLANT

Raw Coal Bunkers (RC Bunkers)

Raw Coal Chain Feeders

Drum Mills or Coal Mills

Classifier

Cyclone Separator

Vapour Fan

Pulverized Cola Bunkers (PC Bunkers)

RAW COAL BUNKER: Each of three raw coal bunkers is fabricated from the sheet metal and is well stiffened all around. The storage capacity of each raw coal bunker is about 500 tones. There are four outlet gates with each bunker. The gates are electrically operated from site. In case of failure of the electric motors the gate can be hand operated from site. At a time only one gate opening is suffices but should be changed so that there is no pilling within the bunker.

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RAW COAL CHAIN FEEDER:

The raw coal chain feeder transports coal from raw coal

bunker to the inlet chute leading to the pulverized/coal mills. There is a double link chain of high tensile strength steel, which moves on wheels and sweeps the raw coal falling over the top of the raw coal chute of the mill. The height of the coal bed in the chain feeder can be adjusted manually by means of lever operated damper.

The maximum and minimum heights of the coal bed are 200mm and 120mm respectively. The signaling equipment indicates the absence of coal flow in the feeder, which is annunciated in the unit control board (U.C.B.). The main shaft on the driving end is connected to the driving unit, consisting of variator, a gear box and a motor all mounted as a single unit. The chain wheel on the driving end shaft is provided with a shear pin, which will shear off and disconnect the driving mechanism if there is any overload on the feeder.

The speed of the chain feeder is regulated automatically/remotely by actuating the control spindle of the variator through a servomotor. A pump for circulating the oil in

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the gear box of variator is an integral part of variator driven by a separator motor. Some of the technical data about the raw coal chain feeder is given here:- 1. Output of the chain feeder 10-45 tonnes/hr. 2. Speed variations 0.0503-0.151m/sec. 3. Main motor 7.5kW, 415V, 50Hz. 4. Oil pump motor 0.05kW, 220V 5. Operating motor of each gate 3HP, 415V and 50Hz.

We can change the quantity of coal which is fed to mill in two ways. -> By changing the speed of chain -> By changing the depth of coal in chain Speed of chain can be changed by adding a gear system to motor. We connect the gear system with motor with a pin called shear pin. This prevents the overloading of motor because when the coal quantity of coal on chain is greater than its capacity then the pin will break and prevent the pin from overloading. Speed of Raw Coal chain is 2” to 6”/sec. DRUM MILL:

Each mill consists of single compartment drum, bearings driving motor, coal inlet and discharge piping, ball change and lubricating equipment for mill bearings. Mill drum is fabricated from thick steel plates and is supported on to the anti-friction bearings. The mill is driven by an electric motor of capacity 630kW, 990 rpm, and 6.6kV through a reduction gear, which reduces the speed to 17.5 rpm.

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Picture of Ball Mill or Coal Mill:

The ball charge for the mill consists of the three different

sizes of forged steel balls detailed as below. The capacity of each mill is 36.7 T/hr. 1. 40mm diameter 22500 kg 2. 50mm diameter 20000kg 3. 60mm diameter 10000kg 4. Total Ball Charge 52500kg

During operation only 60mm diameter balls are added is

approx. 500 kg per week and the guiding factor is the amperage of the coal mill, normally it should be 66-ampere approx. at full

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load and when it falls below the above value ball charging of the mill is carried out. Lubricating system consists of the oil tank, gear pump, oil cooler and base frame to mount all these equipments.

Gear pump is driven by an electric motor of rating 1 H.P., 415 V, 1440 rpm. Suction side of the gear pump is connected to the tube oil tank and the delivery side is connected to inlet of the oil cooler and after cooling oil goes to the bearings. The oil from the bearings is cooled to the required temperature in the cooler by the means of plant bearing cooler water.

CLASSIFIER: The classifier is fabricated from the steel plates. It is the

equipment that separates fine pulverized coal from the coarser pieces. The pulverized coal along with the carrying as well as drying medium (flue gas) strikes the impact plate in the classifier and the coarser pieces get separated due to the change in the direction of flow and go back to mill. The stream then passes to the outlet branch of the classifier through an adjustable telescopic tube. At the outlet adjustable vanes are provided to change the size of coal when required. CYCLONE SEPARATOR:

The centrifugal type cyclone separator consists of two cyclones made up of welded sheets. It is equipment in the milling plant, which serves for separating the pulverized coal from the vapours i.e. carrying medium. The pulverized coal gets stored in the pulverized coal bunkers and vapours go to suction of vapour fan. At the bottom of the cyclone separator a rotary

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valve (Trinket) is provided to transport coal from cyclone separator to P.C. bunker on the worm conveyor as the case may be. VAPOUR FAN: Pulverized coal from the cyclone separator is carried to the PC bunkers by the vapour fan. This is just a suction fan for carrying light coal particles. For this purpose a 3 Phase induction motor is used. Voltage applied 6.6 KV Rating 400 KW RPM 990 Current 44 amps PULVERIZED COAL BUNKERS (PC BUNKERS): After complete pulverizing of coal in to fine powder and separation of fine coal particles from coarse particles the final fine powder is sucked through vapour fan in to storage hoppers called PC Bunkers. From here coal is directly sent to furnace for combustion. NOTE: The actual need for pulverization of coal before sending it to furnace is combustion of powdered coal is more efficient than normal sized coal particles. So finer the particle is higher is the efficiency of combustion. So more is the combustion less is the evolution of poisonous gases like CO and less is the pollution and more is the energy collected.

