ACKNOWLEDGEMENT

ACKNOWLEDGEMENT

For an Engineer it is very important to have proper matching between theoretical knowledge gained from the books and the practical knowledge. Although an Engineer can only be successful through sheer hard work. But the contribution of his teachers and all those who have been helpful cannot be overlooked.

Through this acknowledgement I would like to grab the opportunity to thank all those who have helped me right from the start of my training upto its end.

I would also like to thank the persons from GGSSTP, Ropar helping me in getting to the depth of the working of the thermal plant.

ASE (Training Cell GGSSTP, Ropar.)

I think the knowledge gained by me during this training would greatly help me in becoming a successful Electrical Engineer.

SUBMITTED BY,

KUNDAN KUMAR SINGHINTRODUCTIONElectrical energy occupies top position in the energy table. It can be adopted conveniently in the domestic, industrial and agriculture fields. The availability of electrical energy and its per capita consumption is regarded as an index of national standard of living in the present day civilization. The lack of electricity can hinder the economic as well as social progress of the country.

Next to food, fuel and power are the most important items on which the standard of life depends. Every effort is or has been made to utilize the various natural as well as artificial sources of energy in order to increase the power potential of the nation. The energy in the form of electricity is the most desired since it is the most economical, easy transmission, easy control, cleanliness, greater flexibility, versatile form and can be converted into heat and work as and when desired. The main sources of energy generation in India are solar, wind, tidal, hydro, thermal and nuclear.

Every effort is being made to utilize full potential of energy development available. But if we look at the data available and compare it with the developed countries, we can say that we are still a far to go. The figures below indicate the present sources of energy and their respective division.

TOTAL INSTALLED CAPACITY : 89,798 MW

PEAK DEMAND : 67,500 MW

COAL BASED THERMAL PROJECTS : 65,000 MW

HYDRO PROJECTS : 22,000 MW

NUCLEAR PROJECTS : 2000 MW

WIND POWER : 900 MW

THERMAL POWER GENERATIONIn steam power plants the heat of combustion of fossil fuels (coal, oil or gas) is utilized by the boilers to raise steam at high temperature and pressure. The steam so produced is used in driving the steam turbines or some times steam engines coupled to the generators and thus in generating energy.

Oil and natural gas reserves are small in our country and India has to import large quantities of oil and increasing such imports for power generation is not desirable due to miserable amount of foreign exchange reserves India has. This explains the dependence on coal for generation of electricity in thermal power plants.

Large development in thermal power generation calls for proper choice of site, unit size, coal requirements, transport facility, transmission systems etc. It is normal practice to consider various alternative sites for locating power stations and work out cost comparison to arrive at economically feasible sites.

COAL FOR STEAM POWER PLANTS The main sources of coal in India are Bihar, West Bengal and the central regions. The economic and efficient use of high ash content coal for the thermal plants calls for special treatment. Since 50 to 60% of cost of electricity generation is due to transport cost of coal, so it is imperative that these power plants are located near the washeries.

Main things that are to be kept in mind while selecting coal for modern steam power stations are:

1. Size

2. Moisture

3. Ash

4. Grindability

5. Fusability of ash

6.Calorific value7.Impurities like sulphur, phosphorous, chlorine etSELECTION OF SITE FOR STEAM POWER PLANTS1.SUPPLY OF WATER:A large quantity of water is required in steam power plants. It is required:

(I) To raise the steam in the boiler.

(II) For cooling purposes such as in condensers.

(III) As a carrying medium such as in disposal of ash.

(IV) For drinking purposes.

The efficiency of direct cooled plant is about 0.5% higher than that of the plant in which cooling towers are used. This means a saving of about Rs 7.5 lakhs per year in fuel cost for a 2000 MW station.

2.REQUIREMENT OF LAND:The land is required not only for setting up of the plant but also for other purposes such as staff colonies, coal storage, ash disposal etc. cost of land adds to the final cost of the plant. So it should be available at a reasonable cost. Land should be of good bearing capacity since it has to withstand about 7 Kg per sq. cm. Moreover, land should be reasonably level. It should not be low lying.

3.TRANSPORTATION FACILITY:The land and rail connections should be proper and capable of taking heavy and over dimensioned loads of machines etc.

To carry coal, oil etc which are daily requirements, we need these transport linkages.

4.LABOUR SUPPLIES:Skilled and unskilled labourers should be available at reasonable rates near the site of the plant.

5.ASH DISPOSAL:Ash is the main waste product of the steam power plant. Hence some suitable means for disposal of ash should be applied. Ash can be purchased by building contractors, cement manufactures or it can be used for brick making near the plant site. Otherwise wasteland should be available near the plant site for disposal of ash.

6.DISTANCE FROM THE POPULATED AREA:Since most of the modern generating stations employ pulverized fuel residues and fumes from them are quite harmful. Therefore the site for the plant should be away from the populated area.

7.CLIMATIC CONDITIONS:Climatic conditions of a place play a significant part in economics of capital investment.

WORKING OF THE THERMAL PLANT

Thermal power station burn fuels and use the resultant steam to drive the turbo generator. The object is to convert heat into mechanical energy in the turbine and to convert mechanical energy into electrical energy by rotating magnets inside a set of magnets. The coal brought to the station by means of trains travel from the coal handling plant by conveyor belts to the coal bunkers. From where it is fed to pulverizing mills which grind it to a fine powder. Finely powdered coal mixed with preheated air is blown into the boiler by primary air fan where it burns more like a gas than as a solid with additional amount of air called the secondary air supplied by the secondary draft fan. As the coal has been ground finely the resultant ash is fine powder. Some of its contents bind together to form lumps which fall in ash pits at the bottom of the furnace. The ash mixed with water is then taken to the pits for subsequent disposal. The electrodes charged by high voltage electricity in the electrostatic precipitator trap most of the ash. The dust is then conveyed by water to the disposal area or to the bunkers while the cleaned flue gases pass on through the ID fan to discharge through the chimney. Meanwhile the heat released from the burning of coal has been absorbed by many kms of tubing which line the boiler. Inside these tubes is water, which takes the heat and is converted into steam at high temperature and pressure. This steam at high temperature and pressure is sent to the turbine where it is discharged through the nozzles on to the turbine blades. The energy of the steam striking on the blades makes the turbine to rotate. Coupled to the turbine is the rotor of the generator. So when the turbine rotates the rotor of the generator turns. The rotor is housed inside a stator having heavy coils of copper bars

in which electricity is produced through the movement of magnetic field produced by the rotor. Electricity passes from stator winding to the transformer, which increases its voltage level so that it can be transmitted over the lines to far off places.

The steam, which has given away its energy, is changed back into water in the condenser. Condenser contains many kms of tubing through which cold water is continuously pumped. The steam passing over the tubes continuously loses heat and is rapidly changed back into water. But the two waters i.e. the boiler feed water and cooling water must never mix. Boiler water must be absolutely pure otherwise the tubing of the boiler may get damaged due to the formation of salts inside the tubes due to the presence of different impurities in water.

To condense large quantities of steam huge and continuous volume of water is required. In some power stations same water has to be used again and again because there is not enough water. So the hot water extracts are passed through the cooling towers. The cooling towers are simply concrete shells acting as a huge chimney creating a draught of air. The design of cooling towers is such that a draught of air is created in the upward direction. The water is sprayed at the top of the tower. As it falls down the air flowing in the upward direction cools it. The water is collected in a pond from where the water is recirculated by the pumps to the condenser. Inevitably, however some of the water is taken away by the draught of water in the form of vapours and it is this water with familiar white clouds emerging from the cooling towers.

CONTENTS

1. INTRODUCTION

2. BRIEF HISTORY OF PLANT

3. ELECTROSTATIC PRECIPITATOR

4. DIFFERENT TRANSFORMERS INSTALLED

5. 220 KV SWITCH YARD

6. GENERATOR

7. TURBINE AND ITS AUXILIARIES

8. LT AND HT SWITCHGEAR

1.INTRODUCTION OF THE PLANT

Guru Gobind Singh Super Thermal Plant is built at a site adjacent to Nangal Hydel Channel near Sirsa Aqueduct on a piece of land bounded by sirsa, Mansali and sutlej rivers. It is about 55 Kms from Chandigarh near village Ghanauli on Ropar-Nangal road.

Ever widening gap between power demand and its availability was one of the basic reasons for envisaging the Guru Gobind Singh Super thermal plant for the Punjab State. The historic town of Ropar was selected for this project for easy transportation of coal by railway, availability of cooling water and land. The costly cooling towers have been avoided, as the cooling water temperature is very low. Smt Indira Gandhi laid the foundation stone in December 1980.

The total installed capacity of the power station is 1260 MW with 6 units of 210 MW each in three stages each of two units and the power plant comes in the category of Super Thermal Plants in India.

This plant was awarded Meritorious Productivity Awards and cash rewards by Govt. of India for its good performance during the years: 1985,1986,1987,1990 & 1992.

Special care has been taken to keep the atmosphere pollution free by providing electrostatic precipitators with an efficiency of 99.7%, which extracts ash from the flue gases going out from the boiler. Chimney height has been increased to 220 metros for wide spread of gases at longer distance from the Power Plant to keep the ambient air clean.

