Gujarat State Electricity Corporation Limited

Gujarat State Electricity Corporation Limited

PREFACE

Knowledge is precious, but wisdom comes through experience”. A famous philosopher once quoted these wise words to make people understand the important of practical knowledge.

Theory of any subject is important but without practical knowledge it becomes of no importance, particularly for engineering student cannot be a perfect engineer or a professional without practice understanding of a field of study. Hence an in-plant vocational training provides a golden opportunity to interact with the working environment.

The principle of in- plant is to get familiar with the various equipment, unit operation, and unit processes used in the industries.

Its attractive feature is to learn about industrial management and marketing. Which are of equal to learn about industrial management and marketing trends which are of equal importance. In plant training is very much advantageous for the engineering students who have a wide idea about the theoretical concept of the various unit operations, unit process. This training helps in understanding the basic concept and other practical ideas involved in industries.

More than everything it strictly includes discipline, which is most important in industries as well as in practical life. Then we learn to live in industrial atmosphere.

My short Training to GSECL Gandhinagar gave me an opportunity to develop both these skills i.e.(practical knowledge & ability to develop principle), these training has only added to my technical knowledge, but also developed a new disciplined and enthusiastic spirit with me.

Apex Institute Of Engineering And Technology1


AKNOWLEDGEMENT

We take this opportunity to thank all the honourable member of management and administration for giving us this opportunity to gain the vast knowledge present within its giant promises.

We express our heartily gratitude towards Mr A.J. Tatu sir Who warmly welcomed us on the very first day and ensured us of all possible support from his side, along with his fellow officials, They kept their promise and helped us lot ways we needed them.

We specially thanks to Mr Ramanuj Sir, Mr Gupta sir for his guidance.

We thank all the officials’ engineers and technician together for all their supports which were useful and inevitable.

I am also grateful to Head of Electrical Department. Mr Aakash Sakhsena sir & Mr. Sunil S. Agarwal sir and all faculty member of Apex institute of engineering and technology, Jaipur.



INDEX

1- GENERAL2- INTRODUCTION3- DIAGRAM OF A TYPICAL COAL-FIRED THERMAL POWER STATION4- SCHEMATIC DIAGRAM OF THERMAL POWER PLANT5- CYCLES6- PROCESS DESCRIPTION

(6.1)- Boiler (6.2)- Super Heater (6.3)- Economizer (6.4)- Air Preheater (6.5)- Condenser (6.6)- Turbine (6.7)- Alternator (6.8)- Exciter (6.9)- Transformer

7- COAL HANDLING PLANT8- SWITCH YARD9- AUXILIARY SYSTEM10- CONTROL SYSTEM11- BIBLIOGRAPHY



GENERAL

Gujarat State Electricity Corporation Limited (GSECL) was incorporated in August 1993 and is registered under the Companies Act, 1956 with the objectives to initiate a process of restructuring of Power Sector and to mobilize resources from the market for adding to the generating capacity of the State and improving the quality and cost of existing generation. The Company was promoted by erstwhile Gujarat Electricity Board (GEB) as it’s wholly owned subsidiary in the context of liberalization and as a part of efforts towards restructuring of the Power Sector.

The Memorandum and Articles of Association of GSECL envisage a wide spectrum of activities to improve the electricity infrastructure of Gujarat. GSECL has initiated its activities in the field of Generation of Power. The Government of Gujarat (GoG) has also given to the GSECL the status of Independent Power Producer (IPP) with approval to undertake new power projects.

The Company commenced it’s commercial operation in the year 1998. However, the operations of GSECL were limited to Power Stations units Gandhinagar #5, Wanakbori #7, Utran GBPS & Dhuvaran CCPP till the complete unbundling of erstwhile GEB was undertaken, i.e. up to 31st March 2005.

As a part of the ongoing reforms process in the state power sector, in the year 2003, The Government of Gujarat under the provisions of Gujarat Electricity Industry (Re-Organization & Regulation) Act, 2003 framed the Gujarat Electricity Comprehensive Transfer Scheme, 2003 (the Transfer Scheme) vide Government Notification No: GHU-2003-58-GEB-3537–K dated the 24th October, 2003. The Government of Gujarat issued Notification No. GHU-2004–99-GEB-1104- 7318-K dated the 31st December 2004, notifying the Provisional Opening Balance Sheet as on 31st March 2004 of the Six Transferee Companies containing the value of assets and liabilities transferred from erstwhile Gujarat Electricity Board (GEB) to the Transferee Companies. Assets of the Board were disaggregated into six companies – One each in Generation and Transmission and Four in Distribution. As a part of the above exercise, all the generation plants of GEB have been transferred to GSECL, which was a company already, in existence since 1993.

Existing Power Plants

Sr. No.Name of Power Stations

No. of Units

Total MW/ Station

I. Thermal Power Stations

1. Gandhinagar Thermal Power Station

i. 2x120

ii. 3x210

870

2. Ukai Thermal Power Station

i. 2x120ii. 2x200iii. 1x210

850



3. Wanakbori Thermal Power Station

i. 7x210 1470

4. Sikka Thermal Power Station

2x120 240

II. Gas Based Power Stations

1. Dhuvaran GBCCPP Unt-I

i. 1x67.85

ii. 1x38.77

107

2. Dhuvaran GBCCPP Unt-II

i. 1x72.51

ii. 1x39.94

112.45

3. Utran Gas Based Power Station (STG)

I. 3x30

ii. 1x45

135

III. Lignite Power Station

1. Kutch Lignite Thermal Power Station

i. 2x70

ii. 1x75

215

IV. Hydro Power Stations

1. Ukai Hydro Power Station

i. 4x75 300

2. Kadana Hydro Power Station

i. 4x60 240

3. Ukai left Bank Canal Hydro Power Station

i. 2x2.5 5

4. Panam Canal Mini Hydro Power Station

i. 2x1 2

Total (I+II+III+IV) 4766



Power Projects Under Implementation

1. Kutch Lignite Thermal Power Station 1 x 75 75

2. Utran Gas Based Power Station 1 x 370 370

3. Sikka Coal based Power Satation 2 x 250 500

4 Ukai Coal based Power Station 1 x 500 500

Total 1445

SECTOR STRUCTURE

As a part of the reform process,the Government of Gujarat has unbundled the various functions of GEB. As a result of this unbundling,Gujarat State Electricity Corporation Limited (GSECL) has taken up the responsibility of electricity generation. Electricity Transmission has been entrusted to the already existing company - GETCO. Distribution network in the state has been split up among four distribution companies, which cater to the northern, central, southern, and western parts of the state respectively. All these companies have been structured as subsidiaries of a holding company, Gujarat Urja Vikas Nigam Limited (GUVNL). GUVNL is also the single bulk buyer in the state as well as the bulk supplier to distribution companies. It will also carry out the trading function in the state. The pictorial representation of the restructuring is as given below:



Commercial Arrangements

As per the new sector structure, GSECL has entered into a Power Purchase Agreement (PPA) for selling energy with GUVNL. The contractual / commercial arrangements post unbundling are represented diagrammatically below:

2 : Contractual Framework Post Unbundling



INTRODUCTION

GUJARAT ELECTRICITY BOARD

Installed capacity of various power station of Gujarat state as on 31-12-2000.

Sr no Name of the power station Installed/derated capacity A-GEB

1 DHUVARN TPS (4×63.5+2×140+2×27=588) 0588 MW2 UKAI TPS(2×120+2×200+1×210=850) 0850 MW3 WANAKBORI TPS (3×210+3×210=1260) 1260 MW4 GANDHINAGAR TPS(2×210+2×120=660) 0660 MW



5 SIKKA TPS (2×120=240) 0240 MW6 K.L. TPS (2×70+1×75=215) 0215 MW7 UTRAN TPS (OLD) (3×15) 0045/39 MW8 KADANA HEP (3×60=180) 0180 MW9 UKAI HEP (4×75=300 ) 0300 MW10 UKAI LBCH (2×2.5=5) 0005 MW11 UTRAN TPS (NEW) CCPP (3×30+1×45=135) 0135 MW 12 PANAM HYDRO PROJECT (2×1=2) 0002 MW

TOTAL (A) 4540/4534 MW

B-IPP1 GANDHINAGAR TPS (1×210) 0210 MW2 A.E CO. (4×15+2×30+3×110+2×32.5+35) 0550/510 MW3 G.I.P.C.L (3×32+49=145+169) 0555 MW4 ESSAR (300) 0300 MW5 GUJ. TORRENT ENERGY CO.(3×138=414) 0414 MW6 WANAKBORI -7 (1×210) 0210 MW

TOTAL (B) 2480/2440 MW

C- CENTRAL SECTOR NCP TARAPUR APS 190/160 MWNCP KAKARAPAR APS 0125 MWNTPC KORBA 0360 MWNTPC VINDYACHAL O230 MWNTPC KAWAS 0184 MWNTPC JHANOR 0234 MWTOTAL (C) 1323/1293 MW

Total installed capacity of Gujarat state A+B+C = 8343/8217 MW

GEB GANDHINGAR TPS:-

India relies heavily on Thermal Power Stations fueled by coal ,oil ,and natural gas to meet its electrical demand.Our country is a develoipng nation and electricity is directly related with our economic growth.