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PRIMARY AIR FAN:

The pulverized coal can directly be supplied to the boiler

furnace for combustion with the help of primary air fan

popularly called as “PA FAN”. The temperature of the coal is

maintained with the help of hot air stream supplied by the PA

fan.

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MOTOR 3 Phase Induction Motor

400 KW, 900 RPM, 6.6 KV, 44 amps

Capacity 33 m3/ s

Suction Double

WATER:

Next basic requirement water is available in lump sum

from “KINNERASAANI RESERVOIR”. Kinnerasani is a tributary

for river Godavari. A reservoir was constructed across this

tributary from where water flows by gravity(due to difference

of height in ground level) to KTPS reservoirs.

During the construction of A-Station reservoir with

capacity of 120 Lakhs Gallons was constructed. Later for B-

station 2 reservoirs each with a capacity of 60 Lakhs Gallons

was constructed.

Even from here water flows to clarifier naturally by gravity.

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WATER HANDLING SYSTERM

CLARIFIER:

Water from reservoir is directly filled in to ALUM

TANKS in which raw water is treated with ALUM for

precipitating mud. Chlorination of water is also done here to

remove different bacteria and algae present in the water. With

the help of Central Fraculator mud in the water gets separated

along with some amount of water and remaining clarified water

is pumped towards De-Mineralizing plant through Booster

Pumps.

DE-MINERALIZING PLANT:

Here water is sent through a series of sand filters to

remove any impurities present. Now-a-days carbon filters are

also used for this purpose. In the next step water is sent

through a CATIONIC EXCHANGE RESIN for the removal of any

metal cat ions. Now water is passed through DE-GASIFIER TANK

to remove the trace of CO2 whose output is connected to a tank

containing ANIONIC EXCHANGE RESIN for removal of non

metallic anions. As a final step this water is sent through

another tank containing both the resins called mixed beds.

From here water is sent to units for supplying to the boiler to

produce steam.

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NOTE: THE MAIN REASON FOR DEMINERALIZING WATER IS TO

PREVENT THE DAMAGE IF PIPE LINES CARRYING STEAM, TO

PREVENT THE DAMAGE OF BOILER DRUM AND TO PREVENT

THE DAMAGE OF TURBINE BLADES.BECAUSE OF PRESENCE OF

SALTS IN WATER SCALES ARE FORMED ON THE PIPE SURFACE

AND DRUM SURFACE.THIS MAY DAMAGE PIPE AND

DRUM.EVEN THE BLADES OF THE TURBINE ARE ALSO

EFFECTED BY THIS.SO TO PREVENT DAMAGE AND CORROSION

WATER NEED TO BE DEMINERALIZED.

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WORKING OF THE BOILER

Generating and maintaining fire:

Generation of fire is done with the help of oil and lighters.

Oil is sprayed from four corners of the furnace with the help of

oil guns and lighters at four ends of the furnace release sparks.

This sparks make the oil to catch fire. Now coal is carried from

PC Bunkers with the help of PA Fan. Cola is kept hot i.e. at a

temperature around 70oC for effective burning of coal. This

temperature is maintained with the help of hot air from PA fans

and secondary air.

Coal is released from four diagonal corners of the boiler

continuously to maintain the temperature through PC injectors.

In case of drop of temperature at any corner more amount of

coal is dropped at that end through adjustment in the valve

system. The temperature in the furnace will be around 1500oC.

For the coal to be burnt effectively oxygen should be

supplied uninterruptedly. For this FD fan is engaged.

FORCED DRAUGHT FAN:

This fan sucks air from the open atmosphere and supplies

it to the boiler furnace for effective combustion of coal. As the

open air contains 21% of oxygen this fan helps for combustion.

Capacity 62 m3/sec

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16V control

3 Phase induction motor

400 KW, 6.6 KV, 990 REM and 44 amps.

Generating and processing steam:

Water from DM plant is fed to the pipes that are in contact

with the walls of the furnace. Heat evolved from the burning of

coal in the furnace is utilized to convert water in to steam.

Steam obtained here will be at a temperature of 350o C and at a

pressure around 140 Kg/cm2. This is fed to boiler DRUM where

an interface separates water and steam. The upper part of the

drum is filled with steam which is wet in nature and the down

part with water from Boiler Feed Pump (BFP).

But this steam will be wet in nature because of presence

of moisture in the steam. This is called wet steam. So, to make

it dry this steam is passed through SUPER HEATER COILS to

produce dry steam. Temperature of dry steam is around 540o C

and a pressure of 140 Kg/cm2.

Water from the drum is sent around the furnace and is

converted to steam (wet) and brought back to boiler drum.