TECHNICAL DATA:

1.COST OF THE PLANT: 1417 CRORES

2.DATE OF START: 30 DECEMBER 1980

3.DATE OF SYNCHRONIZATION:

UNIT 126.9.1984

UNIT 229.3.1985

UNIT 331.3.1988

UNIT 429.1.1989

UNIT 529.3.1992

UNIT 630.3.1993

4.DATE OF COMMERCIAL RUNNING:

UNIT 11.01.1985

UNIT 21.10.1985

UNIT 325.09.1988

UNIT 41.08.1989

UNIT 529.09.1992

UNIT 614.12.1993

5.LAND:

MAIN PLANT AREA : 210 ACRES

MARSHALLING YARD: 533 ACRES

RAILWAY SIDING : 65 ACRES

ASH DISPOSAL : 974 ACRES

RESIDENTIAL AREA: 492 ACRES

2274 ACRES

6.RAILWAY TRACK:

LENGTH OF SIDING FROM ROPAR : 8.315 KM

MARSHALLING YARD : 38.330 KM

7.CHIMNEY HEIGHT:

UNIT 1 & 2: 110 MT

UNIT 3 & 4: 220 MT

UNIT 5 & 6: 220 MT

8. COAL:

AVERAGE DAILY REQUIREMENT: 3000 MT/UNIT

TOTAL STORAGE OF COAL : 4,00,000 MT

ASH GENERATED DAILY : 1200 MT/UNIT

9.HEAVY FUEL DAILY REQUIREMENT:

3000 MT/UNIT

10.WATER REQUIREMENT:A) FOR STAGE 1,2,3 : 750 CUSECS

B) CONSUMPTIVE REQUIREMENT : 21.25 CUSECS/UNIT

11.COAL HANDLING PLANT:

A) WAGON TIPPLERS : 5

B) PRIMARY CRUSHERS : 4

C) SECONDARY CRUSHER : 4

D) STACKER CUM RECLAIMER : 3

12.TOTAL ASH HANDLING:

18,00,000 MT/YEAR (VARIABLE)

13. BOILER:

TYPEWATER TUBE SINGLE DRUM WITH REHEATER

CAPACITY680 TONS/HR

MAKEBHEL

STEAM TEMPERATURE540 C

EFFICIENCY87.16%

STEAM PRESSURE155 KGMS/CM2

14.SOOT BLOWERS:

RETRACTABLE SOOT BLOWERS24 NOS

WALL BLOWERS56 NOS

ROTATORY ARM TYPE4 NOS

15.GENERATOR:

MAKEBHEL

TYPETH-210-A

CAPACITY210000 kW

KVA247000 KVA

VOLTAGE15750 VOLTS

AMPERES9050 AMPS

POWER FACTOR0.85 LAGGING

SPEED3000 RPM

1.WATER TREATMENT PLANTWater as it occurs is never Pure, and whatever may be the source, always contains impurities either in solution or in suspension. The determination of these impurities makes analysis of water necessary and removal/control of these impurities make water treatment essential.

1.1 The major impurities of water can be classified in three groups:

i.Non-ionic and Undissolved.

ii.Ionic and Dissolved and

iii.Gaseous.

1.1.1 NON-IONIC IMPURITIES.

These are mainly turbidity, silt, mud, dirt, and other suspended matter, micro-organisms, bacteria and other organic matter, oil and corrosion products.

1.1.2 IONIC AND DISSOLVED IMPURITIES.Any salt which dissolves in water splits into positively charge Cations and negatively charged Anions and since these permit the water to conduct electricity, these salts are called Electrolytes. Some of the most common Cations in water are:-

Calcium, Magnesium, Sodium & Iron and rarely Ammonium and Maganese. These Cations are associated with Anions like Bicarbonates, Carbonates, Hydroxides (The sum of which is termed as Alkalinity) Sulphates, Nitrates and Chlorides of all the dissolved impurities, hardness is the most trouble some and is due to compounds of Calcium and Magnesium.

Sodium salts are highly soluble but can be corrosive if present in large quantities as Sodium Chloride or Sodium Bicarbonate.

Dissolved Silica is another trouble some impurities especially in water fed to Boilers of high temperature & pressure.

1.1.3 GASEOUS IMPURITIES.

Carbon Dioxide and Oxygen are the main gaseous impurities in the waters and causes corrosion in boiler tubes.

1.2 SOURCE OF RAW WATER.

The source of raw water for GGSSTP is Nangal Hydel Channel and its quality

( designed as well as actual ) is as below:

DesignedActual

Turbidity100 ppm5-60 ppm

PH6.9 to 8.1 units8.0 to 8.5 units

Alkalinity60 ppm as Ca CO360-70 ppm

Chlorides45.1 ppm as Ca CO33-10 ppm

Total Hardness90 ppm as Ca CO370-90 ppm

Sulphates44.7 ppm as Ca CO325-35 ppm

Calcium Hardness60 ppm as Ca CO345-60 ppm

Magnesium Hardness30 ppm as Ca CO330-45 Pm

1.3 QUALITY OF WATER USED IN BOILERS.

It depends upon pressure. Generally, the Boiler feed water should not cause:

1.3.1 DEPOSITION OF SCALE ON METAL SURFACE.

Scale is caused by deposition of impurities (Separation of solids) from water on heating surface. During evaporation loose precipitates are formed in Drum. It decreases heat transfer and promotes high tube temperature (rupturing of tubes). This decreases overall efficiency of Boiler. This is due to hardness and Silica salts, present in water.

1.3.2 CORROSION OF BOILER TUBES.This is caused by Acidity, Oxygen, Carbon dioxide or Chlorides. Most serious is dissolved Oxygen in water.

1.4 EXTERNAL WATER TREATMENT.

1.4.1 REMOVAL OF TURBIDITY AND SUSPENDED SOLIDS.

1.4.1.1 CLARIFACATION.

Turbidity comprises of negatively (-vely) charged particles which remains in colloidal form whereas suspended solids are coarse particles and hence settle rapidly. To remove this , a coagulant is added to water to produce positively (+ vely) charged particles which would attract the negatively (-vely) charged particles and thus form dence flocs which settle easily. The equipment performing these duties is called a Clarifloculator (provided in Stage-IInd & IIIrd).

1.4.1.2 FILTRATION.For potable and boiler feed water, passing clarified water through pressure sand filters further reduces this turbidity.

1.4.1.3 CHLORINATION.Chlorination is done to destroy fungis bacteria. This also suppresses biological decomposition of sludge blanket of clarifier.

1.4.2. REMOVAL OF DISSOLVED SOLIDS.This process is called the Demineralization Process and is performed in

DM Plant. This basically consists of 2 units in series, one is called the Cation Exchanger Units and the other Anion Exchanger Unit. The former is filled with Cation Resins which exchange Hydrogen ion in the resin for all the Cations in water. Similarly, Anion Exchanger has Anion resin which exchanges Hydroxyl ion

(OH) for all the Anions in the effluent of Cation exchanger. The result is Dematerialized Water, e.g. let us take dissolved impurity of Calcium Sulphates.

1. Reaction of Cation Exchanger Units

Ca SO4 + H2 ( R ) = Ca ( R ) + H2 SO4Calcium Sulphates + Cation Resin = Calcium salt + Sulphuric acid

2. Reaction in Anion Exchanger Unit

H2 SO4 + R ( OH ) 2 = RSO4 + 2H2 O

Sulphuric + Anion = Sulphates + Water salt

Acid Resin

Therefore, in reaction (1) Ca SO4 has been converted to H2 SO4 and in reaction (2) the same H2 SO4 becomes water. After sometimes, resin become in-effective due to saturation of exchange sides of resins with Ions and these are regenerated with acid and Alkali to bring them back to original conditions.

1.5 D.M. WATER SPECIFICATION.i. pH 6.8 to 7.00

ii. Silica Contents 0.02 ppm (parts per million)

iii. Conductivity 0.2 Micro mho/cm.1.6 INTERNAL WATER TREATMENT.

Regardless of purity of water obtained from external treatment, internal chemical treatment is normally required for complete protection against scale corrosion and foaming.

1.6.1 PHOSPHATE DOSING.

Calcium Carbonate in the drum will react with Tri-sodium phosphate, forming Calcium triphosphate, which can be removed by blow down of drum water. Thus scaling is avoided:

.

1.6.2. HYDRAZINE DOSING.Oxygen in feed water is removed in Deaerator to a considerable degree. The residual Dissolved Oxygen in Deaerator water is removed by dosing Hydrazine (N2H4) at suction of Boiler Feed Pump to nullify effect of dissolved Oxygen.

Hydrazine+ Oxygen=Water + Nitrogen

N2 H4+ O2=2H2O + 2N22N 2H4

=2NH4 + N2Hydrazine=Ammonia + Nitrogen.

Ammonia keeps water Alkaline and N2 being volatile pass through steam cycle unchanged and condenses in condensate and (N2) is not harmful.

Blow-down reduces concentration of solids in Boiler water by removing sludge and concentrated impurities and these are replaced by fresh water. Continuous blow down prevents formation of corrosion, carry over by keeping concentration of salts in Boiler at desired level.

The Water samples in laboratory are tested to achieve Feed\Boiler water

1.7 HARDNESS.

It indicates Calcium and Magnesium salts present in water. Bicarbonates and Carbonates of these salts constitute temporary hardness and Sulphates, Nitrates, Chlorides etc. constitute permanent hardness. These cause scale formation in the Boiler and their removal from water is called softening.

2.PRE AND POST CHEMICAL CLEANING PROCEDURESINTRODUCTION

The chemical cleaning process for the internal surfaces of the Steam Generating section comprises of an initial Alkali boil out followed by an acid-cleaning schedule. The acid pickled surfaces are later passivated to safeguard the exposed metal surface from corrosion attack.

The whole exercise is intended to ensure through cleaning of the water side of the Boiler prior to pressing the Steam Generator into regular operation.

In addition to the above, the Pre-boiler system is also cleaned with a hot Alkaline solution.