Gandhinagar thermal power station one of prestigious power stations of the Gujarat electricity board is situated at the right bank of river sabarmati , is mainly constructed to meet with the power need of north Gujarat and to improve the village condition of the grid. Gujarat Electricity Board (GEB) satisfies most of the power demand of whole gujarat state. TPS of Gandhinagar is one of the most prestigious power stations across the state situated at the bank or the river Sabarmati,with the capacity of 870 MW. It is mainly constructed to meet the power need of North Gujarat and to ameliorate voltage condition of grid system.

This power station has taken shape in three phases :

FIRST STAGE(unit 1&2)



It comprises of two units of 120 MW each for which construction work was started int the year 1974 and completed within record period of 3.5 years.

SECOND STAGE(unit 3&4)

It comprises of two units of 210 MW each for which construction work was started int the year 1990/91. Unit 3&4 has the advance features like protection and interlocking system for automatic sequential start up and shut down of important auxiliaries,also modern technical features like EAST (Electronic Automation of Steam Turbine) and ATRS (Automatic Turbine Run up System) and DAS (Data Acquisition System).

THIRD STAGE( unit 5)

This unit has installed capacity of 210 MW and was set up in the year 1997/98. This unit has latest technologies like DDS control with WSPOSE system(Distributed Digital Control with Work Station Base Plant Operator Environment System).

Important and notable point is that this plant is working at very good load factor and has also received many Awards for that.

First stage comprise of 2×120 MW units for which the construction work had started in the year 1974 and completed within a record period of 3 ½ years and that too by saving of rupees four crores from the estimated budget provision of rupees sixty crores . since than these two units of 120 MW each are running continuously without giving any major trouble . Similarly stage –II consisting of 2 units of 210 MW each have also added to the installed capacity of this TPS from the year 1990/91 and are running at full load without any problem .further one more unit No.5 of 210 mw capacity has been added to the installed capacity of Gandhinagar TPS to bring it to 870 MW .

SPECIAL LATEST TECHNOLOGY ADOPTED FOR UNIT NO 3,4AND 5

For providing uninterrupted power supply to the consumers and for doing so GEB has done in for the latest technology available . in Gandhinagar unit No. 3& 4 the advance features like protection and inter locks systems for automatic sequential start up and shut down of important auxillaries also,( Automatc turbine run up system have been incorporated).

Similarly for 210 mw Unit no.5 GEB has gone for some more lattest technology and have introduced first time DDS control with WSPOSE system (Distributed digital control with work station base plant operator environment system) .by this system GEB has embarked in complete plant automation of worlds largest technology . the automation system controls and monitors plant start up , operation as well as shut down . This system will than automatically and immediately respond without time delay to bring the plant or process into a safe operating state with respect to environment , process components and human beings . The fast response time also prevents and individual plant component trip causing a tripping chain reaction and un –necessarily shutting down the entire plant. This system provides operating personal with which the necessary tool to increase overall plant availability and efficiency . Such system have been adopted at various power station viz Dhanu TPS, Chandanpur power plant , koradi TPS etc in India.



POLLUTION CONTROL

Due to poor quality of coal , daily we are separating out about 300 MT ash from the flue gasses coming out from the boilers with the help of wonderful device known as ESP (Electro static precipitator) installed in between boiler flue gasses discharge after air preheaters and I.D fans . This ash is pulled out from the bottom of ESP hoppers with the help of vaccum and brought to ash plant. Here it is mixed up with water and disposed to waste land area known as dykes, at the right side of river sabarmati.

Diagram of a typical coal-fired thermal power station



Typical diagram of a coal-fired thermal power station:-

1. Cooling tower 10. Steam Control valve 19. Superheater

2. Cooling water pump11. High pressure steam turbine

20. Forced draught (draft) fan

3. transmission line (3-phase) 12. Deaerator 21. Reheater4. Step-up transformer (3-phase) 13. Feedwater heater 22. Combustion air intake5. Electrical generator (3-phase) 14. Coal conveyor 23. Economiser6. Low pressure steam turbine 15. Coal hopper 24. Air preheater

7. Condensate pump 16. Coal pulverizer 25. Precipitator

8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft) fan9. Intermediate pressure steam turbine

18. Bottom ash hopper 27. Flue gas stack

CYCLE

We can devide this process in various cycles as follows:-

1. AIR CYCLE : SECONDARY AIR


http://en.wikipedia.org/wiki/Flue_gas_stack

http://en.wikipedia.org/wiki/Bottom_ash

http://en.wikipedia.org/wiki/Steam_turbine


http://en.wikipedia.org/wiki/Centrifugal_fan

http://en.wikipedia.org/wiki/Steam_drum

http://en.wikipedia.org/wiki/Surface_condenser

http://en.wikipedia.org/wiki/Electrostatic_precipitator

http://en.wikipedia.org/wiki/Pulverizer

http://en.wikipedia.org/wiki/Condensate_pump

http://en.wikipedia.org/wiki/Air_preheater

http://en.wikipedia.org/wiki/Coal


http://en.wikipedia.org/wiki/Economiser

http://en.wikipedia.org/wiki/Conveyor

http://en.wikipedia.org/wiki/Coal

http://en.wikipedia.org/wiki/Three-phase

http://en.wikipedia.org/wiki/Electrical_generator

http://en.wikipedia.org/wiki/Combustion

http://en.wikipedia.org/wiki/Feedwater_heater


http://en.wikipedia.org/wiki/Transformer

http://en.wikipedia.org/wiki/Deaerator


http://en.wikipedia.org/wiki/Electrical_power_transmission

http://en.wikipedia.org/wiki/Centrifugal_fan



http://en.wikipedia.org/wiki/Cooling_tower_system

http://en.wikipedia.org/wiki/Superheater

http://en.wikipedia.org/wiki/Control_valve

http://en.wikipedia.org/wiki/Cooling_tower

http://en.wikipedia.org/wiki/File:PowerStation2.svg

http://en.wikipedia.org/wiki/File:PowerStation2.svg


For burning anything we need air . In the Boiler we need air to burn oil and coal to heat up water for forming steam to run turbine. For air we normally have two F.D fans(forced draft). These Fans are sucking air from the atmosphere . The air so sucked is passed through SCAPH (steam coil air preheater) for primary heating.Than this air is passed though air Pre heater . Here the air is heated up with the help of flue gases temp. After the air heating at preheater it comes to windbox and thereafter goes to boiler for burning the fuel.

AIR CYCLE : PRIMARY AIR

This air is also sucked from the atmosphere by primary air fans. These fans may be two in numbers or individually one for each coal mill. The air sucked by the fans goes to 2/3rd portion of air pre heaters . After the air being heated up at air pre heater comes to coal mills and from here the mixtures of coal and air goes to boiler furnance. This way the primary air has two functions .

1. Being used as carrier of coal mill upto boiler and2. After reaching to boiler furnance it takes part in combustion.

2- OIL CYCLE: L.D.O(LIGHT DIESEL OIL)

Initially the boiler furnance is lit up using L.D.O coming from Gujarat refinery by road tankers with help of pumps these tankers filled up of LDO are emptied in LDO tank .from the tank the LDO is pumped to boiler furnance at elevations AB from four corners i.e AB-1,2,3&4 . here the burns in the furnance with the help of ignitors.

OIL CYCLE: R.F.O (RESIDUAL FUEL OIL)

As the LDO is costly one so after achieving some temp. and pressure the LDO is replaced by RFO . this RFO oil is also coming from Gujarat refinery by railways . after oil reaches to tps , it is heated up with the help of steam. After the oil being heated up , the same is transferred to FRO tanks . from the tanks the oil is pumped to boiler furnance at elevation AB, CD and EF from corners 1,2,3&4 . in order to maintain the temperature of the RFO the carrier lines are supported by heat tracing lines which may be by steam or electricals heaters .

3- COAL CYCLE

In order to generate to Power to the tune of MW daily we need about Mts coal which is coming from far away coal Mines situated in M.P/Bihar/orissa etc. First the coal wagons through Railway track comes to wagon trippler. Here the wagon are emtied with the help of wagon trippler by turning it down to 180. From here the coal comes down to big hooper below 00 level. From the hooper the coal with help of conveyor belts is taken to primary crusher. Here the coal is crushed to a very small size. The Coal after Primary crusher goes to secondary crusher . Here coal is crushed to very small size of about one inch .After the secondary crusher the coal with help of conveyer belt comes to big bunker having capacity of about 500MT each. From the bunker the coal with the help of coal feeder comes to coal mills and here the coal is crushed to very fine powder to about 200 mesh size. This powder coal



with the help of primary air is taken to boiler furnace from elevation A B C D E & F and corners 1,2,3,4. and purns for heating the water in side water walls to from steam to run the turbine.