Again from here it is sent to superheated coils to produce dry

steam and the process continues.

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STEAM WITH THE TURBINE

To generate EMF the rotor of the generator need to be rotated

which in turn is operated by a shaft which is rotated with the

help of three turbines.

HIGH PREESSURE TURBINE (HP TURBINE)

INTERMEDIATE /MEDIUM PRESSURE TURBINE (IP

TURBINE)

LOW PRESSURE TURBINE

Each turbine has its own operating temperature and pressure.

Steam from the super heater coils is fed directly to the HP

turbine at a temperature of 540o C and a pressure around

140Kg/cm2. The enthalpy of the steam gets converted to

mechanical energy which makes the turbine to rotate. From the

law of thermodynamics “a perpetual motion machine of second

kind doesn’t exist”, heat energy cannot be completely

converted to work. So some amount of energy still remains in

the steam.

To re-utilize this energy this steam is made to interact with

another turbine called Intermediate/Medium Pressure

Turbine. Before making them to interact the outlet steam from

the HP turbine is sent back to furnace and reheated through

reheater coils .This is a part of regenerative system for efficient

utilization of heat energy. Steam from reheater coils is fed to IP

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Turbine. Again from second law of thermodynamics some

amount of energy still remains in the steam.

The outlet steam from the IP Turbine is directly fed to LP

Turbine where maximum amount of energy is expected to be

utilized. The outlet steam of the LP Turbine contains very low

amount of energy as it is already used for 3 times with 3

different turbines this cannot be used for regeneration. So this

steam is allowed for condensation.

Turbine Lubricating Oil System:

Turbine lubricating-oil system seeks to provide proper

lubrication of turbo-generator bearings and operation of

barring gear.

The recommended working medium for governing and

lubrication system of the turbine is Turbine oil-14 of INDIAN OIL

COMPANY.

OIL SPECIFICATION:

1. Specific Gravity at 50”C 0.852

2. Kinematic Viscosity at 50”C 28 centistokes

3. Neutralization number 0.2

4. Flash Point 201”C(min)

5. Pour Point -6.6”C(max)

6. Ash % by Weight 0.01%

7. Mechanical Impurities Nil

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The Turbine Lubricating oil system mainly consists of

Main Oil Pump (MOP)

Starting Oil Pump (SOP)

AC standby Oil Pumps

emergency DC oil pump

Jacking oil pump (JOP) (1 per UNIT) .

Main Oil Pump is used for the Lubrication system. It is

coupled with turbine rotor through a gear coupling and is used

when the turbine is running at normal speed (3000 rpm) or

greater than 2800 rpm.

Starting oil pump is a multi-stage centrifugal pump driven

by A.C electric motor. It is provided for meeting the

requirement of oil of the turbo-set during starting or stopping

and also as standby to maintain centrifugal oil pump.

Standby oil pump is a centrifugal pump by an A.C electric

motor, this runs for 10 min in the beginning to remove air from

the governing system and fill the oil system with the oil.

Emergency Oil Pump is a centrifugal pump driven by D.C

electric motor. This automatically cuts in whenever there is a

failure of A.C supply at POWER STATION and or the pressure in

lubrication system falls.

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Jacking Oil Pump enable 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.

Oil Coolers:

The oil of the lubrication and governing system is cooled in

the oil coolers. Circulating water is used as the cooling medium

for these oil coolers.

5 oil coolers are available at the plant, out of which 4 are

for continuous operation and one remains as standby.

Steam turbine as prime mover:

The steam turbine offers many advantages over other

prime movers, both thermodynamically and mechanically.

From a thermodynamic point of view the main advantage

of steam turbine over say a reciprocating steam engine is that

in the turbine the steam can be expanded down to a lower back

pressure there by making available a greater heat drop, If a

reciprocating steam engine is to expand the steam down to a

back pressure of the order of an inch or two of mercury and the

low pressure cylinders would have to be a very large to deal

with large volume of steam resulting from these pressures.

From a mechanical point of view the turbine is ideal

because the propelling force is applied directly to the rotating

element of the machine and has not as in the reciprocating

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engine to be transmitted to a system of connecting links which

are necessary to transform a reciprocating motion into a rotary

motion.

If the load on the turbine is kept constant that are

developed at the coupling is also constant. A generator at a

steady load offers a constant torque. Therefore a turbine is

suitable for driving a generator, particularly as they are both

high speed machines.

A further advantage of the turbine is the absence of

internal lubrication. This means that the exhaust steam is not

contaminated with oil vapour and can be condensed and fed

back to the boilers without passing through filters.

Steam cycle:

The steam plant uses a dual (vapour + liquid) phase cycle.

It is a closed cycle to enable the working fluid (water) to be

used again and again. The cycle used is “RANKING CYCLE”

modified to include super heating of steam, regenerative feed

water heating and reheating of steam.

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CONDENSOR:

The outlet steam of the LP Turbine is sent to condenser

where steam is passed through pipe lines and cool water is

allowed to be in contact with these pipes. Because of the heat

exchange between steam and cool water steam gets converted

to water and stored in HOT WELL.

