Thermal Training

TRAININGREPORT Guru Nanak Dev Thermal Power Plant Bathinda Submitted by: Yogesh Kumar-UE99078 BE Mechanical ACKNOWLEDGEMENT Myself YOGESH KUMAR a 3rd year student of UIET,PU CHD. express my deepest gratitude to all who contributed in imparting me the valuable knowledge during my training. I am thankful to the Chief Engineer/Administration, GNDTP who provided me the opportunity to undergo training . With the help and valuable time of all the people I would not have been able to learn and gather various important aspects of the MECHANICAL works during my training. Finally,yet importantly,I would like to express my heartfelt thanks to my beloved parents for their blessings,my friends/classmates for their help and wishes for the successful completion of my training. INDEX 1. ORAGAZNISATION : AN INTRODUCTION 2. FUNCTIONAL DESCRIPTION 3. 6.6 KV CIRCUIT BREAKERS 4. MOTOR a. H.T.MOTORS b. L.T MOTORS 5. TRANSFORMERS 6. SWITCH YARD COMPONENTS 7. TURBO GENERATOR ORANISATION:-AN INTRODUCTION Thermal power stations require a number equipments performing a number of complex processes with the ultimate aim to convert chemical energy of coal or oil to electrical energy. This involves the generation of steam in boiler by burning coal and /or oil. The steam in turn drives the turbine. The generator coupled with the turbine produces electricity 11 kv which is stepped u 220kv with the help of transformers and is fed into grid station through transmission lines. INTRODUCTION Cheap and abundant supply of electric power is the major factor in the development and progress of country.Punjab power sector comprises three wholly state-owned corporations vizThe Guru Nanak Dev Thermal Plant ,Guru Hargobind Thermal Plant and Guru Gobing Singh Super Thermal Power Plant which are responsible for power generation,transmission,distribution and trading in the state. LOCATION: The Guru Nanak Dev Thermal Plant ( ਥਮਲ ਲ )at Bathinda is one of the three thermal power stations in Punjab (the other being at Lehra Mohabat and Ropar) .It is a medium-sized power station with four units that were begun to be built in early 1970s and completed in 1982. All total generate up to 440 Mw of power that meets the mammoth irrigation needs of lower Punjab. At couple of years back the Thermal Plant's functioning, which some claim is not up to contemporary environment safety standards, has given birth to serious health problems, not only in Bathinda itself, but also nearby towns and villages, especially fly ash problem. Input &outputs There are three major inputs or raw materials required for the type of thermal power station these are: 1. WATER 2. FUEL OIL 3. COAL 1. WATER:- The raw water required for the thermal power station has been taken from BATHINDA CANALS through a channel. This water is lifted by RAW WATER PUMPS and fed into clarifiers to remove the turbidity of the water.The clean water is stored in CLEAR WELLS from there it is sent to WATER TREATMENT PLANTS,COOLING WATER SYSTEM AND SERVICE WATER SYSTEMS. The water in the WATER TREATMENT PLANT Is FILTERED and DEMINERALISED WATER (D.M water) is stored in bulk storage tanks for use in boiler and turbine .The cool water for condensation of steam is circulated with the help of condensate water (C.W) PUMPS through COOLING TOWERS. The hot water from the outlet of the condenser is sprayed in the cooling tower to reduce its temperature. Some part of it is used in cooling various auxiliaries in plant through BEARING COOLING WATER PUMPS. 2. FUEL OIL:- In this power house three type of fuel oil are used for preheating and at low load of the boiler due to less problem faced in ignition of oil rather than coal. These three types are: 1. High speed diesel oil. 2. Heavy furnace oil. 3. Low sulpher heavy stock. The high speed diesel oil reaches power station by LORRY TANKERS. The oil is decanted through pumps and team heating H.F.O& L.S.H.S is stored in BULK STORAGE TANKS. The H.F.O&L.S.H.S comes to site through rail tankers. As this oil is viscous, it is heated with steam and decanted with pumps. The oil is stored in bulk storage tanks with steam heating coil .H.F.O & L.S.H.S is burnt in the furnace of boiler after atomizing with steam. 