4- WATER AND STEAM CYCLE

For generating power to about 660 MW we need lot of water and the same is arranged from river sabarmati from three French well. Each well is having three pumps of 200 KW each. The water pumped , mainly devides to three parts (1) to overhead tank to meet with colony requirement. (2) for the make up of cooling water (C.W. system) and the (3) major part is stored in a big sump . At the sump some primary alum chlorine treatment is given to the water and then the water is taken to D.M water is than coming to CSTs situated very near to boiler for filling up the boiler and thereafter making up the wter losses initially the boiler drum filled up with water to its half (4) level. From boiler drum the water goes to water walls . here the water is initially heated up and the steam formed in the water wall goes to upper half of the boiler drum from upper half of the boiler drum the stem goes to superheater (14) no. from the final 14 no. superheater the steam coming out is known as superheated steam having a pressure of 155 kg/cm2 and temperature of 540 c (210 MWsize) . this steam is taken to turbine through steel pipe line to run the HP turbine . the turbine is mainly divided in three parts . the main steam roils the HP turbine and after its energy being utilised in rolling the turbine the CRH (cold reheat) steam is taken back again to reheaters in boiler turbine and from here it goes to LP turbine. Fro LP turbine the steam in condenser is collected in hot well . from hot well the water is pumped to various heaters and finally reaches to deaerator . in the dearator the dissolved air is separated out and the water collected at the bottom of the dearator comes to the suction side of feed pumps . these pumps are of very high rating to pump the water from 00 to 54 mts level .

From boiler feed pump discharge water goes to boiler drum through HP heaters and economisers . and this way the whole water and steam cycle continous.

5- T.G.CYCLE:

By generating the steam in boiler we run turbine to 3000 RPM to rotate the generator rotor .The generator rotor is charged by exciter rotor to generate flux and flux is cut in the stator windings and EMF is produced and this is called electricity .The Power produced/ generated p=√3VI cos Ө = 1.732* 15.75 KV * 9050 Amps *0.85 = 210 MW.The power generated is at the vo;tage of 17.75 KV For transmitting it to various sub-stations it is stopped upto 220 KV by generating transformer (GT). After stepping up the voltage the power comes to 220 bus bars A& B from here through 220 kv double circuit lines it is transmitted to various substation i.e Ranasan/chhatral/soja (Nardipur). At these sub-station the power is further stepped down to 132 KV and transmitted to other 132 kv S/s and from here to 66 kv S/s and then to 11 KV and then 440 volts and 230 volts for utilising the same for residential agriculture and industrial purpose.

6- C.W.CYCLE (CIRCULATING WATER/COOLING WATER):

As mentioned above after rolling turbine (LP) steam is dumped to condenser for converting in to water. The condenser is mainly devided in four part e.g. left,right,top and bottom in the



condenser there are thousands of steel tubes and gets cooled down to water.where as cold water coming from the bottom of the cooling tower duly pumped by CW pumped comes inside steel tubes of the condenser get heated up.This hot water inside the condensor tubes from bottom left and right side of the condenser come to top R and L side of the condenser and then taken to the cooling from getting cooling the hot water falls from the height of about 8 mts duly spreaded in to fine showers and gets cooled down. The cooling effect is due to very high height of the cooling tower wich creates a natural draft (air circulation) At top of the cooling tower air pressure remains low where as at bottom of the cooling tower it is (air pressure ) high. Thus air blow/flows from bottom to top side of the cooling tower and water falls from top to bottom and gets cooled down by coming in contact of air circulating. The loss in cooling water is make up by French well water mentioned initially in water /steam cycles.

7- FLUE GASES CYCLE:

As already mentioned earlier for forming steam we have to burn oil and coal in the boiler furnace with the help of Primary and secondary air. After coal burning smoke is formed. This is known as flue gases are coming out from the Boiler contains CO2 , SO2, and huge quantity of ash particles as the quality and contains about 40% ashes . As already mentioned in coal cycle daily for generating power to about 660 MW we need coal to about 8500 Mts . and as just mentioned the ash contained are about 40% we have to separate the ash of about 2600 mts from the flue gasses coming out from the boiler 1st the flue gasses are coming to economiser. Here the feed water is heated up by conduction method. Thereafter the flue are coming to air preheater A&B here the flue gasses temp is utilised for heating primary and secondary air. After this from outlet/discharge side the flue gasses enters to ESP. here the ash particles contain in the flue gasses are separate out and pure smoke with the help of ID fan is thrown to atmosphere through chimney . the ash particle separated out in ESP falls in the bottom hoppers of ESP with the help of rapping mechanism . from the hoppers the ash collected is brought to the ash plant with the help of vaccum & here in ash plant the ash is mixed with water & slurry is found . this slurry is than pumped to big dykes through pipe line . when one filled up the pipe line are shifted to other dykes . the dykes filled up earlier isleft open for some time for drying out and half feet is spreaded over the dyke and on this upper surface of the dyke plantations is done. At gandhinagar we have planted thousands of trees and the results are very good.Over and above , six to seven major cycles there are many other cycles also e.g ACW system , BCWsystem , service air , instrument air cycle , stator water system, seal oil system , 6.6 KV control room , 440 volts control room, excitation system , air washery system, switch yard , fire fighting , LDO/FO pump house, CW pump house , DM plant , coal plant HP/LP bypass , PRDS,DAS, ATRS and many others , which may need separate detailed study.

Process description

A generating station converts heat energy of coal combustion into electrical energy is know as thermal power station.



Steam is produce in the Boiler by utilizing the heat of coal, Lignite,oil or gas combustion. Steam is then expanded in the prime mover (i.e. steam turbine) and is condensed in a condenser to be fed into the boiler again. The steam turbine drives the alternator which converts mechanical energy of the turbine into electrical energy. This type of power station is suitable where coal and water available in abundance.

As per energy conversion as shown in figure a , chemical energy of fuel is converted into heat energy in the furnace and water is converted into steam in boiler. Now in steam turbine heat energy is converted into mechanical energy. Alternator coupled with steam turbine which converts mechanical energy into electrical energy.

Important Equipments in Thermal Power Station

Different Equipments are used in Thermal Power Station. Mainly they are grouped into two:-

(1) Mechanical Equipments:-

a) Boiler Furnace and Steam Drumb) Super Heater-Radiant Super Heater & Convection Super Heater.c) Economiser.d) Air Preheater.e) Pumps.f) Condensor-Jet Condenser & Surface Condenser.g) Prime Mover-Impulse Turbine & Reaction Turbine.

(2) Electrical Equipments:-

a) Alternator.b) Exciter.c) Transformer-Main Transformer ,Station Auxiliary,& Unit Auxiliary.d) Switch Gear-Circuit Breaker,Relays,Switches,& Control Devices.



5.1 Boilers



The main Parts of Boiler

Drum



Super heater Reheater Economizer Air Preheater Furnace Feed Water Heater Deaerator

Boiler is a device meant for producing steam under pressure. Steam boilers are broadly classified into fire tube and water tube types. Generally water tube boilers are used for electric power station.

If the hot combustion gases are restricted to inside the tubes and the tubes are surrounded with water the boiler is a fire tube boiler while if the arrangement is opposite, i.e. water is inside the tubes and hot gases are outside the tubes, the boiler is water type.

Fire tube boilers have low initial cost, are more compact but are more likely to explode. Further, because of water volume being more and circulation being poor they cannot meet quickly the changes in steam demand. For the same output the outer shell of fire tube boiler is much larger than that of a water tube boiler. Water tube boilers have less weight of metal for a given size and are less liable to explosion, produce higher pressure, are easily accessible and can respond quickly to changes in steam demand. Tubes and drums of water tube boilers are smaller than those of fire tube boilers, whereas the maximum working pressure in a fire tube boiler is limited to only 17 kg/cm*cm. Gauges pressures are as high as 125 kg/cm*cm. Gauges and temperatures from 315 C to 575 C are attainable with water tube boilers. Water tube boilers required lesser floor space. In the boiler heat transfer takes place through the wall of the tubes and the drum or drums are protected from direct contact with hot flue gases. The steam is super heated in a super heater before passing through the boiler to the prime mover. The flue gas is burned in the furnace of the boiler. For efficient combustion enough air has to be supplied by natural F.D. fans. Heat is produced owing to combustion of the fuel. The gases products of combustion give most of their heat to the water in the economizer tubes. The gases then pass through an air heater arrangement thus providing initial heat to the air before it is admitted to the furnace. Finally the flue gases pass out to the atmosphere through the chimney.Arrangement for feeding fuel to the boiler furnace is discussed in a subsequent section. Air is supplied through the F.D. fans below the grate. The ash pits receive the burnt fuel in the form of clicker and ash. As stated earlier the fuel gases after leaving the boiler damper flow through the economizer, air preheater, I.D. fans to thechimney.

Water tube boilers are available in a number of different designs. They may be straight or bent tubes, longitudinal or cross drum, horizontal, vertical or in inclined tube, forced or natural circulation, single or multi drum etc.

The most important consideration in the design of water tube boiler is the circulation of water within the tubes. Special designs of boilers using high steam pressures employ forced circulation while most of the conventional water tube boilers depend upon natural circulation of water through the tubes.

Steam Drum



The boiler drum contains both steam and water, the former being tapped from the top of the drum whereas highest concentration of dry steam exists a number of accessories such as water level indicators, feed water regulators, safety valves, blow down valves, soot blowers, automatic alarms, pressure gases, etc., are usually fitted on the boiler. The use of these devices assists in adequate control and operations of the boiler as also in safety against accidents.