HOT WELL:

Water from the condenser pipes are pumped in to a

sump called HOT WELL. Water in this well is around 50o C. From

here water will be sent to cooling towers for cooling.

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COOLING TOWERS:

From hot well water is sent to cooling towers for the

purpose of cooling. Here water will be taken to an elevation of

10-12 mts. and allowed to fall freely. Water is allowed to fall at

different points. At each and every falling point sprinkling

mechanism is arranged. At every small depth a grill

arrangement is fixed to collide with the water droplets falling

freely. A scale like arrangement is fixed at every small depth.

This is done because to make the water droplets to collide with

these grills and to decrease the size of the water droplets.

So smaller is the water droplet faster will be the heat

exchange with the medium in which it is present. As heat is

being evolved from every droplet of water some droplets of

38

water may absorb the heat. This makes some water droplets

increase their temperature rather than cooling. The heat

exchange takes place in such a way that the temperature

crosses its boiling point an even latent heat is also absorbed

converting water droplets to vapour.

This vapour is allowed in to the atmosphere at greater

heights. So in cooling towers water gets cooled and gets

converted to vapour too. To allow vapour in to free atmosphere

at greater heights vapour needs to be carried to greater

heights. Rather than spending energy to carry the steam to

greater heights some civil engineering techniques are applied in

construction of cooling tower.

The construction of cooling tower involves basic laws of

fluid mechanics. The walls are hyperbolic in shape following

SIPHON mechanism. These are also called HYPERBOLIC

NATURAL DRAUGHT COOLING TOWERS. Once vapour is left to

the atmosphere forcibly in the beginning the process continues

by itself until the vapour terminates which doesn’t happen

because vapour continuously emits.

This is called Natural Draught. The other mechanism that

can be followed is Forced Draught & Induced Draught in which

fans are arranged and vapour is sent out forcibly.

NOTE: KEEP IT IN MIND THAT WATER COOLED IN TOWERS IS

DEMINERALIZED WATER.SO THIS WATER SHOULD NOT BE

39

LEFT FREE OR WASTED.THIS WATER CAN BE USED AGAIN TO

PRODUCE STEAM AND RUN THE TURBINES.AS PROCESS OF

DEMINERALIZING WATER IS VERY COSTLY, THIS WATE IS USED

AGAIN.

Water from cooling tower is sent to condensate sump.

From here water is heated through a series a heaters called LP

heaters and HP heaters.

LP Heater is a heater which heats the water with the help of a

tapping from the steam line going to the LP Turbine. A series of

such LP Heaters are employed to increase the temperature. The

out let of LP Heater is fed to the Deaerator.

DEAERATOR:

Deaerators are mechanical devices that remove dissolved

gases from boiler feed water. Deaeration protects the steam

system from the effects of corrosive gases. It accomplishes this

by reducing the concentration of dissolved oxygen and carbon

dioxide to a level where corrosion is minimized. A dissolved

oxygen level of 5 parts per billion (ppb) or lower is needed to

prevent corrosion in most high-pressure (>200 pounds per

square inch) boilers. While oxygen concentrations of up to 43

ppb may be tolerated in low-pressure boilers, equipment life is

extended at little or no cost by limiting the oxygen

concentration to 5 ppb. Dissolved carbon dioxide is essentially

completely removed by the Deaerator.

40

Deaerators use steam to heat the water to the full saturation

temperature corresponding to the steam pressure in the

Deaerator and to scrub out and carry away dissolved gases.

The outlet of the Deaerator is fed to the BOILER FEED PUMP

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 120 MW turbo set 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.

41

Type 200 KHI Delivery capacity 445 t/hr. Feed water temperature 158°C Speed 4500 rpm Pressure at suction 8.30 kg/cm2 Stuffing box mechanical seal Lubrication of pump by oil under pressure Motor bearing supplied by hydraulic

coupling Consumption of cooling water 230 L/min. The outlet of BFP is around 140 Kg/cm2. This is fed to HP Heaters. HP Heater is a heater that heats the outlet of BFP with the help of a tapping from the steam line of HP Turbine. A series of such HP Heaters are employed and then finally its outlet is fed to ECONOMISER in the furnace. ECONOMISER: It is a part of regenerative system for efficient utilization of heat energy from the furnace. Steam from HP Heater is fed to the economiser tubes. Here steam gets heated up to 350o C. the outlet of economiser is fed to the boiler drum. In the boiler drum steam and water gets separated and steam is sent to super heater coils and same process repeats as explained earlier.

42

REGENERATIVE SYSTEM: It is a designed loop for effective utilization of energy to increase the efficiency of the process. In general furnace is meant to produce the steam from water. But total energy evolved from combustion of coal is excessive for this. So this heat energy from the furnace is repeatedly utilized wherever necessary through

SUPER HEATER COILS

REHEATER COILS

ECONOMISER

43

HANDLING OF ASH

After combustion of coal ash will be remained in the furnace. Handling of ash is the major problem for any thermal power plant. In the bygone ash was dumped at a far place, because of this a lot of land is being wasted.