3. Coal The coal reaches the power station in RAILWAY WAGONS.The daily consumption of coal in stage-I is about 1500 M tonnes.The unloading of the coal from railways wagons is done mechanically by tilting the wagon by WAGGON TIPPLER. The coal is then sent to COAL CRUSHER by conveyor belts. The crushed coal is then sent either to coal mill bunkers or storage yard. The coal is also transported to coal bunkers from storage yard. The coal is also transported to coal bunkers from storage yard through conveyor belt when the coal wagons are not available. The crushed coal stock from the mill bunker goes to coal mills through RAW COAL FEEDERS where it is further pulverized to power form & is then transported to the furnace of the boiler with the help of PRESSURED AIR from PRIMARY AIR (P.A.) FANS. FUNCTIONAL DESCRIPTION The thermal power station burns fuel & uses the resultant to make the steam, which derives the turbo generator. The fuel i.e. Coal is burnt in pulverized form. The pressure energy of the steam produce is converted into mechanical energy with the help of turbine. The mechanical energy is fed to the generator where the magnets rotate inside a set of stator winding & thus electricity is produced. In India 65% of total power is generated by thermal power stations. To understand the working of the thermal power station plant, we can divide the whole process into following parts:  COAL FLOW: In coal fired plants, raw materials are air &water. In GNDTP, coal is transported through railway wagons from m\s. coal India & is kept reserved on a buffer stock. The brought out to the station is unloaded with the help of wagon tippler. After unloading, the coal is sent to crusher house with the help of conveyor belts. The coal which is now reduced to very small pieces is sent to the coal bunkers with the help of conveyor belt .The raw coal is fed to coal mills through raw coal feeders. Raw coal feeders basically regulate raw coal to pulverize mill. The raw coal is fed to the furnace with the help of primary fan through pulverized coal pipes. A portion of the primary air is Heated utilizing the heat of the flue gases & then mixed with the cold air as per requirement by the pulverized coal. Normally the temp. is maintained at 60 to 70 degrees. The coal is now burnt in the furnace using oil in the beginning, showered through the nozzles at different elevations in the furnace. To provide air for combustion, the heat of the flue gases also heat, if the heat produced due to combustion is utilized for the conversion of water into steam. This water is stored in the boiler drum. There are two sets of pipes attached to the drum, one called riser & other known as down corner through which the water comes to the ring header & steam moves up due to the density difference of water & steam. This steam is super heated using super heaters & meanwhile the flue gases are through out in the atmosphere through chimney. 2. STEAM FLOW: The super heated steam is sent to the turbine through pipelines. There are three turbines in the units, using this steam at different temp & pressures. After passing through high pressure turbine the steam is send to the reheater for raising the temp. Of the steam after reheating the steam is sent to the intermediate pressure turbine through reheated line. Here it losses most of its temp. & pressure, & finally sent to low pressure turbine. The use of three different turbines helps in increasing the efficiency of the Plant. The turbine in turn connecting with a generator produces electricity. Then this electricity is step up to 220 Kv with the help of step up transformer & supplied to various substations/grids. Meanwhile, the steam through low pressure (L.P.) turbine is condensed and the condensed water is stored in hot well. 3. WATER FLOW: The condensed water is extracted from the hot well through condensate extraction pumps & sent to the boiler drum with the help of boiler feed pump (B.F.P.) before passing through low pressure heater and deaerator. While loss in water is make up from C.S. tank, which have D.M. door in it. The C.S tank is directly connected to hot well. The water used in condenser is sent to cooling tower for cooling. After cooling this water is again sent to condenser with the help of Acirculating water pump. The loss is making from raw water pump house through clarifier pump house. EXPLANATION OF LAYOUT DIAGRAM 1 WAGON TIPPLER:- The coal may be transported to the plant site by rail wagons. The coal is unloaded at the plant site mechanically by means of wagon tipplers. The loaded wagon is emptied by tippling it in the underground coal hopper from where the coal is carried by belt conveyer to the crusher house. 2.CRUSHER: Coal unloaded by wagon tippler is carried to crusher house conveyors for crushing. Here the coal is crushed to a size of 20mm.the crushed coal is then supplied to boiler raw coal bunkers. The surpluse coal is carried to coal storage area by means of belt conveyors. Crushing of coal is essential for its optimum pulverizing and safe storage. 3 COAL MILLS: In it small pieces of coal are converted into pulverized form. They are 6 in number. 