Each unit is having separate boilers for supplying steam to steam turbine. Each boiler is of natural circulation type and capable of generating 383 tones of steam per hour at a pressure of 147 kg/cm*cm and temperature of 540 C at reheater outlet by burning pulverized coal.

The unit is of natural circulation type with complete water furnace, tangentially fired balance draught radiant reheat type, dry bottom with direct pulverized coal with bowl mill. In natural circulation boiler the water flow from down comer end from water wall to drum is established by force created by difference in specific weight of cold and hot water.The furnace is arranged for dry ash discharge and is fitted with 20 no. of coal burner with capacity to maintain MCR (Maximum Continuous Rating) of boiler which are locked at different elevation at each four corner sandwiched between coal nozzels. The unit is provided with 5 no. of coal mills, four of which are capable to take load up to MCR.Two no. of F.D. fans are provided per boiler to provide sufficient air required for proper combustion at MCR.The no. of I.D. fans is provided per boiler to maintain the furnace draught at MCR.

The mixture of steam and water goes to the boiler drum at the top where steam is seperated from water by density difference. The dry and saturated steam coming out of the drum goes to superheat. In super heater, it is superheated to 147 kg/cm*cm and temperature to 540 C. The type of super heater used is radiant superheated which uses the radiation phenomena to heat the steam. This outlet of super heater is to HP turbine. The steam from HP turbine goes too reheated where the steam is again heated up to temperature 540 C and pressure 147 kg/cm*cm. This reheat steam goes to IP turbine to L.P turbine.

Boiler Data:-

* Furnace width : 13868 mm.

* Depth : 10582 mm.

* Volume : 5140 m*m*m.

* Fuel Heat input : 529.9*1000000 Kcal/hr.

* Height : 63 m.

Design Parameters:-

* Main Steam : Steam flow at super heater outlet690 t/hr.



Steam pr. at super heater outlet 55 kg/cm*cm

Steam temp. at super heater outlet540 C.

* Reheat Steam : Reheat steam flow 594 T/hr.

Steam pr.at RH inlet 40kg/cm*cm. Steam temp. at RH inlet 339 C.

Steam Temp. at RH outlet 244 C.

Data on Mills:-

* Size & type : BCP 2360/77.*No. of mills : 6 no. /unit.*Make : m/s steam industries FRANCE.*Basic capacity of mill : 47.t/hr for 70% through 200 mesh.with grind ability.*Mill Motor : 425 kv, 6.6 kw, 1000 rpm, BHEL.*Weight of Mill : 98.6 t. ID 2360 mm.

Data on BCW System:-

BCW storage tank capacity : 20 m*m*m. BCW overhead tank capacity : 5 m*m*M. No. of BCW pump : 2. Pump capacity : 220 m*m*m/re Delivery head/suction head : 60MWC/2.5MWC. Pump size : 150 mm+125 mm. Pump make : Kirloskar Brothers. Pump stage :

two stage, horizontalcentrifugal pump having tangentialentry and exit.

Pump Motor : 65 kw, 415 v,3 phinduction motor,1480 rpm & directlycoupled with pumpthrough flexiblecoupling.

Application of Bearing Cooling Water:-

For cooling of 2 ID fan motor bearing lubrication oil. For cooling of GR fan bearing lubricating oil.



For cooling 5 no. pulverizer gear lubrication oil. For cooling boiler auxiliary.

For cooling of sample of saturated steam.

Super heaters:-

The function is to super heat the steam to the desired temperature. By removing the last traces of moistures (1 to 2%) from the saturated steam coming out of the boiler and by increasing its temperature sufficiently above saturation temperature there is an overall increase in cycle efficiency. Decides, too much condensation (exceeding 12%) in the last stages to the turbine is avoided.

Type Heating Surface

* Low type super heater 3320 m*m.* Platen super heater 545 m*m.* Final super heater 875 m*m.

Economizers:-

The economizer is a feed water heater driving heat from the flue gases discharge from the boiler. The justifiable cost for economizers depends in the total gain in efficacy. In turns, this depends on the gas temperature out of the boiler and feed water temperature to the boiler. Regenerative cycle inherently gives height of feed water temperature. Therefore the adoption of economizers must be studied very carefully.

A boiler producing between 10 to 100 tons of steam per hour operating at 30% or more loads should be evaluated for possible retrofitting with an economizer. The cost benefits depends upon the boilers size of fuel used an exhaust gas temperature. It has been estimated that about 1% of fuel cost can be saved for every 6 C rise in the temperature of the boiler feed water. Saving upto maximum 20% can be achieved by incorporating economizer where boiler operation is very efficient.

When more heat is available, that can be used in increasing the sensible heat of the feed water or pass in through an air heater, however, in most economizer, the feed water's not heated higher that to within 25 C of the temperature corresponding to the saturation temperature of steam in the boiler thus preventing steam formations in the economizer.

Reheater (Economizer):-

Type Pendant

* Heating surface 1924 sq.mt. * No. of stages one.

Air Preheater:-

The heat carried with the flue gases coming out of economizer are further utilized for preheating the air before supplying to the combustion chamber. It has been found



that an increase of 20 C in the air temperature increases the boiler efficiency by 1%.

The air heater is not only considered in terms of boiler efficiency in modern power plants, but also as a necessary equipment for supply of hot air for drying the coal in pulverized fuel system to facilitate grinding a satisfactory combustion of fuel in the furnace.

The use of Preheater is much economical when used with pulverized fuel boiler because temperature of the fuel gases out is sufficiently large and high temperature (250 to 350) is always desirable for better combustion.

Air heater are usually installed on steam generator that burn solid fuel but rarely on gas or oil fired units by contrast, economizer are specified for most boilers burning liquid or gas or coal whether or not an air heater is provided.

The principle benefits of preheating are:

(1) Improved combustion.(2) Successful use of low grade fuel (High ash content).(3) Increased thermal efficiency.(4) Saving in fuel consumption.(5) Increased generation capacity (Kg/m*mm-hr) of the boiler.

The air Preheater must provide reliabilty of operation, should occupy small space, must be reasonable in first cost and should be accessible.

The air preheater is not essential for the operation of steam generation but they are used where a study of the costs indicates that some money can be saved or efficient combustion can be obtained by their use. The decision for its adoption can be made when the financial advantages is weighted the capital and maintenance cost of the heater. The decision cannot be taken so easily as the economic advantages of hot combustion, maintenance of furnace and the saving in heat discharged to the chimney.

The different types of air heaters which are in use are discussed below:The air preheater is generally divided into two groups as recuperative and

regenerative type.The recuperative heaters continuously transfer the heat from hot gases to cold air the

regenerative heater alternately gets heated and cooled by the hot gases and cold air. Unlike the recuperative type the regenerative is discontinuous in action and operates on cycle. In rotory regenerative type the cycle action applies to the heating and cooling on an individual element of the surface but the following steam of air receives heat continuously.

Type Bare Tube

* Heating Surface 2500 sq.mt.* No. of Blocks one.

Condensers:-

Steam after expansion through the turbine goes through the condenser the use of condenser improves the efficiency of power plant by decreasing the exhaust pressure of the



steam blow atmosphere, another advantage of condenser is that countenanced steam can be recovered and this provides a source of good and pure feed water to the boiler there by reducing considerably the water softening plant capacity. Air and noncondensable gases are also removed from the steam when it passes through the condenser.

Cooling water for condensing steam in the condenser is quite large in quantity, therefore a source of water capable of supplying water throughout the year is essential. Generally water from river is taken for this purpose by means of circulating water pumps after use, the warm water is returned to the river. If a plentiful supply of water is not available water has to be cooled and used again.

In the later case water is first obtained from a tube well or some other source and stored in a tank. From the tank it is pumped into the condenser. Generally a centrifugal pump is used for this purpose. The water there absorbs the latent heat from the exhaust steam and gets warm; the warm water is passed to a spray pond or a cooling tower.

TURBINE:-

Steam Prime Mover:-

The steam turbine has several advantages over the stem engine as a prime mover. It has a higher thermodynamic efficiency since steam can be expanded to a lower final temperature that is possible in a steam engine. The basic construction of steam turbine is simple. There is no need to piston rod mechanism and slide values; no flywheel is needed. Also a steam turbine can be build involved maintenance of a steam turbine is comparatively much simple. Problem of vibration is also much less high operating speed result in a lower weight of rotating parts for the same power.

Each turbine is of the horizontal close coupled,tandem compounded,reheat & impulse type designed for stop value steam conditions of 147 kg/cm*cm & 540 C steam exhausting from the high pressure cylinder.

The turbine has a continuous maximum economical rating of 210 MW of unit no.3 at the generator terminals at 300 rpm steam is extracted from suitable stages of the expansion to provide for 6 stages regenerative feed heating,with a final feed water temp. of 230 C.

The turbine is a single axis machine,suitably compounded so that the expansion of the steam takes place in three cylinders one high pr.,one intermediated pr. & one low pr.cylinder.