In general two types of ashes need to be handled.

Bottom Ash

Fly Ash Bottom Ash is collected at the bottom of the furnace in the hoppers provided. The ash deposited at the bottom of the furnace is collected in a water impounded hopper where a continuous flow of water is maintained to limit the temperature of ash inside the hopper. The bottom ash cleaning is done in every cycle of 8 hours. The bottom ash system is local manually operated. On opening of feed gate ash is allowed to discharge into a double roll Linder grinder where it is grounded to smaller size, which can be transported through the pipe line below the linker grinder there is a venturi which sucks the ground ash the vacuum created at the venturi throat by the flow of high pressure water tapped. Dawn stream of the discharge of the ash water pumps. The pressure recovered at the end of venturi is adequate to convey the slurry to disposal area. Fly Ash is collected with the help of a fan called induced draught fan.

44

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. This fan sucks the ash [particles from the mouth of the furnace to the chimney passing through the electrostatic precipitators. 3 phase induction motor 800 KW ELECTROSTATIC PRECIPITATORS: Particles travelling due to the effect of ID fan are made to

enter in to ESP’s. In this section those particles are made to

travel in between two plates with a potential difference of

40KV (DC Voltage is applied). The positive and negative ions

formed by the burning of coal are precipitated here. At regular

intervals these plates were hit by the hammers so that

precipitated ions get separated from the plates in the form of

powder. This powder is the byproduct and can be sold. This is

used by the cement industries.

45

The un-precipitated particles are carried away by the ID

fan in to the chimney.

CHIMNEY:

Finally, the un-precipitated particles are left to the

atmosphere from a greater height, nearly twice the height of

cooling tower. The construction of chimney is also done in the

same way as cooling towers. Walls are hyperbolic in nature

following the SIPHON mechanism with a natural draught outlet.

46

GENERATING POWER:

We have gone through the process how steam is

generated and interacted with turbine. As we have discussed

the 3 turbines rotate a single shaft at a rated speed of 3000

RPM. This shaft is in turn connected to a TURBO GENERATOR

which can generate an EMF of 11 KV.

Generator Components :

Rotor :

The electric rotor is the most difficult part of the generator

to design. It revolves at a speed of 3,000 rpm hence high care

has to be taken during its design. The passage of current

through the windings generates heat but high temperature

results in insulation problems. To keep the temp down rotor

cross section has to be reduced but that results in mechanical

weakness of the rotor. Hence it has to be designed such that it

carries more current at the same time it is mechanically strong.

This can be achieved with good design and great care in

construction.

The rotor is a cast steel ingot, and it is further forged and

machined. A hole is bored through the centre of the rotor

axially from one end to other for inspection. Slots are then

machined for windings and ventilation.

47

Rotor Windings:

Silver bearings copper is used for the winding with mica as

the insulation between conductors. The designs of large rotor

windings incorporate combination of hollow conductors with

slots or holes arranged for circulation of cooling gas. To prevent

the windings from flying off away at high speeds due to

centrifugal force wedges are provided. The two ends of

windings are connected to slip rings.

Rotor Balancing:

To provide mechanical balance for the rotor , so that it

rotates without vibrations arrangements have been made in all

designs to fix adjustable balance weights around the

circumference at each end.

Stator:

Stator comprises of an inner frame and an outer frame.

The outer frame is a rigid fabricated structure of welded steel

plates, within this shell is a fixed cage of grinder built circular

and axial ribs. The hydrogen for cooling of stator flows through

these ribs.

The inner cage is usually fixed in to the yoke by an

arrangement of springs to dampen the double frequency

vibrations present in 2 pole generators.

48

Stator Windings:

Each Stator conductor must be capable of carrying the

rated current without overheating. The insulation must be

sufficient to prevent leakage currents flowing between the

phases to earth. On recent generators the windings are made

up from copper tubes instead of strips through which water is

circulated for cooling purposes. The water is fed to the

windings through plastic tubes.

EXCITATION SYSTEM:

The excitation system of a generator consists of :

The main exciter

The pilot and auxiliary exciters

The voltage control system

Development Of excitation system:

Initially the dc excitation system was being used. The

development of improved techniques resulted in the increased

capacity of generators which in turn raised demand of

excitation power. But it found that dc excitation could not meet

the demands of large capacity turbo-generators due to

following reasons.

High excitation currents at comparative low voltage were

required and these would entail a large number of brushes

49

operating on exciter commutator. This will create difficulties in

operation and will require extensive maintenance of

commutator and brush gear.

The other disadvantage of dc exciter is that commutator

may be satisfactory during steady state during load fluctuations

there is a risk of flash over at the commutator. The maximum

peripheral speed of commutator for proper operation should

not be more than 45 meters per second.

Reliability is one of the main requisites of excitation

system of the generator. This accelerated development of AC

excitation system, where AC generator along with rectifier

system is used for field excitation.