2. 1SCOPE OF CLEANING

The scope of cleaning includes a portion of the feed line, entire evaporative system of the Boiler and the Economizer. Super heaters and Reheaters are excluded from the described schedule. During the process, the Super heaters are isolated by providing plugs at the mouth off the take tubes from the Drum.

2.2 PROCESS

Main steps involved in the process are:-

i.Alkali boil out

ii.Acid cleaning

iii.Passivation stage-Ist and Stage-IInd.2.3 TECHNIQUEAlkali boil out at a pressure of 40 Kg/cm2 is carried out using a combination of Trisodium Phosphate (1000 ppm as Na3 PO4, 12 H2 O) and Sodium Carbonate

(500 ppm as Na2 CO3,) this process makes sure of the surface free from any oil/grease contamination. Besides, a portion of the loose muck mainly of Iron Oxide gets flushed out of the system.

Adopting circulation technique, using inhibited (0.1-0.15 Redine 213 spl) Hydrochloric acid (4 to 5% w/v) at 65 oC mixed with 0.5 % Ammonium Biflouride, pickling is carried out. This is followed by a rinse using dematerialized water and a rinse at 55o C using Ammoniated Citric acid of 0.2% with a solution pH maintained at 3.5 - 4.0. Later the system is thoroughly washed with Demineralised Water ensuring that the remnant iron is not more than 25 ppm.

The entire pickled surface is neutralized with 1% solution of Sodium Carbonate at a temperature of 90oC to 95oC. Finally; the cleaned surface is passivated with a solution of dematerialised water containing (a min. of 200 ppm) Hydrazine and Ammonia (pH 10.0).

Prior to the steam blowing operation, the surface is again passivated at a pressure of 40 Kg/cm2, with Hydrazine Ammoniated Dematerialized Water.

2.4EQUIPMENTS FOR CLEANING

Essentially, it consists of a dissolving tank, circulation pumps, connecting pipes and valves to facilities circulation. Nitrogen capping arrangement also forms a part of the system.

The dissolving tank acts as a reservoir for the circulation of various solutions. The pumps force the solution through the Economiser, Drum, and Water walls and Down comers and through the Ring header back to the dissolving tank.

3.GENERAL ASPECT TO BOILER, AIR PREHEATER & SOOT BLOWERS

3.1 GENERAL DESCRIPTION.The steam generator is of radiant, reheat, natural circulation, single drum, dry bottom and semi-outdoor type unit, designed for firing coal as the principal fuel and the HFO oil firing capacity is equivalent to 22.5% boiler MCR. 4 LDO burners are capable for 7.5% boiler MCR heat input. Layout arrangement is of conventional type i.e. with the mills in front of the Boiler. The complete furnace section is of fusion welded wall type, arranged as a gas and pressure tight envelope. The extended side wall section (where reheaters are located) is covered with water cooled fin welded walls.

The super heater steam system has mainly three sections. The LTSH (arranged in the back pass of the unit),the radiant platen super heater ( arranged at the outlet section of the furnace) and the final super heater (arranged after the reheater).

Two numbers super heater desuperheaters are provided in between the LTSH section and the platen super heaters (in the connection links ) for controlling superheated steam temperature over wide load range . The complete back pass of the boiler (up to the economizer) has been covered with steam cooled super heater wall sections.

The complete reheater has been arranged as one section and located in the horizontal pass of boiler in between the radiant platen super heater and final super heater. Two no. Reheater desuperheaters are provided in the cold reheat steam piping at inlet of the reheater for emergency control of the final steam temperature.

The maximum flue gas velocity in the pressure part system is limited to 10-12 m/ sec. at 100% boiler MCR load.

All the headers in the pressure part system are provided with necessary hand holes and hand hole plates arrangements. All headers are located outside the gas path, except for the economizer inlet header, intermediate headers and LTSH inlet header are located in the low gas temperature section.

The complete pressure parts is suspended from the boiler structural steel roof sections and arranged for free expansion downward.3.2. LOW TEMPERATURE SUPERHEATER.

The LTSH section is of the continuous loop, plain tubular, drainable, horizontal, in line spaced type, with steam flow upwards and gas flow downwards arrangements. This section is in two blocks and located above the economizer section, in the back pass of the unit. This convective spaced bearing surface has 120 assemblies, 4 elements per assembly. The outlet section of LTSH alone is arranged vertically.

3.3. RADIANT PLATEN SUPERHEATER.The radiant platen super heater section is of the continuous loop, plain, tubular, non-drainable, vertical, in line tangent tube type, arranged for parallel flow. The platen super heater section assemblies are widely spaced, and located in the radiant zone at the furnace outlet section. The radiant platen-heating surface has 29 assemblies- 7 elements per assembly.

3.4 FINAL (FINISH PENDENT) SUPERHEATER ( FSH ).

Finish pendent super heater (FSH) section, is of spaced type continuous loop, plain tubular, non-drainable, vertical in line spaced type, arranged for parallel flow. This FSH is located in the horizontal pass, after the reheater section. The convective final super heater has 89 assemblies- 2 elements for assembly.

3.5 RE HEATER SYSTEM.The reheater section is a single stage, spaced type, continuous loop, and plain tubular, ondrainable, vertical in line spaced type, arranged for parallel flow. The reheater- front pendant & rear pendant section is located in horizontal pass, in between the Radiant Platen super heater and final super heater section. This convective reheater section has 59 assemblies 6 elements per assembly. The approx. total convective heating surface is 3100 msq. The entire reheater section is suspended from the roof structural steel section.3.6 SUPER HEATER DE SUPERHEATER.For controlling the final super heater steam temperature at rated value, two numbers of spray type de-super heaters are located in the steam connecting links between the LTSH outlet header and platen SH inlet header. This inter stage de-super heaters are of welded type. Spray tubes and liners are provided.

For emergency control of the reheater outlet temperature, two numbers spray type de-super heaters are provided. These are located in the cold reheat piping and used during any abnormal emergency conditions for the steam temperature control. The desuperheaters are of welded type , spray nozzles and liners are provided.

3.7 ECONOMISER SYSTEM.The economizer, a single block unit, is of the continuous 100p plain tubular, drainable, horizontal, in line arrangement with water flow upwards and gas flow downwards. The economizer tubes are suspended from economizer intermediate header, using ladder type supports. The heating surface is 4550msq.An economizer recirculation system is provided, connecting the down comer (near water wall lower ring header) and economizer inlet pipe to ensure required flow through economizer tubes during starting conditions of the unit.

3.8 STEAM DRUM.The steam drum is of the fusion welded construction, fabricated from carbon steel plates. At each end of the drum, a man hole of 406mm dia is provided, arranged to open inwards. The drum is located on the upper front of the unit , the ID of the steam drum are welded type. The drum is equipped with primary turbo separators, secondary corrugated scrubbers and screen dryers, to limit the solids carry over in the steam leaving the drum. All drum internals are of carbon steel construction. The turbo separators ( along with the scrubbers ) and the screen driers are of the removable type. The drum is suspended from boiler roof structures.

3.9 DOWN COMER PIPES.Six (6) Nos. Down Comers are provided, connecting the steam drum and water wall lower ring heater.3.10 WATER WALL SYSTEM.

The water wall system comprises of front wall, rear wall, side walls- all of fusion welded construction. The extended side walls are of fin welded construction.

Furnace Width 13,868 mm

Furnace Depth 10,592 mm

Furnace Volume (Approx.)

5200 m3Furnace affective Projected.

2100 m23.11 RISER PIPES.From the outlet headers of the wall system, the steam water mixture are taken to the steam drum through 118 numbers pipes rolled uprisers.

3.12 WATER WALL / FURNACE DESIGN PRESSURE.The complete furnace walls, and the other steam-cooled walls (in second pass), are strengthened by providing buck stays and tie bars system, to withstand furnace/forces.

3.13 SUPPORTS / SUSPENSION.

The complete circulation system is suspended from boiler roof structures and is arranged for free expansion downwards.

3.14 FURNACE.

The furnace hopper outlet section is provided with an opening of approx. 1100 mm depth, for the full width of the furnace. On each side wall, in the furnace hopper area, one water cooled access door (oval in shape of size 406 x 457 mm) is provided . These openings are provided for taking maintenance cradle parts/ scaffolding sections etc. inside the furnace during maintenance of the furnace.3.15 TILTING TANGENTIAL FIRING SYSTEM.3.15.1 TANGENTIAL FIRING.In the tangential firing system the furnace it self constitutes the burner. Fuel and air are admitted into the furnace through four wind fox assemblies located in the furnace corners. The fuel and air streams from the wind fox nozzles are directed to a firing circle at the center of the furnace. The relative or cyclonic action that is characteristic of this type of firing is most effective in turbulently mixings the burning fuel in a constantly changing air and gas atmosphere.

3.15.2 AIR AND FUEL NOZZLE TILTSThe air and fuel streams are vertically adjustable by means of moveable air deflectors and nozzle tips, which can be tilted upward or downward through a total angle of 60 degrees. However, for the maximum angle of tilt of nozzle tips refer contract assembly drawing. This movement is effected through connecting rods and tilting mechanism in each wind box compartment, all of which are connected to a drive Unit at Each corner operated by automatic control. Provision is given in UCB to know the position of nozzle tips during operation. The tilt drive Units in all four corners operates in unison so that all nozzles have identical tilt positions.