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The rotating element of the turbine consist of the high pr.rotor,the intermediate pr.rotor & the low pr.rotor,solidly coupled together to form a single shaft,supported,in five journal bearing and located axially in the turbine casing & housed in the center pedestal. The direction of rotation of the rotor is clockwise when the machine is viewed from the front pedestal.

An oil system provides low pressure oil for bearing lubrication and high pr.oil for the turbine control gearing & generator shaft sealing system. A high pr.jacking oil system is incorporated in the lubrication system to enable the completer rotor assembly to be floated in the bearing during staring and shutdown when the turning gear is in operation.

Turning gear is mounted on the rear end pedestal between the turbine and generator to provide a slow,high torque drive,sufficient to start the rotor assembly to be floated in the bearing during staring and shutdown when the turning gear is in operation.

The steam turbine is generally of two types: Impulse and Reaction.

In an impulse turbine the steam expands in the stationary nozzles and attains a higher velocity, potential energy in steam due to pressure and internal energy is converted to kinetic energy when passing through the nozzle. The type of turbine also has fixed and moving blades.

Commercial turbines use series combination of impulse and reaction types is because steam can be used more efficiently by using impulse and reaction blade on the same shaft. The


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steam expanded through the turbine from a high pressure at the throttle valve to back pressure corresponding to a vaccum of 71 to 73.5 cm Hg or an absolute pressure of 5 to 2.5 cm Hg.

In Power Plant three stages of Turbine are used for efficient usage of steam.

(1). High Pressure Turbine.(2). Intermediate Pressure Turbine.(3). Low Pressure Turbine.

The main steam rolls the HP turbine and after its energy being utilized in rolling the turbine, the cold steam is taken back to reheater in boiler for reheating. The steam so heated in reheater is known as hrh(hot reheat), it comes to the IP turbine and from here it goes to the LP turbine. From the LP turbine the steam is dumped to condenser to convert it into water. Water so converted from steam in condenser is collected in hot well. From the hot well the water is pumped to various heaters and finally reaches to deaerators. In the deaerators the dissolved air is seperated out and the water collected at the bottom of deaerator comes to the suction side of feed pumps. This pump is of very high rating to pump the water from 00 to 54 m level. From boiler feed pump discharge water goes to boiler drum through HP heaters and economizers. Thus the whole water and steam cycle is performed.

Alternators:-

Most of turbo alternators in centre power stations are 2-pole, corresponding to speed of 3,000 rpm for 50 Hz operational and 36,000 rpm for 60 Hz operation. Largest available size of turbo alternators have cylindrical rotors and therefore avoid critical speed. The rotor and stator of a turbo-alternator may be air-cooled in size upto 40 MW. Above this rating it is usually more economical to cool the rotor and stator by hydrogen. Besides, hydrogen cooling offers a number of other advantages. For turbo-alternators having rating above 150 MW hollow stator conductors may be employed, cooling of such conductors depending upon the size of the machine. Turbo alternators are usually rated at 11 KV, 3-phase star connection of stator windings being universal. Standard frequency of generation is 50 Hz. For large power systems higher voltages are employed since with higher voltage rating there is more expenditure and insulation becomes a more serious problem. Moreover in any case step up power transformer is to be used for stepping up the generation voltages for transmission.

Generally turbo-alternators are rated at 0.8 power factors lagging. Main exciters are compound d.c. generators of 115 V to 230 rating capable of supplying required excitation for main generator on full load and with an over load of about 20% at rated power factor. Minimum of 10% overload capacity under normal operating conditions is provided in case of generators. Static exciters are also now in much use.

Coal Handling Plant



In any Thermal Power plant, electrical power is generated by rotating a rotor of a generator with help of steam turbine. For, this steam is produced by heating water. Water can be heated by burning coal, diesel ,oil, or natural gas. Heat can also be obtained by fusion as nuclear energy. In Gujarat Electricity Board's Gandhinagar Thermal Power Plant Station coal is used for heating water for getting steam.

For generating one Mega Watt Power, normally 15.556 mt. coal is required, one train approximately bring about 1080 kilo. mt. to the plant..Quantity of coal required depends upon quality or grade of coal. Certain specifications of coal are as under:

GRADE Lower Limit of Calories Values in kilocalories/kg.

A 7200B 5600C 4900D 4200E 3300F 2400

Relevant Data of Coal:-

1. Total Moisture 7%2. Total Moisture in Monsoon 17%3. Volatiles 23%4. Fixed Carbon 43%5. Ash 27%6. G. H. No. 557. Density 800 kg/m

In India Coal India Limited and its subsidiary Western Coal Fields organize mining of coal and selling through their regional offices.

Coal is brought from coal mines situated in various states are Madhya Pradesh, Bihar, Orissa, Chhatisgarh, etc. The coal supplying countries are Australia, Bangladesh, etc.

Wagon Trippler:

The coal is brought through trains. The train is kept in yard. Each wagon is emptied with the help of wagon trippler.



Features of Wagon Tripplers are as under:Two types of Wagon Tripplers are deployed in GEB's TPS.

Main details are as under:

Features

Unit 1 & 2 Unit 3, 4 & 5

Make Elecon Engg. Co. Elecon Engg. Co.Type Side discharge RotaryAngle of tilting 150 170Weight bridge 100 mt. 280 mt.Capacity 12 boxes/hr 20 boxes/hrMotor 80 hp-900 rpm 60 hpCommon Hopper Capacity 210 mt. 300 mt.

Method:

Coal from Wagon Trippler is collected in big hoppers, which are situated below ground level. From hopper coal is taken to primary crusher through apron feeder. Apron feeder is big steel chain, which is capable of sustaining weight of lumps of coal boulders falling from wagon trippler.

Big lumps of coal are crushed to a small size about 200 cm*cm*cm, this coal is taken to crusher house with help of conveyor belt and it goes to crusher house.

Hopper is situated on ground. The apron feeder, crusher, conveyor belt, etc., are located underground. The depth of plant is about 22 m below ground.

The crusher house is about 20 m above the ground. Prior to feeding the coal from conveyor belt into crusher house, any metal pieces present in coal are separated out. For this metal deflectors are placed near conveyor belt in transform tower.

If the metal particles are not separated from coal, then metal particles may damage the crusher jaws, stones, etc., present in coal, are separated manually.

In the crusher house the coal brought by conveyor belt is sent to roller screens(RS). Here the small size coal particles are separated and big lumps are transmitted to ring grinder(RG). Here the coal is grinded and brought to size of about 1 cubic inch.

The coal from RS & RG that falls on conveyor belt is taken to bunker. The trolley is used to drop the coal in different bunkers. Bunker is a big hopper, like container having capacity of 500 mt. each.

Features of Coal Crusher are as:



Total No. : 2 no.Capacity : 250 tones/hr.

Electrostatic Precipitator

ESP is an important device in operation of power plant. ESP is used to seperate out ash content from the flue gases so as to reduce air pollution and increases efficiency of chimney. ESP, as an assembly consists of Electronic Controller, Transformer Rectifier set and ESP itself.

ESP utilizes electrostatic forces to seperate dust particles from the gas to be cleaned. The flue gases are passed through the chamber containing vertical steel plants. These plates divide the chamber into number of parallel paths for passage of gas. A frame with electrode is located within each passage. High voltage negative DC supply is applied between electrode and found, which creates a strong electrical field between electrodes and steel plates. The electric field becomes strongest near the surface of wires, so strong that an electrical discharge i.e. the corona discharge develops along the wires. The fuel gas is ionized due to corona discharge and large quantities of positive and negative ions are forced. The positively charged ions are immediately attracted towards the negative wires by the strenght of electrical field. The ions collide with ash particles and in turn ash particles are also charged and deposited on the ash plates. Using rappers the ash is collected into hoppers while flue gases are drained out by induced draft fan through chimney.

Electrostatic Precipitator

Deaerator



Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal water storage section

A steam generating boiler requires that the boiler feed water should be devoid of air and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal.

Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.

There are many different designs for a deaerator and the designs will vary from one manufacturer to another. The adjacent diagram depicts a typical conventional trayed deaerator.If operated properly, most deaerator manufacturers will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm³/L)

Switch yard

The components are listed as follows. In order of arrangement from, power line to utility.


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Equipments:-

(1). Lightning Arrestor.(2). Relays.(3). Circuit Breakers.(4). Isolator.

(5). Insulator (6). Earthing Switch.(7). Transformers.

Lightning Arrestor:-

Light is one of the most serious cause of over voltage. If the power equipment especially at door Sub Station is not protected the over voltage causes burning of insulation. Lightning is a huge spark causes by electric discharge taking place between clouds, within the clouds and earth.

Various types of lightening arresters in use today are listed below:

(1) Rod gap type(2) Horn gap type(3) Multi gap type(4) Expulsion type (5) Valve type or Thyrite type(6) Metal oxide gapless type

The lightening arresters used in the plant are thyrite type lightening arresters & Zns(a metal oxide) gapless type arresters. A material used in lightening arrester should have the characteristic of resistance decreasing with the voltage across it increased. Thyrite is one such compound of ceramic nature. Across this if voltage is doubled, current increases 12.6 times. The series gap provided to prevent current from flowing at the normal voltage. At IFFCO Kandla plant, in switchyard horn gap type lightening arrester are used.