DC EXCITATION SYSTEM:

Direct current exciters are shut wound machines and

compounding can be included to improve response. The open-

circuit characteristics and basic diagram of a self excited

compound shut wound exciter are shown in the following

figure. It is important to note that the unstable voltage region

HB on open circuit characteristics of the exciter. Since OE is the

excitation current when voltage BE is across the shunt field

BE/OE is the value of the critical resistance of the circuit. The

line of this critical resistance coincides with slope of voltage

characteristic. Therefore, the voltage is indefinite and can vary

freely between the value due to exciter permanent magnetism,

50

and value B the voltage due to field current OE. Even small

temperature increases in the field winding will contribute to

voltage instability. A method of overcoming this effect is to

insert a saturation liner behind each pole piece. Because of

reduced magnetic section the liner is saturated much sooner

than the pole body, thereby

it

introducing the required non-linearity in the open-circuit

characteristic. One adverse effect of the saturation line

however, is to depress the ceiling voltage of the exciter.

51

Basic schematic diagram of DC excitation system

Exciter field windings can compromise two or three

separate windings. The main field winding are often duplicated

to provide parallel current paths to reduce contact wear and

field rheostat wear.

The provision of a negative field gives a negative bias in

the exciter by which response is improved when load is thrown

off. It also improves the lowering response of the exciter

system following as external fault clearance and reduces the

range of main exciter field current needed for a given change in

exciter voltage. But this negative field constitutes a constant

load on pilot exciter and necessitates a more powerful positive

main field than would be the case without negative bias. These

disadvantages are justified. However, on the ground of improve

52

exciter performance, it should be noted that negative excitation

like this cannot be achieved in present AC exciter systems.

AC excitation system:

The AC exciter for large units gained favor because it was

possible to use 2 or 4 pole revolving field type machines

possessing all the robustness associated with the generator.

Commutator and DC brush gear were eliminated giving place to

the simple rotor slip-rings and associated brush gear. A pilot

exciter is a necessary part of the ac exciter system. It is

common practice to have pilot exciter, itself an ac machine. The

pilot exciter can also be a permanent magnet generator. It must

operate over a wide range with ceiling valves considerably

greater than the rated full load valve. Furthermore the exciter

output must respond quickly to excitation changes at its own

rotor terminals. The excitation is controlled by the AVR. The

excitation for pilot exciter is obtained from a permanent

magnet of exciter where output is rectified. The pilot output,

which excites the field of AC main exciter, is controlled by

automatic voltage regulator. The rectified output of main

exciter then energies the rotor of the synchronous generator. In

main exciter the AC supply can be taken from the grid or

generator itself rectified and given to the generator field. This is

called Static Excitation.

53

Bsic schematic diagram of AC excitation system

Generator Cooling & Sealing System

The 120 MW Generator is provided with an efficient

cooling system to avoid excessive heating and consequent wear

and tear of its main components during operation.

Rotor Cooling System:

The rotor is cooled by means of gas pick up cooling. The H2

gas in the air gap is sucked through the scoops on the rotor

wedges and is directed to flow along the ventilating canals

milled on the sides of the rotor coil. Due to rotation of the

rotor, a +ve suction as well as discharge is created due to which

a certain quantity of gas flows and cools the rotor.

54

H2 Cooling System:

Hydrogen is used as cooling medium in large capacity

generator due to its high capacity of heat carrying and low

density. But in view of its forming an explosive mixture with

oxygen, proper sealing system has to be provided and see that

there is no escape of hydrogen from the generator. Mainly oil

sealing is used to seal hydrogen.

Stator Cooling System:

The stator winding is cooled by distillate which is fed from

one end of the machine by Teflon tube and flows through the

upper bar and returns back through the lower bar of another

slot. Turbo-generators require both water cooling arrangement

as well as hydrogen cooling steam .The cooling water is used

for cooling of stator winding , hence high quality water(de-

mineralized water) is used for its cooling.

Generator Sealing System:

Seals are employed to prevent leakage of hydrogen from

the stator at the point of rotor exit. A continuous film between

the rotor collar and the seal liner is maintained by means of the

oil at a pressure which is about to start above the casing

hydrogen gas pressure, which is regulated in relation to the

hydrogen pressure and provides a positive maintenance of the

oil film thickness.

55

This 11 KV voltage is stepped up or stepped down using

different type of transformers.

TRANSFORMERS:

Different types of transformers are used for stepping up and

stepping down the generated voltage either for supplying to

the grid or for self utilization.

GENERATOR TRANSFORMER

UNIT AUXILIARY TRANSFORMER

STATION TRANSFORMER

GENERATOR TRANSFORMER: (GT)

Generated 11 KV is stepped up to 220 KV using generator

transformers for transmitting to the grid through the switch

yard. The 11 KV voltage is stepped up for transmitting because

to reduce I2R losses. If voltage is maintained high then current

is maintained low since the produced power remains constant.

If current is low then I2 is low and loss of power is low.

The produced power is in AC 3 Phase, so we need 3 Phase

transformer to step up or step down.

56

3Phase 11 KV / 220 KV TRANSFORMER.