4. FURNACE:- It is the chamber in which fuel burns & fire blows. In addition it provides support and enclosures for the combustion equipments i.e burners. 5.BOILER DRUM:- A steam generator or a boiler is a combination of systems and equipment in which the chemical energy of fossil fuels is converted into thermal energy which is then transferred to a working fluid so as to convert it into steam at high pressure and temperature. This high pressure and temperature steam is then used for the development of power in a turbine. 6.ELECTROSTATIC PRECIPITATOR:- In this we have electrodes which attracts fly ash and extract it from flue gases so that it can not enter atmosphere. 7 CHIMNEY:- The flue gases from the boiler after removal of the fly ash in the precipitators,are let off to atmosphere through boiler chimney. 8. TURBINE:-Turbine is the part which revolves due to steam pressure. It is of three types: a).HIGH PRESSURE TURBINE b).INTERMEDIATE PRESSURE TURBINE. c).LOW PRESSURE TURBINE. 9. TURBOGENERATOR:-It is the main machine which produces 110 mw electricity. It is H2(hydrogen) gas cooled. Therefore it is contained in cylindrical chamber. 10.CONDENSER:- It condense steam coming from low pressure turbine(L.P.T.) to hot water. By removing air and other non-condensable gases from steam while passing through them. 11.COOLING WATER (C.W.) PUMP :- This pump send water from cooling tower to condenser. 12.COOLING TOWER:- It is used to cool the water its height is near about 143.5 mtr. The hot water is led to the tower top and falls down through the tower and is broken into small particles while passing over the baffling devices. Air enters the tower from the bottom and flow upwards. The air vapourises a small percentage of water, thereby cooling water falls down into tank below the tower from where it is pumped to the condenser and cycle is repeated. 13.RAW WATER PUMP HOUSE :- It supplies raw water to the boiler. 14.CLEARIFIER PUMP HOUSE:-The water from raw is clear at clarifier by putting alum in it & filtering it & then supplied to the condenser. 15.CONDENSATE EXTRACTION PUMP:- C.E.P.Pump is used to extract the condense water from the hot well and supply to the deaerator after passing through L.P. Heater& economiser, so that high pressure steam in the cylinder can be created. 16.LOW PRESSURE HEATER:- It is used to increase the temperature of water, in this way efficiency of system increases. 17.DEAREATER:- It is used to remove air from water, which is entrapped in the water molecules. It very important part because the entrapped air effect air drum badly. 18.BOILER FEED PUMP(B.F.P.):- It is the heaviest drive in the plant & supply water to boiler drum from deaerator. 19.HIGH PRESSURE HEATER(H.P.):- In this temperature of water increases, thus efficiency further increases. 20. ECONOMISER:- In this flue gases exchange heat to the water to increase system efficiency, causes saving in fuel consumption(5 to 10%). Economiser tubes are made up of steel either smooth or covered with fins to increase the heat transfer surface area. 6.6 KV CIRCUIT BREAKER A circuit breaker is a device which:- 1 Makes or breaks a circuit either manually or by remote control under normal conditions. 2 Breaks a circuit automatically under fault conditions. Thus a circuit breaker is just a switch which can be operated under normal & abnormal conditions both automatic or manually. To perform this operation, a circuit breaker is essential consisting of fixed and moving contacts called electrodes. When a fault occurs on power system, the trip coil of circuit breakers energized which pulls apart moving contacts, thus open the circuit dc supply is used for the operation of circuit breaker. On the basis of medium used for extinction the circuit breaker are classified as: 1 OIL CIRCUIT BREAKERS 2 AIR BLAST CIRCUIT BREAKER 3 SULPHER HEXAFLURID CIRCUIT BREAKER. Oil circuit breaker It is well known that when a circuit carrying a large current is broken, an arc occurs at that point where the contacts are separate; the arching is specially severe when high voltages are involved and if a short circuit occurs on a high voltage cable which is supplied from large power station. The arc would be powerful to bridge the contacts of the switch and destroy it by burning. The device is employed as an oil breaker. An oil breaker posses the property of always breaking an alternative current at its zero value. These switches are suitable for a maximum voltage of 6.6 kv. The contacts of these switches, which break high tension circuit, are immersed in oil to ensure rapid & effective rapture of the circuit. When the arc occurs, the oil in its path is vaporized and the gas thereby generated extract a pressure on the