Relays:-



An electrical device to initiate a part of an electrical installation or to operate an alarm signal in the event abnormal condition or a fault.

A. Secondary indirect acting Relays:

This group of relays includes practically all kinds of relays for e.g. current, voltage, power impedance reactance frequency whether minimum or maximum.

B. Secondary direct acting Relays:

A group of over current and under voltage designed to operate instantaneously or with time lag these are primarily relays of electromagnet type, which are built into C.B. operating mechanisms.

Function of Protective Devices:

1. To sound an alarm so that the operator makes some corrective action.

2. To close the trip circuit of circuit breaker so as to disconnect a component during an abnormal fault condition such as overloads, under voltage temperature rise etc...

3. To disconnect the faulty parts as quickly as possible to minimize the damage to the fault part.

4. To localize the effect of fault by disconnecting the faulty part from healthy part causing least disturbance to the healthy system.

5. To disconnect the faulty part as quickly as possible to improve the system stability and service continuity.

Classification of Relays:-

Depending upon there principle of operation they are classified as under:

(1). Electromagnetic Attraction Type:-

This relay is operated by virtue of plunger of being drawn into a solenoid or an armature being attracted towards the soles of an electromagnet respectively.

(2). Induction Type Relays:-

In this type of relay a metal is allowed to relate between two electromagnets. The fields produced by the two magnets are displaced in magnitude and phase. The torque is developed by interaction on the flux of one of the magnets and the eddy current induced with disc by the other.

(3). Thermal Relays:-



They operate due to action of heat generated by the passage of current through the relay element. The strip consist of two metals having different coefficient of expansions and firmly fixed together the length so that different rates of thermal expansions of two layers of metal cause to the stroke to bend when current is passed through it this principle is used in this relay.

(4). Static Relays:-

Static relays contains electronic circuitry, which may include the transistors, ICs, diodes and other electronic components. There is a comparator circuit in the relay, which compares two or more currents or voltage and gives an output, which is applied to either a slave relay or thyristor circuit. The slave relay is an electromagnetic relay, which finally close the contact. A static relay containing a slave relay is semi-static relay. A relay using a thyristor circuit is a wholly static relay. Static relay possess the advantages of having low burden on the C.T. & P.T. fast operation.

(5). Microprocessor based Protective Relays:-

Microprocessor based Protective relay is the latest development in this area. With the development in VLSI technology, sophisticated and fast microprocessor is coming up. Their application to the problem of protecting relaying schemes is of current interest to power engineers. The inherent advantages of microprocessor based relays with or a very limited range of application, are attractive flexibility due to their programmable approach.

(6). Moving Coil Relays:-

In this relays a coil is free to rotate with magnetic field of a permanent magnet. The actuating current flows through the coil. The torque is produced by the interaction between the field of permanent magnet and field coil.

(7). Distance Relays:-

This type of relay operates when the ratio of the voltage and current change beyond a specified limit.

(8). Differential Relays:-

Operation takes place due to difference of Electrical quantities.

Relays can be classified also depending upon their applications also:

(1). Over voltage, over current and over power relays in which operations takes place when the voltage, current or power rises above a specified value.

(2). Under voltage, under current and under power relays in which operations takes place when the current frequency or power fall below a specific value.

(3). Direction or reverse current relays are the relays in which operations occurs when the direction of applied current changes.

Relays can be classified according to their operation:



(1). Definite - time over current relays:

A definite time over relay operates after a predetermined time when the current exceed its pick-up value. The operating time is constant irrespective of the magnitude of the current above the pick-up value.

(2). Instantaneous over current relays:

An instantaneous relay operates in definite time when the current exceeds its pick-up value. The operating time is constant irrespective magnitude of current. There is no intentional time relay.

(3). Inverse time over current relays:

An inverse time over current relay operates when the current exceeds its pick-up value. The operating time depends on the magnitude of the operating current. The operating time decreases as the current increases.

Data required for Relay Setting:-

(1). A single line diagram of the system, which should give the ratings and impedance of rotating parts, transformer, feeders etc.

(2). Maximum and minimum values of short circuit currents at all the relay points.

Circuit Breakers:-

Both the lines A&B are independently capable to take up complete load of plant. Still under normal working condition both the lines shall be energized to share load among them. In case of one of the lines fails, it is possible to interconnected two 66KV side by closing circuit breaker. In case of the failure of the transformer or any of control gears fails, it possible to supply complete load from the other transformer by closing 3.3KV bus tie switch gear. It is an automatic switch of high capacity. It can make or break the normal as well as abnormal condition.

The most general way of classification of circuit breaker is on the basis of medium use for arc extinction.



(1)Air break circuit breaker(2) Air blast circuit breaker(3)Vacuum circuit breaker(4) Oil circuit breaker(5) Sf6 (sulphur hexa fluoride) circuit breaker

It is an automatic switch of high capacity. It can make or break the normal as well as abnormal condition. Air break circuit breaker, Air blast circuit breaker, Oil circuit breaker& Sf6 circuit breaker are the types of circuit breaker, vacuum circuit breakers are used in MASS.There are three types of C.B. as explained below:

(1). SF-6 Circuit Breakers:Sulphur hexafluoride is an inert, heavy gas having good dielectric and have

extinguishing properties. The dielectric strength is increased with pressure and is more than various manufactures for rated major types have developed that of dielectric oil at a pressure of 3 Kg/cm*cm.

Several Types of SF-6 C.B. are as follows:

(1). Single Pressure Type.

(2). Doule Pressure Type.At ginger switch yard in 220 KV single types C.B. are used.Specification & Rating of SF-6 C.B.:For 220 KV, Make H.B.B.

* Rated Voltage : 245.* Trip coil voltage and close coil voltage : 220 V DC.* Rated frequency : 50 Hz.* Impulse Voltage : 1.2/50 Hz 1050 KV.* Normal Current : 2500 Amp.* Gas weight : 21 Kg.* Breaking Current : SF-6.

* Weight : 6 Kg/cm*cm (at 200 C). * Symmetric : 40 KA. * Asymmetrical : 48 KA. * Mass : 3900Kg. * Short current time : 40 KA/3 sec.

Merits of SF-6 C.B.:



* The breaker is silent and does not make sound like A, B, C, D, during operation.

* Excellent insulation is extinguishing physical and chemical properties of SF-6 gas are greatest advantage of SF-6 C.B.

* Ample overload margin for the same size of conductors.

* The same gas is circulated in the circuit hence requirement of SF-6 is small in the long run.

* No over voltage problem.

Demerits:

* Sealing problem arises.

* Imperfect joints lead to leakage of gas.

* In flux of moisture in the gas system is very dangerous to SF-6 gas C.B.

* The single pressure SF-6 is generally slower than A, B, C, D.

Vaccum Circuit Breaker:

VCB incorporates a specially designed and completely vaccum interrupter to perform its basic function of opening and closing when called up to do so, both under normal operation condition and under fault conditions as short circuit..When two currents carrying contacts are separated in a vacucm module, and arc in drawn between them. An intensely hot spot is created at the instant of contacts separation from which metal vapour shoot off, constituting plasma. The amount of vapour in the plasma is proportional to the rate of vapour emission from the electrode, hence to arc current. With alternating current arc, the current decreases during a portion of wave, and tends to zero.

There by the vapour emission tends to zero, the remaining metal vapour condenses and the dielectric strength builds up rapidly, and restriking of arc is prevented. This principle is used in vacuum circuit breaker. The vacuum circuit breaker comprises of one or more sealed vacuum interrupter units per pole. The moving contact in the interrupter is connected to insulating operation mechanism. The contact travel is of the order of a few millimeters only. The movement of the contacts within the sealed interrupter unit is permitted by metal bellows.

In VCB type VK upto 2000 A ratings, the vaccum interrupters also provide adequate inter phase to earth segregation. The barrier is mounted on the rear side of VCB mechanism cabinet.

A spring operating mechanism mounted inside a sheet steel cabinet is used to provide the energy required for the operations.

Working of Operation Mechansim:



Charging Operation:

Initially the VCB is opened and closing spring is discharged. Charging of closing spring is done either manually or electrically through a motor. The charged/discharged inductor shows the status of closing spring.

There are two types:

(1). Manually Charging.(2). Motor Charging.

Closing Operation:

When the springs are fully charged, the linkages attain certain positions, now VCB is Ready for closing operation.

Manually closing.Electric closing.

Opening operation.

When the VCB is closed the linkages attain certain position and breaker is ready for opening. There are two types as follows:Manually opening.Electric opening.

The VCB is provided with a facility of auto re-closing. This feature is achieved since it is possible to share the closing springs as soon as they get discharged, during closing operation. The mechanism is thus kept ready to re-close the VCB as soon as it is opened.

Interlocks:

Interlocking mechanism provided by VCB and cubicle ensures safeoperations, protection to personal and the correct sequence of operations.

Air Blast Circuit Breakers:



At Gandhinagar in 220 KV switch yard A, B, C, D, type C.B. are as under:

Specifications and Rating of A,B,C,D.