Manufacturer BHEL

UNIT AUXIALIARY TRANSFORMER: (UAT)

We have seen that many motors need to be run in the

plant such as ID, FD, PA fans etc. and for the internal needs of

the plant power is needed. So rather than collecting the power

from the grid 10% off the produced power is self utilized by the

57

plant. For this purpose produced 11KV is stepped down to 6.6

KV using UAT.

This 6.6 KV is fed to different motors as per requirement

and for remaining purposes this voltage is again stepped down

to required levels.

STATION TRANSFORMER: (ST)

This is also a step down transformer 220 KV / 6.6 KV. The

primary of the transformer is directly connected to the 220KV

bus from the grid through the switch yard and is stepped down

to 6.6 KV. This is a safety transformer i.e. keeping in the view

that if there is some problem with UAT’s and the system getting

failed by chance the required power is collected directly from

the grid and is stepped down for plant requirements so that

there is no obstacle for power production.

58

KTPS SWITCH YARD

INTRODUCTION:

An electrical substation is an assemblage of electrical

components including bus bars, isolators, circuit breakers,

transformers, lightning arresters, instrument transformers, etc.

Electric power between incoming and outgoing circuits, in

substation takes place through bus bars. We can say, the bus

bars are junction points capable of carrying huge power.

Bus bars are conducting bars to which a number of

incoming or outgoing circuits are connected. Electrical

components of each circuit are connected in a definite

sequence such that a circuit can be switched on/off during

normal operations. In KTPS O&M we are using Double Bus Bar

system with quadrantone ACSR conductor.

TASKS OF THE SWITHCH YARD :

a. Protection of transmission system (to isolate faulty

network from the healthy one)

b. Controlling the exchange of power (i.e. to control the

power transmission to load points as per requirements

and instructions of LDC.)

c. Maintain the system frequency within targeted limits.

(This can be done by raising/ lowering of generation or

load shedding.)

59

d. Determination of power transfer through transmission

lines.

e. Fault analysis and subsequent improvements.

f. Communication: data transfer via power line carrier for

the purpose of network monitoring, control and

protection.

Equipments in Switch Yard:

Insulators

Conductors & Accessories

Clamps & Connectors

Circuit Breakers

Isolators

Earth Switch

Instrument Transformers

Surge Arrestors

Wave Traps

Insulators:

60

The flexible ACSR conductors of transmission line and

substation bus bars are supported on string insulators. The rigid

tubular bus bars in SS are supported on Solid insulators/Post

insulators.

Conductors & Accessories:

Conductor consists of several strands (individual wires)

wound in layers spiraled along the length of conductor.

Consecutive layers are twisted spirally in opposite direction to

provide good interlayer grip and gives strength and flexibility to

the total conductor.

Electrical Grade Aluminum wires or Al alloy wires are used

for conductor for carrying current. In the core, Galvanized Steel

wires are used for reinforcement .The core gives high tensile

strength & conductor has low resistance.

Clamps & Connectors:

Tee-Connectors: For connecting ACSR conductor to ACSR tap

conductor (dropper)

Parallel-Grove Connectors (PG clamp): For connecting two

ACSR flexible conductors in parallel.

Fixed type bus post Clamps: For supporting tubular bus on post

insulators.

Pad Clamps: For Isolator to ACSR conductor connections

Spacers.

61

For twin conductor bundle.

For quadruple conductor bundle

Hardware for string insulator assembly.

62

CIRCUIT BREAKERS:

Circuit breakers are switching devices, design to close or

open contact members, thus closing or opening an electrical

circuit under normal or abnormal conditions.

Circuit breaker is automatic switching Device which can

carrying normal current & switching in & out

normal loads

Interrupt short circuiting currents.

can able to performer auto-reclose duty.

Classification of circuit breakers:

Based on LOCATION

Indoor

Outdoor.

Based on INTERUPTING MEDIUM

Air break Air Break Circuit Breaker (ACB)

Air blast Air Blast Circuit Breaker (ABCB)

Bulk oil Bulk Oil Circuit Breaker (BOCB)

Minimum oil Minimum Oil Circuit Breaker (MOCB)

SF6 gas insulated SF6 Circuit Breaker (GCB)

Vacuum Vacuum Circuit Breaker (VCB)

63

ISOLATORS:

In sub-stations it is often desired to disconnect a part of

the circuit for maintenance or repairs of conductors, clamps,

CBs etc. This is accomplished by an Isolator (Isolating

switch).Isolators are switches operated when the line in which

they are connected carry no current.

Isolator (disconnecting switch) operates under no load

condition. It does not have any specified current breaking

capacity or current making capacity. Isolator is not even used

for breaking load currents. In some cases isolators are used for

breaking charging current of transmission line.

Isolators used for power systems are generally 3-pole

isolator. The 3-pole isolator has three identical poles. Each pole

consists of two or three insulator posts mounted on a

fabricated support. The conducting parts are supported on the

insulator posts. The conducting parts consist of conducting

copper or aluminum rod, fixed and moving contacts. During the

opening operation the conducting rod swings apart and

isolation is obtained. The simultaneous operation of three poles

is obtained by mechanical inter locking of the three poles.

Further, for all three poles, there is a common operating

mechanism.