3.16 WIND BOX ASSEMBLYThe fuel firing equipment consists of four-wind box assemblies located in the furnace corners.

Each wind box assembly is divided in its height into number of sections or compartments. The coal compartments (Fuel air compatment0 contain a coal nozzle, the top, bottom and intermediate compartments are used for admission of secondary air (Intermediate air compartments). Combustion air (Secondary air) is admitted to the intermediate air compartments and each fuel compartment (around the fuel nozzle) through sets of louver dampers. Each set of dampers is operated by a damper drive cylinder located at the side of wind box. The drive cylinders at each elevation are operated either remote manually of automatically by the Secondary Air Damper Supervisory system.

Some of the (auxiliary) intermediate air compartments between coal nozzles contain a retractable oil gun.

Eddy plate igniters are installed igniter nozzles are directly adjacent to the oil guns and are mounted at a fixed angle to the fuel nozzles so that the igniter flame crosses the path of the main fuel and air stream.

Retractable High-energy Arc (HEA) igniters (if applicable) are located adjacent to the retractable oil guns. These igniters directly light up the oil guns.

Optical flame scanners are installed in flame scanner guide pipe assemblies in the auxiliary air compartments. The scanners pick-up visible light given off by the flame and there by prove the flame.

4. BOILER AIR AND GAS SCHEMES

AIR IS REQUIRED IN BOILER MAINLY FOR THE FOLLOWING PURPOSE AT GGSSTP ROPAR.

i.For combustion of fuel in the furnace, called secondary Air.

ii.For drying and transportation of pulverized coal to the furnace from the mill , called primary Air.

4.1. COMBUSTION SECONDARY AIRThe secondary air is supplied by two forced Draft Fans. The rating of FD fans is given below:-The secondary air for combustion is preheated upto 317oC by means of regenerative air-heater (Rotary Air Heater). The air heater air out ducts are interconnected to provide a balanced air flow to the furnace and to make it possible to operate the unit at reduced load if one fan is out of service. Distribution of secondary air to the Wind Box compartments is controlled by the secondary Air dampers. The steam coil air reheaters (SCAPH) one each at the outlet of F.D. Fans &before RAH has been provided to avoid the corrosion of RAH by increasing the temperature of secondary air entering the RAH when the Boiler is initially Lighted-up .

SR No.PARTICULARS.SUPPLIERS DATA.

1.EquipmentForced draft fan.

2.Type of operationContinuous

3.No. of fansTwo Per Boiler

4.Medium handledAtmospheric Air

5.Fan OrientationHorizontal delivery and vertical suction

6.LocationGround Floor

7.Type of FanAxial type

8.Capacity110.m3 /sec.

9.Total head developed520 mm wc

10Temp. of medium500C

11.Fan speed1480 RPM.

12.Motor Rating750 KW, 6.6KV,1480RPM.

13.Motor TypeSQ,CAGE Induction

14.Fan bearings lubricationForced oil lub.

15.Motor bearing lub.Grease.

16.Fan RegulationVariable pitch fan

17Fan Weight8570 kg.

4.2 CONVEYING AND DRYING OF PULVERISED COAL

The air used to dry and transport the pulverised coal is referred to as primary air. Two primary air fans supply the air to the pulverisers. The specifications of PA fans are given below:-

SR No.PARTICULARS.SUPPLIERS DATA.

1.EquipmentPA Fan

2.Type of operationContinuous

3.No. of fansTwo per Boiler.

4.Medium handledAtmospheric air.

5.Location.Ground Floor.

6.OrientationVertical Suction Bottom Horizontal delivery

7.Fan capacity70m 3/sec.

8.Total head developed1210mmwc

9.Fan speed1435RPM

10Temp. of medium500C.

11.Motor rating1250 KW, 6.6 KV, 1480RPM

12.Fan bearing lub.Forced oil lub.

13.Motor bearing lub.Grease

14.Type of fan regulationInlet Damper control

To ensure proper drying in the Pulverisers, both hot and cold air must be available. Therefore, a Portion of the air from the primary air fans passes through the air pre-heater . The primary air fan inlet vanes modulate to Maintain a predetermined pressure in the hot air duct.

The air flow and mill outlet temp. can be controlled by simultaneous operation of hot and Cold air dampers. If a primary air fan is not available for service, it must be isolated from the system by its closing its control and outlet shut off dampers. The Primary Air Path has been shown in Figure no. 13.5. HEAT IGNITOR

5.1 SYSTEM DESCRIPTION.

The high energy Ignitor is designed to ignite a variety of fuel ranging from high speed diesel to Heavy Fuel Oil (HFO) or Heavy Petroleum Stock (HPS). The equipment gives a high intensity electrical spark which immediately ignites the oil particles surrounding the spark, thus creating a flame pocket in the oil spray. The flame propagates into the oil spray from this pocket giving a successful ignition.

The Ignitor works in combination with the discriminating flame scanner which is capable of sensing the associated flame only. The discriminating flame scanner senses the flame immediately after the ignition and permits the firing to continue.

The major components of HEA Ignitor are:-

1. Ignitor Exciter

2. Flexible cable

3. Spark rod

4. Replaceable firing tip

5. Spark tip

6. Guide pipe

1.1Specifications.Input Voltage -110V AC + 10%

- 15%

50 + 5 hertz

Out put voltage 2500 + 150 V.DC

5.2 THEORY OPERATION.

Application of 100-130 volts AC, 50/60 Hz to the primary side of the exciter induces a high voltages on secondary of the power transformer. The high voltage generated in the secondary of the power transformer is rectified in the double circuit by the action of the two solid state rectifiers and double capacitors, so that with each change, in the polarity a pulse of DC voltage reaches the storages capacitor. The resister and inductor in the double circuit serve as limiters.

When this voltage reaches the predetermined level for which the spark gap in the discharge tube has been calibrated, the gap will ionize. Current will flow from the storage capacitor(s) through the discharge tube, the center conductor of output lead to the firing tip, returning to storage capacitor through the output load. When the energy is dissipated at the ignitor tip, the storage capacitors will be recharged.

Bleeder resisters are provided to dissipate any residual charge on the storage capacitors between cycles. Resisters in the output circuit provide a discharge patch for storage capacitor energy in the event that the ignitor fails to fire, or the unit is subjected to open circuit operation.

6.COAL HANDLING PLANTCoal handling Plant has the following basic functions to perform:

1. Unloading of coal wagons.

2. Reclaiming of crushed and uncrushed coal.

3. Coal crushing.

4. Removal of unwanted particular from the coal.

5. Coal feeding to the raw coalbunkers of running units.

6.1 WAGON TIPPLER:

Wagons tippler- theseare5 in no are used for unloading the coal wagon tippler consists of rail table, tracks, pits holding beam. It has a pit. In pit there is suspension. At the top of wagon tippler, there is holding beam for holding the wagon. The wagon is unloaded on grating. The rail table is turned at an angle of 135. With the help of A.C. motor whose H.P. is 95. The whole process is mechanical. Shunters are used for placing the wagons on rail table. The whole wagon get unload in 4 minutes (app.). The weight of wagon is measured with the help of electronics motion wave Bridge. Approximately weight of wagon is 82 ton including weight of wagon. Each wagon contains 58 tons of coal. The types of wagon are n-type and c-type. Shunter or loco have the H.P. of 450 H.P. and 650 H.P. During measuring of wagon, the speed of train should be 5Km/hr-10Km/hr and weight is measured with electronics motion wave bridge. Coal is stored in crushed and uncrushed form uncrushed form, raw coal pile area where uncrushed coal is stocked. Crushed coal at stacker cum reclaimer. Stone pickers are stationed at primary and secondary crushers to remove the stones the iron particles are removed by magnets. Magnets used are of permanent magnet or cross belt suspended magnets. Permanent magnets are on the conveyer belts used to lift the particles and particles are removed. Cross belt suspended magnets are surrounded the belt in circular motion it has iron bars comes near the belt and become magnet and picks up the iron particles. When it moves away, it demagnetizes and removes the particles.

MUTH- (manual unloading track hopper) when there is fault in wagon tippler, it is used. Coal is unloaded manually on grating.

SCR- (stacker cum reclaimer) when coal size is reduced to 25mm. The coal is in large quantity, then crushed coal is stacked and when necessary is reclaimed.

ERH- (emergency reclaimer hopper) when there is emergency, coal is reclaimed.

6.2 MANUAL UNLOADING:

Manual unloading is done by the labor itself by using the suitable equipments. The wagon capacity is 58 tons and it itself weights 2 tons. The capacity of bunker hall is 660 tons, which is sufficient for 22 hours. The raw coal has a size of the order of 500 mm approx. This coal is sent to the primary crusher on conveyor belts and reduced to a size of 125 mm. This coal from primary crusher is sent to secondary crusher. Secondary crusher further reduces the size of the coal to 25mm. This coal from secondary crusher is sent to coal mills on the conveyor belts. CHP also has stackers and reclaimers.

7 Coal pulverizing systemAt G.G.S.S.T.P Bowl mills have been installed for pulverizing the raw coal. The coal is reduced to the form of talcum powder. Coal of size 25mm is in raw bunkers from CHP. Fineness of coal is measured as the percentage of coal that will pass through a lost sleeve then it has the desired fineness. Designed mill capacity is 39.7-tons/hr. but it depends on the hard groove grind ability index (HGI), the moisture content of coal and fineness requirement of pulverized coal.

Coal with a bulk density 71.2T/m3 should be rejected.

(Designed air flow/mill: - 53.89 tons/hr

(Mill outlet temperature: - 75( to 80(C

(Mill differential pressure: - 200 to 225 mm of WC

(Mill no load current: - 34 Amp

(Mill full load current: - 46 Amp7.1 BOWL MILL

Broadly the Bowl Mill can be divided into four parts:

7.1.1 MILL BASEThis is the lowest position of the mill and it contains mill drive system i.e. worm shaft, worm gear, vertical shaft, oil cooler as main parts. The gear hosing is always filled with lubrication oil before the pulverizer is put into operation . Level of the oil can be checked from the oil level gauge provided on the mill base. Correct level is indicated only while the mill is idle. For cooling the oil while mill is in operation , tube type water coolers have been installed in the Gear Housing.