surrounding oil. This pressure is utilized in arc controlled devices to cause a movement of fresh cool oil across the path of the arc, thereby efficiently assisting its interruption. Pictorial diagram: AIR BLAST CIRCUIT BREAKER All air blast circuit breaker requires an auxiliary compressed air system which supplies air to the breaker air receiver. When opening is required, compressed air is admitted to the arc extinction chamber. It pushes away the moving contacts. In doing so the contacts are separated and the air blast takes away the ionized gases along with it and assists arc extinction. Air blast circuit breaker extinguishes the arc. Within one or two cycle and arc chamber is filled with a high pressure air, which prevents restrike. SULPHER HEXAFLURID CIRCUIT BREAKER In SF6 Circuit breaker SF6 gas is blown axially along the arc. The heat is removed from the arc by axial convection and radial dissipation. Consequently, the arc diameter reduces during the decreasing node of the current wave. The diameter becomes small during current zero. Turbulent flow is introduced around current zero for extinguish the arc. The above diagram show the layout diag of SF6 circuit breaker. . MOTORS:- HIGH TENSION MOTOR : 1 CIRCULATING WATER(C.W.P.) PUMP MOTORS:- FUNCTION:- C.W. pump is used to circulate cooling water to the condensers so that low pressure steam in the cylinder can be converted into water. 2 CONDENSATE EXTRATION PUMP(C.E.P.) PUMP MOTOR:- FUNCTION:-C.E.P. pump is used to extract the condense water from the hot ll and supply to the deaerator after passing through L.P. Heater& economiser, so that high pressure steam in the cylinder can be created. 3.BOILER FEED PUMP(B.F.P.) MOTOR:- FUNCTION:-Its function is to supply the water to the boiler drum. It takes water from the deaerator by creating strong suction. It is the biggest motor in the plant. 4.COAL MILL MOTOR:- FUNCTIONS:- Its function is to grind the coal pieces to fine powder (pulverized) form i.e. upto size of 25 micron. 5 PRIMARY AIR FAN MOTOR:- FUNCTION:- Its function is to carry pulverized coal from the coal mill to the furnace for its ignition. It creates strong draft of air that carries pulverized coal. 7). FORCE DRAUGHT (F.D.) FAN MOTOR:- FUNCTION:-F.D. fan is used to supply fresh air to the furnace for the proper ignition of coal into the furnace. 8). INDUCED DRAFT (I.D.) FAN:- FUNCTION:-Its function is to discharge flue gases to the atmosphere through the chimney after passing through the precipitation. LOW TENSION MOTOR 1. B.C.W. DRAIN MOTOR:- FUNCTION:-IT PUMP THE B.C. WATER TO THE PUMP. 2. SEAL WATER PUMP MOTOR:- FUNCTION – It provides a layer of water to the lower position of boiler in order to seal it from the entry of atmospheric air. 3.SEAL WATER VAPOUR EXHAUST FAN :- FUNCTION- It prevents the entry of air bubbles in the turbine cylinder by providing the opposite push. 4. CENTIFUGE PUMP MOTOR – FUNCTION – To centrifuge the vapour that enters by change in turbine an remove them. 5 ASH SULRRY PUMP MOTOR: – FUNCTION – To pump ash slurry to the ash disposal area. 6. EMERGENCY OIL PUMP(A.C): – FUNCTION – To provide oil to the shaft and bearing of the turbine if seal oil pump and taking oil pump fails. 7. RAW WATER MOTOR PUMP: FUNCTION- It is use to pump raw water from the lake to the plant. 8. INSTRUMENT AIR COMPRESSOR:- FUNCTION- It is used to compress the air used to control pneumatic controlled instruments at pressure 6 to 7 kg/cm cube. 9. SERVICE AIR COMPRESSOR:- FUNCTION- Its function is similar to instrument air compressor. 10.CLARIFIER WATER PUMP MOTOR- FUNCTION- It pump the filtered water from clarifier to D.M. water treatment plant. TRANSFORMERS The transformer is the most convenient & economical device for transfer of power from one voltage to another voltage at the same frequency. It works on the principle of electromagnetic induction. There is hardly any installation without a transformer. Due to this equipment, it has been possible to transmit bulk power to load centers from far off power houses and to various machineries and switchgears of the power plant. Transformers are of two types:- #STEP-UP TRANSFORMER - which step-up the voltage at secondary side called step-up transformer. #STEP-DOWN TRNSFORMER- which step-down the voltage at secondary side are called step-down transformer. MAIN PARTS OF POWER TRANSFORMERS # PRIMARY WINDING # SECONDRY WINDING # OIL TANK # DRAIN COKE # CONSERVATOR # BRETHER # TUBES FOR COOLING # TRNSFORMER OIL # EARTH POINT # EXPLOSION VENTS # TEMPERATURE GAUGE # BUCHHOLZ RELAY # PRIMARY TERMINALS # SECONDARY TERMINALS SOME ACCESSORIES OF TRANSFORMERS ARE DESCRIBED BELOW:- 1.OIL CONSERVATOR:- Oil conservator is a short