The operating mechanism is manual plus one of the following:

64

1. Electrical motor mechanism

2. Pneumatic mechanism

Further, the isolator can be provided with earthing switching

when required. The earthing switch consists of a conductor bar.

When the earthing switch is to be closed, these bars swing and

connect the contact on line unit of isolator to earth.

65

EARTHING SWITCH:

Earthing switch is connected between the line

conductor and earth. Normally it is open. When line is

disconnected, the earthing switch is closed so as to discharge

the voltage trapped on the line. Though the line is

disconnected, there is some voltage on the line to which the

capacitance between line and earth is charged. This voltage is

significant in high voltage system. Before proceeding, with the

maintenance work these voltages are discharged to earth by

closing the earth switch.

INSTRUMENT TRANSFORMERS:

CURRENT TRANSFORMERS:

Protective relays in a.c power system are connected in the

secondary circuit of the current transformers .

Current transformers are classified into two groups

1. Protective current transformers

2. Measuring current transformers

Ratio error and phase angle errors are the important

errors of these transformers .The ratio error is very important

in protective current transformers ,and phase angle error may

be less important .

66

Larger cores and air gaps are introduced in CT`S for fast

protective relays , in order to prevent saturation of current

transformer cores during sub-transient current.

DESCRIPTION OF CT`S:

The current transformer types IT 245 are out door, single

phase post type with oil impregnated paper insulation and

hermitically sealed enclosures.

The primary winding is of eyebolt design with capacitance

graded voltage insulation. Primary currents are more than one

value is obtained by providing either primary reconnection or

secondary tapping.

The core is made of high-grade electrical steel through

which the required numbers of secondary turns are wound

torridly. This assembly is located in the eye of the primary

winding. The active part is located inside tank. There is more

than one secondary, to achieve various functions like metering

or protection. A high voltage porcelain insulator serves as the

external insulation. One oil sight glass is provided and section

head contains the primary terminals.

A Nitrogen valve in the dome, Nitrogen gas which acts as a

cushion for expansion and contraction of oil.The transformer is

hermetically sealed to eliminate moisture absorption and oil

contamination.

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OPERATION:

CT`S whose primary windings have been energized

must not be open on the secondary side. The secondary

winding should either be short-circuited or closed by a load

corresponding to the rated burden indicated on the rating

plate.

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VOLTAGE TRANSFORMERS:

Voltage transformers are used for measurement and

protection. These are necessary for voltage directional,

distance protection. The primary of the voltage transformer is

connected directly to power circuit between phase and ground

depending upon rated voltage and application. The volt ampere

rating of voltage transformer is smaller.

There are two types of construction:

- Electromagnetic potential transformer, in which primary

and secondary are wound in magnetic cores like usual

transformer.

- Capacitor potential transformer, in which the primary

voltage is applied to a series capacitor group. The voltage

across one of the capacitor is taken to auxiliary voltage

transformer. The secondary of auxiliary voltage transformer is

taken for measurement or protection.

NOTE:CT’S AND PT’S ARE EXTERNALLY VISIVBLE WITH

COMBINATION OF DISC SHAPED STRUCTURES CALLED PETTI

COATS.THIS STRUCTURED IS PREFERRED TO ERADICATE THE

SHORT CIRCUITIN AND EARTHING DURING RAINING.WATER

FALLS ON THE DISC SHAPED STRUCTURE AND IS DEVIATED IN

ITS DIRECTION NOT FORMING A CONTINUOUS LINE OF WATER

69

DROPLETS WHICH CAUSES GROUNDING OR SHORT

CIRCUITING.

A View of a PT:

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Surge Arrestors:

Metal oxide surge arrester also known as zinc oxide surge

arresters are well accepted as voltage clippers for effective

protection against over voltages. Metal oxide surge arresters

protect the costly outdoor electrical equipment from over voltages

caused by atmospheric disturbances due to lightning and internal

disturbances due to switching surges. The assembly consists of

Metal Oxide elements with contact plates between discs and held

rigidly by a tie rod assembly. The striking aspect of this arrester is

its simplicity of construction.

Working: This zinc oxide acts as an insulator up to the voltage

of 220 KV and if voltage exceeds to a greater extent due to

lightening or internal disturbances breakdown of zinc oxide

occurs and charge is completely passed in the ground. High

frequency high voltage waves are discharged in to the ground.

WAVE TRAPS:

It is also called "Line trap". It is connected in series with

the power (transmission) line. It blocks the high frequency

carrier waves (24 kHz to 500 kHz) and let power waves (50 Hz -

60 Hz) to pass through. It is basically an inductor of rating in

milli Henry.

71

Main Control Room (MCR):

Each and every part of the switch yard can be operated

with computer based software technique from Main Control

Room. Any problem anywhere in the BUS, FEEDER, CB,

ISOLATER etc., can be found out without manual effort from

MCR.

Unit Control Board (UCB):

Each and every unit in the thermal power station can be

controlled and operated with computer based software

techniques from UCB. Any problem anywhere in the turbine,

BFP, Fans, bunkers, boilers etc., can be found at UCB without

any manual effort.