7.1.2 MILL SIDEThis portion is just above the mill base and it contains mill side liners, scrapper assembly and Tramp iron spout discharge arrangement & vane assembly. Heated primary air enters the mill side housing below the Bowl . Any tramp iron etc. drops in this portion and is scrapped to the Tramp iron discharged spout.

7.1.3 SEPARATOR BODY ASSEMBLY.

This portion is just above the mill side housing and this is the portion where coal is pulverized. Main parts of this assembly are Bowl , Journal assembly , Grinding Roll Assembly , Bowl segment liners, Inner cone, Classifier Assembly , Separator Body Liner Assembly and Center Feed Pipe . The Grinding Rolls do not touch the Bowl if the mill is empty. When the raw coal from center feed pipe comes in between the Grinding Rolls and revolerving bowl , it causes the roll to turn and thus , the coal gets pulverized.

The roller journals is lubricated by means of a self contained circulating system . Seal air is supplied to roller journal shaft to prevent coal dust from entering the roller journal bearings.

7.1.4 MILL OUTLET ASSEMBLYThis portion contains classifier venturi and deflector regulator. Mill discharge valve assembly is connected at the top of this portion from where the pulverized coal is sent to each of four coal nozzles at one elevation .

7.2 OPERATIONThe coal is fed through center feed pipe into the revolving Bowl where it travels towards outer perimeter of Bowl due to centrifugal force. Thus, the coal comes below the roll and gets pulverized. Hot air entering the mill side housing below the bowl passes upward around the Bowl. It picks up the pulverized coal and passes through deflector openings at the top of inner cone and goes out through the venturi to mill outlet part assembly. The deflector blades impart a spinning action to coal air mixture and thus, oversize coal is sent back to the Bowl through the inner cone for additional grinding. Any tramp iron or other foreign material which is difficult to grind drops out through the air stream to the lower part of the mill side housing where it is swept to the tramp iron spout by the two scrappers attached to the bowl mill skirt.

7.3 OPERATING PARAMETERS AIR FLOW AND MILL OUT LET TEMPERATURE.

Hot air is supplied to the mill by Primary Air Fan which is heated in the Air Pre heaters. Of course, the temperature of the air can be controlled by mixing cold air from cold primary air duct.

a. The designed airflow per mill is 53.89 tones/hr.

b. Recommended mill outlet temperature is 75oC to 80 oC

c. Lower air flow and mill outlet temperature below 60oC may not dry the coal sufficiently, and may cause chocking.

d. Outlet temperature must not exceed 95oC in any case as the high temperature may lead to mill fires.

e. Higher airflow mill cause excess wear and upset the classifier etc.

The airflow and mill outlet temperature can be controlled by simultaneous operation of hot and cold air dampers.

7.4 PULVERIZED FUEL FINENESSFineness of coal is measured as the % of the coal that will pass through a test sieve, if 70% of coal passes through 200-mesh sieve then it has the desired fineness. The fineness can be controlled by operating the classifier vanes. It must be remembered that operating the mills at higher fineness increases the wear rate and reduces the capacity of the mill.

7.5 MILL CAPACITY.Designed mill capacity is 39.7 tonnes/hr. But it depends on the hard groove grind ability index, the moisture content of coal and fineness requirement of pulverized coal.

8. BOILER FEED PUMPBoiler Feed Pump is very import auxiliary of the power house . It has to take supply of water from the Deaerator, and supply it to Boiler drum against the positive drum pressure. The supply of the water to the Boiler drum is regulated by the Feed control station and scoop tube.

a. Feed control station has:

i.Main Feed Line (100%)

ii.By pass Line (100%)

iii.Low load Line (30%)

b.Scoop tube variation is from 30% to 100%30% is the minimum scoop tube position.

8.1 IMPORTANT OBSERVATIONS IN CASE OF DEAERATOR.

i.Minimum level (+) 300 mm.

ii.Deaerator pressure:The Deaerator pressure is to be maintained according to Feed water temperature as per following table:-

FEED WATER TEMPERATURE DEAERATOR PRESSURE.

110o C0.5 kg/cm2

120 o C1.0 kg/cm2

130 o C2.0 kg/cm2

140 o C3.0 kg/cm2

150 o C4.0 kg/cm2

160oC5.5kg/cm2

There is minimum recirculation line which is meant to keep the minimum flow of water to be maintained. There is a recirculation valve (pneumatic valve) which opens when the flow of water in the line falls to 100 Tons/hr

There is one manual valve also in the recirculation line. It is to be kept open all the time & locked. The pneumatic valve closes when feed flow is high of the order of 225 Tons/Hr.

There are three Boiler Feed Pumps available in a unit. But two no are sufficient to run the Unit. When on full load , the third is to be kept on auto stand by .

8.2 TRIPPING OF BFP.

1.BFP running and discharge pressure low less than 40 kg/cm2 with time delay of 15secs.2.BFP running & suction flow very low(below 80 T/hour ) time delay 15 secs.3.Suction flow very high (480 T/hour and above with time delay of 10 secs.

4.Deaerator level very low (control from each of very low level switch L&R in parallel with time delay of 1.5 2 secs.)5.Motor DE/NDE Bearing temperature very high (setting 90oC).6.Working oil temperature very high (130 oC).7.Hydraulic coupling bearing No.-6 only (95oC) temperature very high.8.Lub. oil pressure very low below 0.8 kg/cm2 + 10 secs. time delay.8. Booster pump suction pressure very low (below 1.9 kg. /cm2 +time delay 6 secs.)9 BOILER AND ITS AUXILIARYS GENERAL DESCRIPTION:

BOILER

The steam generator is of radiant, reheat, natural circulation, single drum, dry bottom and semi-outdoor type unit designed for firing coal as the principle fuel and the HFO oil firing capacity is equivalent to 22.5% boiler MCR. Four LDO burners are capable for 7.5% boiler MCR heat input. A layout arrangement is of conventional type that is with the mills in front of the boiler. The complete furnace section is of fusion welded wall type, arranged as a gas and pressure tight envelop. The extended sidewall section (where re-heaters are located) is covered with water-cooled fin welded walls.

The super-heater steam system has mainly three sections:

1) LTSH (arranged in the back pass of the unit).

2) Radiant Platen Super-heater (arranged in the outlet section of the furnace).

3) Final Super Heater (arranged after the re-heater).

Two nos. super heater de super-heater are provided in between the LTSH section and the Platen Super-heater for controlling superheated steam temperature over wide load range. The complete back pass of the boiler has been covered with steam cooled super-heater wall sections.

The complete re-heater has been arranged as one section and located in the horizontal pass of the boiler in between the radiant platen super-heater and final super heater. Two nos. re-heater de super-heater are provided in the cold reheat steam piping at the inlet of the re-heater for emergency control of final reheat of the steam temperature. The maximum flue gas velocity in the pressure part system is limited to 10 -12 m/sec at 100% boiler MCR load. All the headers in the pressure part system are provided with necessary hand holes and hand holes plates arrangement. All headers are located outside the gas path, except for the economizer inlet header; intermediate headers and LTSH inlet header are located in the low gas temperature section.

The complete pressure parts are suspended from the boiler structural steel roof sections and arranged for free expansion downwards.

9.1 LOW TEMPERATURE SUPER-HEATER:

The LTSH section is of the continues loops, plain tubular, drainable, horizontal, in line spaced type, with steam flow upwards and gas flow downwards arrangements. This section is divided in two blocks and located above the economizer section; in the back pass of the unit. This convective spaced bearing surface has 120 assemblies, four elements per assembly. The outlet section of LTSH alone is arranged vertically.

9.2 RADIANT PLATEN SUPER-HEATER:

The Radiant Platen Super-heater section is of the continuous loop, plain, tabular and non-drainable vertical in line tangent tube type arranged for parallel flow. The platen super-heater section assemblies are widely spaced and located in the radiant zone as the furnace outlet section. The radiant platen-heating surface has 29 assemblies, 7 elements per assembly.

9.3 FINAL SUPER-HEATER:

Finish pendant super-heater section is of spaced type, continuous loop, and plain, tabular, non-drainable, vertical in line spaced type, and arranged for parallel flow. This FSH is located in the horizontal pass, after the re-heater section. The convective final super-heater has 89 assemblies, two elements per assembly.

9.4 RE-HEATER SYSTEM:

The re-heater section is of single stage, spaced type, continuous loop, and plain tubular, non-drainable, vertically in line spaced type arrangement for a parallel flow. The re-heater front pendant and rear pendant section is located in the horizontal pass, in between the radiant platen super-heater and final super-heater section. This convective re-heater section has 59 assemblies, 6 elements per assembly. The approx. total convective heating surface is 1300 m2. The entire re-heater section is suspended from the roof structure steel sections.

9.5 SUPER-HEATER DE-SUPER-HEATER:

For controlling the final super-heater temperature at the rated value, two no. of spray type de-super-heater are located in the steam connecting links between the LTSH outlet header and platen super-heater inlet header. For emergency control of the re- heater outlet temperature, two no. spray type de-super-heater are provided. These are located in the cold reheat piping and are used during any abnormal conditions for the steam temperature control. The de-super-heater are of welded type, spray nozzles and liners are provided.