* Rated Voltages : 245 KV.

* Frequency : 50 Hz

* Normal Current : 2000 Amp.

* Breaking Current : 31.4 KV.

* Asymmetrical : 35.4 KV.

* Mass : 1630 Kg.

* Short time Current : 55 KA.

* Time coil Voltages : 220 V DC.

* Impulse Volatges :1.2/50 Y.5 1050 KV peak.

* Operating Pressure : 27 to 31 Kg/cm*cm.

Air blast C.B. is used today from the 11 to 1100 KV for various applications.

They offers several advantages such as faster operations, suitability for repeated operations, auto re-closer, unit type multi-break construction, simple assembly, modest maintenance etc., a compressor plant is necessary to maintain high air pressure in the air receiver. A,B,C,D are especially suitable for railway and air furnaces where the breaker operates repeatedly.

Construction of an Air Blast C.B.:

In air blast C.B. high pressure air is forced on the arcs through a nozzle at the instants of constant separation. The ionized medium between the constant is blown by the blast air. After the air extinction, the chambers are filled with high pressure air.

* Reliable operation due to external source of extinguishing energy.* Air can be used at high pressure.* Clean, non-inflammable.* Freely available everywhere.* High speed of operations.* Clean service no need of maintenance.

Isolators:



Isolators are disconnection switches. Which operates under no load condition. Isolators are designed to open and close under no load condition. Isolators do not have rated making current or breaking current capacity.

To prevent Mal-operation, the isolator is provided with inter-locking.

Inter locking between three poles for simultaneous operation. Inter locking with the C.B.

Types of Isolators:

* Vertical break type.

* Horizontal break type.

* Center break.

* Double break.

* Vertical Pantograph type.

(1) Double Break Isolator:

An isolator is a disconnecting or isolating switch, operates under NO LOAD condition only. They are to be used in connection with circuit breaker. The main function of isolator is to isolate the equipment or the part of the system as and when desired for maintenance or other purpose. There are types of isolator:

(1) Single break isolator(SBI)This type of isolator disconnects the circuit and it is open on one side of contact.

(2) Double break isolator (DBI)This type of isolator disconnects the circuit and it is open on both sides of contact.

In switch yard DBI are used.

INSULATOR



Insulators are used as a link between line conductor and line supports cross arms. Insulator prevent the leakage current from the line conductors to the earth througharms.

From O.H. transmission lines following four types of insulators are used.(1) Pin type insulator.(2) Suspension type insulator.(3) Strain type insulator.(4) Shackle type insulator.

Suspension & strain types insulators are used in the project and as explained below.

Suspension Type:

In pin type for very higher voltage (more then 66kv ) becomes complicated,bulky and costly . In case damage whole pin insulator is required to be replaced and service is disturbed.For higher voltage it is more suitable economical, and convenient to use suspension insulators. They are designed for normal 11kv working voltage.Hance as the line voltage increases 11kv, 22k, 66kv and so on, numbers of insulators are joined in series to from a string of insulator. It is nowa practice to use suspension type insulator.In the string of insulator, if one of the insulators is damaged, that particular unit is required to replaced by new one.Suspension type insulators are also called disc type insulators and also as a tension insulators are mainly of two types.

Ball and socket type or cemented type.Tongue and clevis type.

Strain Type

When the over head line teminates i.e. there is dead end of the line, or there is sharp turns of the line or a corner, much more tension is observed in the line. In order to withstand the tension on the line strain insulator can be used . The disc of strain insulator are kept in the vertical plane. For heavy strain, strain insulator string is used or some times to or more strings are connected in parallel to handle more strain.

Earthing Switch:-Earthing switch is connected between the line conductor and the earth.Normally it is one when the line is disconnected. The earthing switch is closed so as to discharge the voltage trapped on the line and is disconnected.Normally the earthing switch is mounted on the frame of isolator.Sequence of operations while opening/closing a circuit.While opening.........* Open circuit breaker.* Open isolator.* Close earthing switch.

Transformers:-



Two types of Transformers are used in Switch Yard:

* Current Transformer.

* Potential Transformer.

(1). Current Transformer:

The function of C.T. is to transform the high current in an electrical power system to lower value, which are convenient for the operation of associated instrument of protective device. It also serves simultaneously to isolate these measuring instrument of protective device from the high voltage power circuit. Current transformer is used to step down the current for metering and protective relaying purpose. The primary winding of the C.T. is connected in series with the circuit whose current is to be sensed, and across the secondary of CT the operating coil of the CT or the meter terminals are connected. CT used for metering will not have taps, as a fix primary secondary current relationship is always required. When full load current is flowing in the primary, the secondary current is usually 5 A rated. While CT used for protection have taps so that secondary current can be a varying function of primary current.

Measuring C.T.:

Measuring C.T. is intended to supply the indicating instrument, in degrading meters and similar apparatus. It has to be accurate in specified working and integrating meters.

Protective C.T.:

Protective C.T. is intended to supply current to the protective device. It is also general to have such accuracy class at normal current but on the contrary degree or accuracy on current in fault condition such as over current etc.

Construction:



The C.T. has two windings-one is primary and second is secondary winding. The primary conductor have high voltage with respect to earth. Hence it is insulated by means of an insulator column filled with dielectric oil. The normal rated secondary current is 5 Amp. Sometimes the voltage of 5 Amperes or 1 Ampere is also taken as secondary current. Some details are shown below:Specification of C.T. for 220 KV type:

* Make : W.S. insulator of India Ltd.* B.I.L. : 46080 (rhs)/1050 (peak).* Frequency : 50 Hz.* S.T.current : 40 KA.

Polarity making:

Each CT should be tested to verify that polarities making on the primary and secondary winding are correct.

CT ratio check:

Using primary injection set carries out this check. The test set compresses of a portable injection transformer arranged to operate from the local main LT (low tension) supply and having several low voltage heavy current winding. The injection transformer is usually of about 10KVA rating with a typical ratio 250/10+10+10 Volts. This permits current up to 250 A.

Potential Transformer:

It steps down the voltage of high voltage system making suitable for the relay operation and to measures high voltage. To measure high voltage, voltmeter is connected on secondary side of potential transformer i.e. on low voltage side and calibrated for high voltage measurement, as reduced voltage is proportional to high voltage. It isolates electrically proactive relay and measuring circuit from the main HV circuit.

Power Transformer:


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It is static device which transform electric energy from one circuit to other circuit without changing its frequency. It works on the Faraday’s low of electromagnetic induction. It is an electric circuit which linked by a common magnetic circuit. When the output voltage of the transformer is higher then its input voltage it is called step up transformer or in either case it is called step down transformer. Its basic construction requires no moving parts so there is no friction or winding losses typical transformer at full load lie between 96%.

Fittings & accessories of transformer:

1) Primary winding2) Secondary winding3) Oil4) Oil conservator5) Temperature recorder6) Oil cock7) Tap changer8) Radiating tube 9) Bushing10) Breather11) Buccholz relay12) Explosion went

There are four transformer installed in our 66KV switchyard. Three transformers are of 5 MVA rating & one is of 10 MVA.

Tap Changer:

Transformers are necessary for stepping down AC voltage level for long distribution and utilization system with high efficiency. Distribution voltage can be automatically regulated by means of OLTC (On Load Tap Changer).

OLTC are fitted with the transformer 4 wire 3 phase AC distribution system is obtained from the star connected secondary side of substation transformer. Utilization transformer are necessary with power utilization devices for obtaining require voltage, for on line regulation of supply voltage for controlling power input to load to match with the load.

Auxiliary systems



Fly ash collection

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan. The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent transport by trucks or railroad cars.

Bottom ash collection and disposal

At the bottom of the furnace, there is a hopper for collection of bottom ash. This hopper is always filled with water to quench the ash and clinkers falling down from the furnace. Some arrangement is included to crush the clinkers and for conveying the crushed clinkers and bottom ash to a storage site.

Boiler make-up water treatment plant and storage

Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blowdown and leakages have to be made up to maintain a desired water level in the boiler steam drum. For this, continuous make-up water is added to the boiler water system. Impurities in the raw water input to the plant generally consist of calcium and magnesium salts which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts have to be removed from the water, and that is done by a water demineralising treatment plant (DM). A DM plant generally consists of cation, anion, and mixed bed exchangers. Any ions in the final water from this process consist essentially of hydrogen ions and hydroxide ions, which recombine to form pure water. Very pure DM water becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up. The storage tank for DM water is made from materials not affected by corrosive water, such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air. DM water make-up is generally added at the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets deaerated, with the dissolved gases being removed by an air ejector attached to the condenser.

Oil system

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic oil system required for steam turbine's main inlet steam


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stop valve, the governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes over the functions of the auxiliary system.

Generator heat dissipation

The electricity generator requires cooling to dissipate the heat that it generates. While small units may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. This system requires special handling during start-up, with air in the chamber first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air.

The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV and water is conductive, an insulating barrier such as Teflon is used to interconnect the water line and the generator high voltage windings. Demineralized water of low conductivity is used.