9.6 ECONOMIZER SYSTEM:

The economizer is a single block unit and is of continuous 100% plain tubular, drainable, horizontal in line arrangement with water flow upwards and gas flow downwards. The economizer tubes are suspended from economizer intermediate header, using ladder type support. The heating surface is of 4550 m2 and economizer re-circulating system is provided, connecting the down comer and economizer inlet pipe to ensure the required flow through economizer tubes during starting conditions of the unit.9.7 STEAM DRUM:

The steam drum is of fusion-welded construction fabricated from carbon steel plates. At each end of the drum, a manhole of 406 mm diameter is provided, arranged to open inwards. The drum is located on the upper front of the unit; the body of the steam drum is welded type. The drum is equipped with primary turbo separators; secondary corrugated scrubbers and screen dryers, to limit the solids carry over in the steam leaving the drum. All drum internals are of carbon steel construction. The turbo separator along with the scrubbers and the screen dryers of removable type. The drum is suspended from boiler roof structure.

9.8 DOWN COMER PIPES:

Six number down comers are provided, connecting the steam drum and water wall lower ring header.

9.9 WATER WALL SYSTEM:

The water wall system comprises of front wall rear wall, sidewalls and is fusion-welded construction. The extended sided walls are of fine welded construction.

Furnace Width13868 mm.

Furnace Depth10592mm.

Furnace Volume5200m3.

9.10 RISER PIPES:From the outlet headers of the water wall system, the steam water mixture are taken to the steam drum through 118 no of pipes rolled upstairs.

9.11 WATER WALL/FURNACE DESIGN PRESSURE:

The complete furnace walls and the other steam cooled walls are strengthened by providing buck stay and tie bars system, to with stand furnace pressure/forces.

9.12 SUPPORTS/SUSPENSION:

The complete circulation system is suspended from boiler roof structures and is arranged for free expansion downwards.

9.13 FURNACE:

The furnace hoppers outlet section is provided with an opening of approx 1100 mm depth, for the full width of the furnace. On each sidewall, in the furnace hopper area, one water-cooled access door is provided. These openings are provided for taking maintenance cradle parts/scaffolding sections etc, inside the furnace during maintenance of the furnace.

9.14 SPECIAL FITTINGS AND VALVES:

Access doors, feed water valves, gauge glasses and safety valves etc are included.

9.15 MAJOR AUXILIARIES:

Following are the major auxiliaries of boiler at GGSSTP:

1. I.D.FAN

3 No. Including one stand by.

2. F.D.FAN

2 No.

3. P.A.FAN

2 No.

4. MILLING CIRCUIT

6 No.

5. ROTARY AIR HEATERS

2 No.

6. ELECTROSTATIC PRECIPATOR28 No.

7. ASH HANDLING PLANT

8. FUEL OIL SYSTEM

9.16 BOILER PARAMETERS:

1. Super heated outlet steam flow

690 T/Hr.

2. Steam Pressure at SH outlet

155 Kg/cm2.

3. Steam temperature at SH outlet

540(C.

4. Re-heat outlet steam flow

597.5 T/Hr.

5. Steam pressure at RH inlet

37.6 Kg/cm2.

6. Steam pressure at RH outlet

36.1 Kg/cm2.

7. Steam temperature at RH inlet

342(C.

8. Steam temperature at RH outlet

540(C.

9. Feed water temperature entering economizer243(C.

10. Ambient Air temperature

40(C.

9.17 SOOT BLOWERS:

Soot blowers have been provided with cleaning and soot blowing the water walls, super-heaters and re-heaters tubes for efficient heat transfer in both radiation and convection zones. Soot blowers are operated as often as necessary to keep the external surface clean. A high economizer exit gas temperature that is 346(C normal or erratic steam temperature control action may be an indication of need for blowing off soot i.e. 140(C at chimney. Recording and comparing the exit gas temperature at various loads and furnace condition can establish a proper soot-blowing schedule. The requirement of main/HRH steam temperature control system can be used as an indication of the fouling in the furnace SH and RH since DESH spray quantity, fuel nozzle tilt movement and gas re-circulation quantity reflect the changes in the tube surface cleanliness.

Abnormal low steam temperature may be due to a fouled SH/RH externally or internally and abnormal high steam temperature may be due to a dirty furnace. If the steam temperature is too low, the furnace walls should be cleaned only as necessary, in steps using one wall blower operating for a period and using another wall blower at another wall, cleaning all the furnace walls at once may give an extremely low steam temperature. If the steam temperature is generally too high, the furnace should be cleaned thoroughly. As slag develops in the furnace, the heat absorption rate of the furnace will be decreased considerably and steam temperature and over all performance of the unit will be affected. There are two types of soot blowers in the furnace of 210 MW units.

9.18 TANGENTIAL FIRING SYSTEM:

In the tangential firing system the furnace itself constitutes the burner. Fuel and air are admitted into the furnace through four wind-box assemblies located in the furnace corners. The fuel and air stream from the wind-box nozzles are directed to a firing circle at the center of the furnace. The rotating action that is a characteristic of this type of firing is most affective in turbulently mixing the burning fuel in a constantly changing air and gas atmosphere.

9.19 AIR NOZZLES AND FUEL NOZZLE TILTS:

Air and fuel streams are vertically adjustable by means of moveable air deflectors and nozzle tips, which can be tilted upward or downward through a total angle of 60(. This movement is affected through connecting roads and tilting mechanism in each wind-box compartment, all of which are connected to a device unit at each corner operated by automatic control. Provision is given in UCB to note the position of nozzle tips during operation. The tilt drive units in all four corners operate in union so that all nozzles have identical tilt positions.

9.20 WIND-BOX ASSEMBLY:

The fuel firing equipment consists of four wind-box assemblies located in the furnace corners. Each wind-box assembly is divided in its height into a number of sections. The coal compartment contain a coal nozzle, the top, bottom and intermediate compartments are used for admission of secondary air. Combustion air is admitted to the intermediate air compartments and each fuel compartments through sets of louver dampers. A damper drive cylinder located at the side of wind-box operates each set of dampers. The drive cylinders at each elevation are operated either remote manually or automatically by the secondary air dampers. Some of the intermediate air compartments between coal nozzles contain a retraceable oil gun. Optical flame scanners are installed in flame scanner guide pipe assemblies in the auxiliary air compartment. The scanners pick up visible light given off by the flame and thereby prove the flame.

9.21 GENERAL COMBUSTION OF PULVERIZED COAL:

The system for direct firing of pulverized coal utilizes bowel mills to pulverize the coal and tilting tangentially wind-box to admit the pulverized coal together with the air required for combustion to the furnace. As crushed coal is fed to each pulverizer by its feeder primary air is supplied from the primary air fan. The primary air-dries the coal, as it is being pulverized and transports the pulverized coal through pulverized coal piping system to the coal nozzles in the wind-box assemblies. A portion of the primary air is pre heated in the air heater. The hot and cold primary air is mixed proportionally prior to admission to the pulverizer to provide the required drying as indicated by the pulverizer outlet temperature. The total primary airflow may constitute from approx. 20 30% of the total unit combustion air requirement.

The pulverized coal and air discharged from the coal nozzles is directed towards the corner of the furnace to form a firing circuit. Fully pre heated secondary air for combustion enters the furnace around the coal nozzles and through the auxiliary air compartments directly adjacent to the coal nozzle compartments. The pulverized coal and air streams entering the furnace are initially ignited by a suitable source at the nozzle exit. A large portion of the ash is carried out of the furnace with the flue gases the remainder is discharged through the furnace bottom into the ash pit.

9.22 COMBUSTION OF PULVERIZED COAL:

The velocity of the primary air and coal mixture with the fuel nozzle tip exceeds the speed of flame propagation. Upon leaving the nozzle tip the stream of coal and air rapidly spreads out with a corresponding decrease in velocity especially at the outer fringes where eddies form as mixture with the secondary air. Here flame propagation and fuel speeds equalize, resulting in ignition. The speed on which the air and coal mixture ignites after leaving the wind-box nozzles depends large, on the amount of volatile matter in the fuel.

9.23 HEAT IGNITER:

The high-energy igniter is designed to ignite a variety of fuel ranging from high-speed diesel to heavy oil or heavy petroleum stock (HPS). The equipment gives a high intensity electrical spark, which immediately ignites the oil particles surrounding the spark, thus creating a flame pocket in the oil spray. The flame propagates into the oil spray from this pocket giving a successful ignition. The igniter works in combination with the discriminating flame scanner, which is capable of sensing the associated flame only. The discriminating flame scanner senses the flame immediately after the ignition and permits the firing to continue.

The major components of HEA igniter are:

1. IGNITER EXCITER.

2. FLEXIBLE CABLE.

3. SPARK ROD.

4. REPLACEABLE FIRING TIP.

5. SPARK TIP.

6. GUIDE PIPE TIP.

10.ELECTROSTATIC PRECIPITATOR In India coal is widely used to generate power. The exhaust gases from the furnace contains large amount of smoke and dust. If these gases are emitted directly into the atmosphere, it will cause great environmental problems. So it is necessary to extract this dust and smoke before emitting the exhaust gases into the atmosphere.

There are various methods of extracting dust but electrostatic precipitator is the most widely used. It is due to its high efficiency of about 99% and less maintenance.

Its various other advantages are as follows:

1.Ability to treat large volume of gases at high temperature.

2.Ability to cope with the corrosive atmosphere.

3.It offers low resistance to the flow of gases.

WORKING PRINCIPLE:

The electrostatic precipitator utilizes electrostatic forces to separate dust particles from the gases to be cleaned. The gas is passed through a chamber, which contains steel plates (vertical) curtains. These steel curtains divide the chamber into number of parallel paths. The framework is held in place by four insulators, which insulate it electrically from all parts, which are grounded.

A high voltage direct current is connected between the framework and the ground, thereby creating strong electric field between the wires in the framework and the curtains. Strong electric field creates corona discharge along the wire. The ionized gas produces positive and negative ions.

In the chamber plates are positively charged whereas the wire is negatively charged. Positive ions are attracted towards the wire whereas the negative ions are attracted towards the plates. On their way towards the curtains negative ions strike the dust particles and make them negatively charged. Thus ash is collected on the steel curtain.

The whole process is divided into the following parts:

1.CORONA GENERATION.

2.PARTICLE CHARGING.

3.PARTICLE COLLECTION

4.PARTICLE REMOVAL.

10.1 CORONA GENERATION:

It is basically a gas discharge phenomenon associated with the ionization of gas molecules by electron collision in a region of high electric field strength. It requires non- uniform electric field, which is obtained by wire as one electrode and cylinder or plate as other. The corona process is initiated by the presence of electrons in the electric field near the wire. These electrons are accelerated to high velocities and possess sufficient energy so that on impact with the gas molecules in the region they emit orbital electrons from the gas molecules. These electrons also accelerate and enter into ionization. In this region of corona discharge, there are free electrons and positive ions. The behavior of charged particles depend upon the polarity of the electrodes. Both positive and negative coronas are used in industrial gas cleaning.

In case of negative corona, positive ions generated are attracted towards the negative electrode wire and the electrons towards the collecting plates. Beyond the corona glow region, the electric field diminishes rapidly and if electronegative gases are present, electrons will be captured by the gas molecules. On impact the negative ions thus generated moves towards the collecting electrodes and serves as the principle means of charging dust.

Temperature and pressure influence the generation of corona by changing the gas density. In the avalanche process, the time available for accelerating the electrons during the collision is a function of gas density. With the increased molecular spacing, higher velocities can be achieved between the collisions. Thus energy can be achieved with low field and for low gas densities. Increased molecular spacing results in penetration of free electrons further into the inter electrode region before captured to form negative ions. This increases the mobility in the inter electrode space and hence higher current.

Corona is affected by dust on emitter and collector electrodes. It alters the electric field and the sparking condition.

10.2 PARTICLE CHARGING

There are two physical mechanisms by which gas ions charge the dust particles. The electric field causes localization of field so that the electric field intersects the particles. The ion which move along the path of maximum voltage gradient, intercepts the particle thus net charge flow through the particle. The ion is held with the dust particle by induced image charge force between the ion and the dust particle. As additional ions are held with the dust particle, it becomes charged to a value sufficient to divert the electric field from the particle. For small particles field dependent charge mechanism is less important and collision between the gas ion and the particle is governed primarily by the thermal motion of the ions.Rate of charging depends upon:

10.2.1FIELD STRENGTH:

Higher the field strength more is the charging.

1. Concentration of uncharged dust in the section.

10.3 PARTICLE COLLECTION:

Forces acting on the charged particles are gravitational, inertial, electrical and aerodynamical. Electrical and aerodynamical are more important.

If the particle is suspended in a laminar gas flow stream, charge will act on the particle in the direction of the collecting electrode. This force is opposite to the viscous drag force of the gases. In a short time particle would reach the terminal velocity at which electrical and viscous drag forces are equal. This is called the migration velocity. The other force is the aerodynamic force by the gas stream. The motion is along the line defined by the vector sum of these two forces. Under laminar flow all particles are collected at given precipitator length. But this is never achieved. The turbulent gas flow causes particles to flow in random path through the precipitator.

10.4 REMOVAL:

Dust collected must be removed. This is done by causing the liquid to flow down the collector electrode or by rapping mechanism. Rapping is done periodically. The success of the rapping system depends upon accumulation of sufficient thickness of material on the plate. The acceleration required to remove the collected dust vary with the property of the dust and gas stream. Reentrainment of dust during rapping is evidenced by the increased dust loading at the exit. To minimize this effect, only small section of the precipitator is rapped at a time.

10.5 RAPPING MECHANISM:

It consists of a geared motor which moves a long shaft placed near the support of the collector electrode. The shaft is provided with hammers. When shaft moves, hammers fall on the supports and hence dust is removed from the plates. For the collecting electrodes this system is provided at the bottom of the casing and for emitting system it is provided at the centre.

At the exit of hoppers heaters are provided. When we start the precipitator. Hoppers are at normal temperature but the ash collected is very hot. So there is a chance of ash deposit at the exit of the hopper thus causing problem of removing the ash. To avoid this heaters are provided which increase the temperature at the exit point of the hopper thus avoiding any undue accumulation of ash at starting.

The whole precipitator is divided into two parts:

10.6 ELECTRICAL SYSTEM:

Transformer rectifier unit, auxiliary control panel, safety inter locks and field equipments.

10.7 MECHANICAL SYSTEM:

Casing, hopper, gas distribution system, collecting system and rapping mechanism.

In precipitator we require high voltage dc supply to generate sufficient electric field.

Two main equipments which are used to generate and control high voltage are:

1. High voltage transformer rectifier

2. Electronic controllerElectronic controller provides control ac voltage through thyristors and associated controls. The high voltage transformer rectifier converts this controlled ac into high voltage dc, which is supplied across the electrode.

SPECIFICATIONS:

INCOMING SUPPLY415V, +-10%, 1 PHASE,

50HZ+-5%

CURRENT DRAWN FROM SUPPLY167 AMP A.C FOR 800MA D.C

I/P VOLTAGE TO PRIMARY OF HVR AFTER A.C REACTOR0 TO 373.5 VOLTS A.C

OUTPUT VOLTAGE FROM THE THYRISTOR0-415V RMS

CONTINUOUSLY ADJUSTABLE

DC OUTPUT OF HVR0-70 kV(PEAK)

DC OUTPUT CURRENT800 MA(MAX AVG)

FORM FACTOR1.4 (MAX)

OPERATING TEMPERATURE-5 TO 50 C

MAX ARCING CURRENT3 ANP(PEAK)

The transformer rectifier unit consists of an oil- immersed step up transformer, ac reactor, high voltage rectifier, high frequency choke and other measuring and protection components.

The transformer is a single phase, 60 KVA, 373/53570v, 50 Hz with ONAN cooling. It is double wound core type.

Ac reactor is provided for limiting the primary current in an event of flash over or short circuit on the dc side. It also improves the form factor. The reactor is specially designed to provide linear inductance up to 300% of the rated current. Its inductance is about 2 mH.

High frequency dc choke is connected on the dc side. It provides high impedance to high frequency currents that may be generated due to arcing. It also provides limiting effect on di/dt for the rectifier diodes. Inductance is about 2 mH at 100 kHz.

High voltage rectifiers are made up of specially designed diodes. They are designed to with stand voltage and current repetitive peaks. The high voltage rectifier consists of an integrated series connection of avalanche diodes. The diodes are assembled on a printed circuit board and are embedded in epoxy resin partially and body of the diode is kept above the epoxy resin for oil cooling. Seven modules are connected in series to form an arm for single phase. Such four arms are assembled along with bus bar termination for ac and dc connections of full wave single-phase bridge rectifiers. Complete assembly is fitted inside the oil filled transformer tank.

11.GENERATOR

MAXIMUM CONTINUOUS KVA RATING247000 KVA

MAXIMUM CONTINUOUS kW RATING210000 kW

RATED TERMINAL VOLTAGE15750 V

RATED STATOR CURRENT9050 A

RATED POWER FACTOR0.85 LAG

EXCITATION CURRENT AT MCR CONDITION2600 A

EXCITATION VOLTAGE AT MCR CONDITION310 V

RATED SPEED3000 RPM

RATED FREQUENCY50 HZ

EFFICIENCY AT MCR CONDITION98.55%

SHORT CIRCUIT RATIO0.49

NEGATIVE SEQUENCE CURRENT CAP.I2T=8

DIRECTION OF ROTATION VIEWED FROM SLIP RING SIDECLOCKWISE

PHASE CONNECTIONDOUBLE STAR

NO. OF TERMINALS BROUGHT OUT9( 6 NEUTRALS AND 3 PHASES)

Rotor shaft made up of chromium nickel molybdenum and vanadium steel.

Rotor winding made up of silver bearing copper.

Rotor slot wedges made up of duralumin.

11.1 STATOR FRAME:

It is a totally enclosed gas tight fabricated structure made up of high quality mild steel and austenitic steel. It is suitably ribbed with annular rings called inner walls to ensure high rigidity and strength. Size of inner walls is selected on the basis of vibration considerations resulting partly in greater wall thickness than required from the point of view of mechanical strength. The natural frequency of stator body is well away from any of the exciting frequencies. Inner and sidewalls are suitably blanked to house four longitudinal hydrogen gas coolers inside the stator body.

11.2 PIPE CONNECTIONS:

To attain a good aesthetic look the water connection to the gas coolers is done by routing stainless steel pipes inside the stator body which emanate from the bottom and emerge out of the side walls. These pipes serve as inlet and outlet for the gas coolers. From sidewalls these are connected to gas coolers by means of 8 u tubes outside the stator body. For filling the generator with hydrogen, a perforated manifold is provided at the top inside the stator body. The feed and vent terminating flanges for hydrogen, carbon dioxide and air are provided at the bottom of the stator body.

11.3 TERMINAL BOX:

The beginnings and the ends of the stator winding are brought out to the slip ring side of the stator body and brought out through 9 terminal bushings in the terminal box.