Generator high voltage system

The generator voltage ranges from 11 kV in smaller units to 22 kV in larger units. The generator high voltage leads are normally large aluminum channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum bus ducts and are supported on suitable insulators. The generator high voltage channels are connected to step-up transformers for connecting to a high voltage electrical substation (of the order of 110 kV or 220 kV) for further transmission by the local power grid.

The necessary protection and metering devices are included for the high voltage leads. Thus, the steam turbine generator and the transformer form one unit. In smaller units, generating at 11 kV, a breaker is provided to connect it to a common 11 kV bus system.

The crushed coal is conveyed from the storage pile to silos or hoppers at the boilers by another belt Other systems


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Monitoring and alarm system

Most of the power plant operational controls are automatic. However, at times, manual intervention may be required. Thus, the plant is provided with monitors and alarm systems that alert the plant operators when certain operating parameters are seriously deviating from their normal range.

Battery supplied emergency lighting and communication

A central battery system consisting of lead acid cell units is provided to supply emergency electric power, when needed, to essential items such as the power plant's control systems, communication systems, turbine lube oil pumps, and emergency lighting. This is essential for a safe, damage-free shutdown of the units in an emergency situation.

Transport of coal fuel to site and to storage

Main article: Fossil fuel power plant

Most thermal stations use coal as the main fuel. Raw coal is transported from coal mines to a power station site by trucks, barges, bulk cargo ships or railway cars. Generally, when shipped by railways, the coal cars are sent as a full train of cars. The coal received at site may be of different sizes. The railway cars are unloaded at site by rotary dumpers or side tilt dumpers to tip over onto conveyor belts below. The coal is generally conveyed to crushers which crush the coal to about ¾ inch (6 mm) size. The crushed coal is then sent by belt conveyors to a storage pile. Normally, the crushed coal is compacted by bulldozers, as compacting of highly volatile coal avoids spontaneous ignition.conveyor system.

Advantages and Disadvantages of Thermal Power PlantAdvantages:-* The fuel i.e. coal is used which is quite cheap.* Less initial cost as compared to other generating stations.* It can be installed at any place irrespective of the existence of coal.* The coal can be transported to the site of the plant by rail or road.* It requires less space as compared to the Hydro electric power station.* The cost of generation is lesser than that of the diesel power station.

Disadvantages:-

* It pollutes the atmosphere due to the production of large amount of smoke and fumes.* The Efficiency of coal plant is overall low(approximately 30%).* It is costlier in running cost as compared to the Hydro electric plant


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CONTROL SYSTEM

AUTO CONTROL SYSTEM

Auto control system performs the following functions;

1) Generator voltage control.2) Undelayed limiting control for the output current of the Thyristor set.3) Limiting control for the under exited range.4) Delayed limiting control function over excited range.5) Automatic field separation during shutdown of generator.6) Delayed limiting control for the stator over current.7) v/Hz limiter to prevent over fluxing of the limit transformer and of generator.

Auto control system performs the following components:

1) Actual voltage feedback signal forming unit.2) Reactive/ Active current detection unit.3) Li miters.4) Voltage regulator unit.5) Universal amplifier.

6) Gate control.

Set Generator terminal voltage feedback is taken from generator PT. Output of PT (11GV) given to actual voltage feedback sign forming unit, which produce DC signal (-8V) proportional to generator voltage.

Output of the reactive/active detection unit, which is proportional reactive current, added vectorically to actual voltage signal to compensate for reactive drip of unit transformer/when generator is connected to the net through unit transformer.

The rectified, filtered compound voltage given as an actual value to voltage regulator is compared to actual value, reference value and limiters output. Its output (10V) is directly depends on the:

1. Differences between actual value and reference value.2. Setting of its proportional and integral feature.

Limiters intervene.

Output of AVR is given to the gate control circuit, which produces firing pulses displaced by 60, this firing pulse is given to the gate control circuit of Thyristor Bridge, Firing angle, which devices conduction period of Thyristor depends on the firing pulse. Thus according to input signature to gate control circuit, Thyristor bridge output varies and control the excitation.

MANUAL CONTROL SYSTEM



In case when any part of auto control system fails, to continue the operation, manual channel is provided. Manual channel is provided. Manual channel consists of following units:

1. Universal Amplifier2. Reference Value Generator3. Current Regulator4. Gate Control Set For Manual System

The Thyristor set input AC current which is proportional to main exciter current i.e. output DC current of Thyristor set, in sensed by using CT’s having buren resistors is AC voltage developed across the resistor is given to universal amplifier. Where it is rectifier and filtered. Output of universal amplifier is used as an actual value to current regulator; the reference value (10V) is derived from highly reliable and stabiliezed power supply by higher and lower commands. This voltage signal (10V) given as a reference value to current regulator. Current regulator compares actual values with set point and its output directly depends on

1. Difference between set point and actual value. 2. Setting of its proportional integral factors.3. Limitations of generator voltage given to current regulator.

This output of current regulator after being six firing pulse displaced by 60”. ‘1 his firing pulse given to the gate circuit of Thyristor Bridge and it controls the firing angle of Thyristor Bridge output current to set point value.

LIMITATION OF THE MANUAL CHANNEL

1. It does not ensure synchronism during transient condition.2. it controls the excitation irrespective of generator terminal voltage within

limitations given to the excitation current regulator.3. It also does not ensure safe operation of machine near operating limits.

Because of the above limitations manual channel is used only in emergencies.

MAIN FEATURES CONTROL FUNCTIONS

Voltage regulator with adjustable FID controller (AUTOMATIC MODE) Field current regulator with adjustable PI controller (MANUAL MODE) Reactive power influence (droop or compensation) Under excitation and over excitation limiters. Automatic follow-up between Automatic<->Manual as well as Channel 1<->

Channel 2. Superimposed controller for machine or T-line power factor or MVA-r

MONITORING AND PROTECTION FUNCTION

Over current, inverse time and instantaneous loss o excitation. Over fluxing protection (V/Hz relay) Converter temperature Thyristor conduction monitoring Supply voltage monitoring

BATTERY CHARGER

D.C. SUPPLY



D.C. supply is heart of the power station. Battery and battery chargers should be kept in service continuously to ensure reliable supply. The failure in D.C. supply cannot be tolerated. Battery should be always in charger condition and ready to take load in case of A.C. power supply failure. On resuming A.C. supply the battery is recharged by putting charger on boost. After charging of battery cells again charger should be put on float charging to supply station demand and keeping battery in float charging condition.

D.C. supply is used to run the D.C. motors as D.C. seat & D.C. flushing motors and D.C. emergency lighting in case of total power supply failure. Also D.C. supply is used for various control circuit such as 22KV 6.6 KV and 415 volt breakers closing, tripping and indication, Relay control circuits, MFF circuits, MARP circuits and annunciations circuits. DC system can be divided mainly into three parts.

A. STATION BATTERY:

Two battery sets are installing having 110 cells in each set two supply 220 DC two battery sets are installed having 25 cells in each set two supply 50 DC which is for boiler control desk annunciation.

B. BATTERY CHARGER FOR 220 VOLT DC SYSTEM:

The general purpose of this battery charger unit is two DC power to power station in conjunction with 110 lead acid sells to ensure an interrupter supply irrespective of AC mains supply AC input 415 volt 3- phase supply to given two battery charger from 415 volt emergency MCC.

Float charger is capable fro floating 110 lead acids sells from 1085 volt per cells 2.65 volts/cell at a maximum charging current of 80 amp. During the normal time battery is floated by means float charger, which also supplies the constant load. In case of emergency the constant load is being taken care of the battery which is connected to the bus by means of switch SW-10.

When the mains resume there is a need for the battery to be recharged since the same would have discharged during emergency. For this purpose the float/boost change over switch is kept in the boost position. During the boost charging the load is taken care of by the float rectifier in the unlikely event mains failure during boost charging, the float/boost change over switch SW-10 must be put position.

During change over of the switch from the boost to float position the continuity of supply is maintain through the silicon diode MP-3 the output supply of DC bus is kept appreciable constant.

IN BRIEF BATTERY CHARGER

Purpose of battery in power station:



1. To run D.C. emergency flushing oil pump and seal oil pump of turbine generator set in case of total supply failure of the station.

2. For D.C. emergency lighting of the station in case of total power supply failure.

3. For trip free operation of circuit breaker and reliable protection and controls in emergency. For safety of the station, it is important to maintain the batter vigilantly, for emergency services.

Points for the battery charger to be observed:

1. Check the indication for the following are ok: a. A.C. three phase main supplies input to charger.b. A.C. three phase control supply.c. D.C. output.

2. Check that the charger D.C. output voltage and current are normal.3. The charge/discharge meter indicates whether the battery to getting

charged or discharged. See that the meter indicated the charging condition of the battery.

4. See that no alarm is persisting. No abnormal indication to appearing.5. See that the battery charger is clean.

BIBLIOGRAPHY

Sr. No. Name of the book Author

1. Switchgear and protection R.P.Ajwaliya

2. Electrical Power System J.B.Gupta

3. Electrical machine B.L.Theraja

4. Power System V.K.Mehta


Gujarat State Electricity Corporation Limited

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Transcript of Gujarat State Electricity Corporation Limited