11.4 STATOR CORE:

A rotating magnetic flux threads with the core. In order to minimize the magnetizing and eddy current losses in this active portion of the stator. The entire core is built up of thin laminations. For reasons of manufacture, each lamination layer is made up of a number of individual segments.

The segments are stamped out with accurately finished die from sheets of cold rolled high quality silicon steel. Before insulating with varnish each segment is carefully deburred. The stator body is turned on end while the core is stacked with lamination segments in individual layers as shown. The segments are assembled in an interleaved manner from layer to layer so that a monolithic core of high mechanical strength and uniform permeability to magnetic flux is obtained. The stampings are held in position by twenty core bars having dovetail section. Insulating paper pressboards are also put between the layer of stampings to provide additional insulation and to localize short circuit which may occur due to failure of varnish insulation of sheet stamping. To ensure tight monolithic core the stampings are hydraulically compressed during the stacking procedure at different stages when a certain heights of stack are reached forming different pockets. Between two packets one layer of ventilating segments is provided. The steel spacers are spot welded on stamping as shown.

These spacers form ventilating ducts from where the cold hydrogen from gas coolers enter the core radially inwards there-by taking away the heat generated due to eddy current losses.

The pressed core is held in pressed condition by means of two massive non-magnetic steel castings of Press Ring. The press rings are bolted to the ends of core bars. The pressure of pressing is transmitted to stator core stampings through press fingers of non-magnetic steel and duralium placed adjacent to press rings. The non magnetic steel press fingers extend up to the tip of stamping teeth so as to ensure the firm compression of the teeth part of the core portions too. The stepped arrangement of the stampings towards the bore at the two ends provides an efficient support of the tooth portion and contributes to a reduction of eddy current losses and local heating in this range in addition to the provision of more area of cross section for gas flow. To avoid heating of press rings due to end leakage flux two rings made of copper sheet are used as flux shield. The rings screen off the flux by short-circuiting. To monitor the formation of hot spots, resistance temperature detectors are placed along the bottom of slots.

11.5 GENERAL:

The stator has a three-phase double layer and bar type of windings having two parallel paths. Each slot accommodates two bars. The slot lower bars and slot upper bars are displaced from each other by one winding pitch and connected at their ends so as to form coil groups. The coil groups are connected together by bus bars inside the stator frame in conformity with the connection diagram.

11.6 CONDUCTOR CONSTRUCTION:

Each bar consists of solid as well as hollow conductors with cooling water passing through the latter. Alternate arrangements of hollow and solid conductors ensure an optimum solution for increasing current and to reduce losses.

The conductor of small rectangular cross-section are provided with glass lapped strand insulation. These are arranged side by side in two layers. The individual layers are insulated from each other by a separator. In the straight slot portion the strands are transposed by 360 degrees to reduce the eddy losses.

The transposition provides for a mutual neutralization of voltages induced in the individual strands due to the slot cross-field and end winding field and ensures that no circulating currents will arise.

The current flowing through the conductor is thus uniformly distributed over the entire bar cross section so that the current dependent losses are reduced.

At the roebal crossover points the insulation is reinforced by putting insulating strips of

thermosetting tape.

To ensure that strands are firmly bonded together and to give dimensional

stability in

slot portion, a layer of glass tape is wrapped over the complete stack. After that the stack

is pressed and cured in steam heated hydraulic press.

Prior to applying the bar insulation, overhangs on both ends of the bar is

formed as an involute in hydraulic press. Coil plugs for electrical and water connections

are brazed at both the ends.

Bar insulation is done with epoxy mica thermosetting insulation. This insulation is

void free and possesses better mechanical properties.

Thermosetting epoxy insulation is more reliable winding insulation, especially

for high voltages. The insulation is applied continuously to the slot and end turn

connections right up to the end connection. It thus provides effective protection against

over voltages arising in normal operation and against the high stresses that may occur

at the slot ends when high-test voltages are applied.

This insulation shows only a small increase in the dielectric dissipation factor with

increasing test voltage.

The bar insulation is cured in an electrically heated press and thus epoxy resin fills all the voids and eliminates air inclusion. The insulation is highly resistant to high temperature and temperature changes. The composition of insulation and synthetic resin permits the machine to be operated continuously under conditions corresponding to those of class B insulation.

11.7 ROTOR:

It is a long forging measuring about 9 metres in length and 1 metre in diameter. High quality heat-treated steel is used whose main constituents are chromium, molybdenum, nickel and vanadium. The shaft and body are forged integral to each other by drop forging process. On two thirds of its circumference the rotor body is provided with longitudinal slots to accommodate field winding. Slot pitch is selected in such a way that the displacement between two solid poles is 180 degrees. Additional slots of short length are provided on poles. One acts as an outlet for the hydrogen, which cools the over hang, and the other is used to accommodate damper segments acting as damper windings. Longitudinal slots are milled on sophisticated milling machines. These slots house the field winding. One north and one South Pole are obtained on the shaft. The conductors are made up of hard drawn silver bearing copper. It has low electrical resistance and high creep resistance so that the coil deformation due to thermal cycling at the start operation is minimized. Layer of glass laminates insulates the individual turns from each other. This laminate is built by glass prepeq strips on the turn of copper and baked under temperature and pressure. Coils are insulated from the rotor body by u-shaped glass laminate moulded slots troughs made of glass cloth impregnated with epoxy varnish. The rotor winding is cooled by means of direct cooling method or gap pick up method. Hydrogen in gap is sucked through elliptical holes on the rotor wedges and is directed to flow along lateral vent ducts on rotor. Winding is secured in slots by slot wedges made from duralumin alloy of copper, magnesium and aluminium. Slot wedges behave as damper winding bars during unbalanced operation. Slip rings consist of hexially grooved alloy steel rings shrunk on the rotor body shaft. Both rings are mounted on single bush. Slip rings are connected to the field winding through a semi flexible copper leads and current carrying bolts. Two semi circular copper bars insulated from each other and shaft are placed in a central bore of rotor joining two sets of current carrying bolts. The rotor shaft is supported on pedestal type of bearing. Rotor winding is solidly connected to the slip rings. Field current to the rotor winding is provided by a brush gear. Brush gear is rigidly fixed on the exciter side. Two brush gear stands each made of two symmetrical silicon brass casting half rings. The brushes are spring-loaded type to maintain required contact pressure of 0.2 kg/cm2. Brushes have low coefficient of friction and are self-lubricating provided with double flexible copper leads. Before filling brushes are rubbed with medium and fine sandpaper in the direction of rotation to obtain equal current distribution. Excessive pressure causes chattering and bouncing of brushes. Insufficient pressure tends to cause sparking. Hot hydrogen gas is cooled by four gas coolers mounted longitudinally inside the stator body. It consists of cooling tubes of brass with coiled copper wires wound on them to increase the cooling surface.

11.8 STARTING OF GENERATOR:

Before starting following work should be completed:

1. All constructional work.

2. Erection of auxiliary and main equipment.

3. Checking of oil, water and gas systems.

4. Checking and setting of all protection and signaling schemes.

5. Safety precautions including fire fighting.

Before starting following is to be ensured:

1. Proper supply of oil in the bearings.

2. Fill the generator with hydrogen upto the desired purity and rate pressure.

3. Charge the stator with distillate.

4. Generator circuit breaker should be open.

5. Field breaker should be open.

When the generator comes to the rated speed check the:

1. Temperature of bearing babbit seal and bearing drain oil.

2. Performance of brush gear.

3. Phase sequence of generator.

4. Bearing vibration in all directions.

After ensuring that the mechanical running of the set is normal, field breaker is switched on.

11.9 SYNCHRONIZATION:

CONDITIONS:

1. Phase sequence should be same.

2. Generator and system voltage should be in phase. Angle difference not to be more than 10 degrees.

3. Effective value of voltage should be same.

4. Frequency should be same.

Generator can be synchronized in auto as well as manual mode.

11.10 UNLOADING AND SHUT DOWN:

1. Reduce the load on unit by operating the turbine side controls.

2. Simultaneously, reduce the reactive load by de exciting the machine.

3. Open the generator line circuit breaker.

4. Cut out the auxiliary to manual mode

5. Seal oil supply should be kept ON as long as gas is under pressure.

6. Bearing oil supply should also be kept in operation.

7. Cooling water to gas cooler may be stopped. For prolonged shut down dry compressed air is blown into the winding at 850 m3/hr to drain out the distillate.

8. To achieve uniform cooling during shut down, the machine is put on barring speed for some time. Even after shut down the rotor is to be turned through 180 degrees periodically to avoid thermal deflection of rotor.

9. During shut down all excitation should be removed at the time speed reaches 2000 rpm. If not done temperature of the rotor will increase as ventilation decreases due to decrease in speed.

11.11 STATOR WATER COOLING SYSTEM:

One of the efficient ways of taking away the losses due to heat from the winding of any machine is by direct cooling using water. High quality demineralized water is circulated through the hollow conductor of the stator winding. The cooling water must have conductivity less than 2.5 micro mho/cm.

Cooling circuit make use of either of the following water supplies:

1. Distilled water.

2. Fully demineralized water from boiler feed water plant.

3. Condensate.

Water from the feed water plant or condensate may only be used if no chemicals such as ammonia, hydrazine or phosphates are present in water. A part of water is bypassed and is treated in mixed bed ion exchanger, connected in parallel with the stator winding, magnetic filter and expansion tank and returned to the section side of water pump.

The heat absorbed by the Demineralized water is dissipated to the secondary coolant in the primary water cooler.

Water treatment plant provided across stator winding, essentially comprises of an exchange tank filled with anions and cations resins. The base substance of the exchanger resins is generally a polymer containing group of diverse char