of drum mounted on the top of transformer. A level indicator is fixed to it, which gives alarm at low level. Conservator is connected through a pipe to the transformer tank containing oil. This oil expands & contract depending upon the heat produced & so the oil level in conservator is left open to the atmosphere through a breather so that the extra air may go out or come in. 2. BREATHER: The breather is a box containing calcium chloride or silica gel to absorb moisture of our entering the conservator as it is well known fact that the insulating property of the transformers oil is lost if a small amount of moisture enter in it. So dry air is allowed to pass through the breather. When oil level in oil conservator changes, air moves in & out of the conservator. This action is known as breathing. Dry silica gel is of the blue color. It turns pale pink as it absorbs moisture. The wet silica gel can be regenerated by drying. 3.BUCHHOLZ RELAY:- This relay is a gas-actuated relay which is meant for the protecting of oil immersed transformer from insulation failure, core heating or any type of internal fault which may cause the heating of oil beyond the specified temp.. Due to any internal fault, oil is heated –up & oil vapours so formed causes either the alarm circuit(for less fault) or trip the circuit(for sever fault). 4.EXPLOSION VENT:- It is also a safety device of the transformer which protects the transformer tank from gases induced by & any type of short circuit in the transformer. This consists of a vertical pipe closed by a diapharm made of thin bakelite sheet. This diapharm burst or slides out in case of abnormal pressure inside the tank. A diverter plate is used at the bottom of the explosion vent to ensure that gases produce inside the transformer are directed toward the buchholz relay & don’t get collected inside the ventilation and equalize the pressure on each side of the diverter plate. 5. TEMP. INDICATOR:- It is also a protective device fitted to the transformer to indicate temp.of transformer oil. For measuring temp. Of the oil, bulb of the vapour pressure type thermometer is placed in the hot oil & dial of the thermometer is mounted outside the tank. Two indicating pointers black and red are provided. Alarm contacts are also provided which come into action when predetermined permissible higher temperature is reached under abnormal operating conditions. 6. BUSHING: – The bushing serves as supports and insulation of the bus bars and transformer terminal. The bushing consists of porcelain shell body, upper and lower locating washer used for fixing the position of bush bar and mounting flange with the hole drilled for fixing bolt and it is supplied with an earthing bolt. 7.MAGANETIC OIL GAUGE:- The magnetic oil level gauge supervises the level of oil in the conservator tank. The oil level gauge is provided on the transformer are of dial type with minimum and maximum level marking and a pointer which indicate the level of oil in the conservator. Sometime the scale is also graduated for oil temperature on the basis of its level. 8.TAP CHANGER:– The voltage control of transmission And a distribution system is obtained by tap changer. Tap changer are either on load or off load tap changer. Tap changer is fitted with the transformer for adjusting secondary voltage. IMPORTANT TRANSFORMERS IN THE PLANT 1. GENERATOR TRANSFORMER ( 11KV/220 KV)– It converts 11 kv to 220 kv which is supplied from generator to 220kv and supplied it to the bus bar/ grid. 2.STATION SERVICE TRANSFORMER (40MVA, 220KV/7KV) – It converts 220kv which is coming to station from BBMB to 7kv and fed to station auxiliary. 3. UNIT AUXILIARY TRANSFORMER ( 11KV/6.6KV) – It converts 11kv which is supplied from generator and step down to 6.6kv to fed unit auxiliary. The unit auxiliary transformers are of two in no. The above three transformers are main transformers use in the plant. And special care is taken for the safety of the transformer. Time to time various tests is done for the safety of transformer. SWITCHYARD COMPONENTS 1.SWITCH-GEAR- Switch gear is a control switch that Control the operation of a power circuit. The two function of a switch in power systems are – I). To permit the transmission lines to be convenient put into and taken out from service. Ii). To disable the some plant and lines when these become faulty, to be rapidly and safely isolated by automatic means. The first of these can be served by relatively simple switches the second however require circuit breakers, which are more robust & capable of breaking the large value of fault power that results in faults on major power system. Since all plants and lines are liable to develop faults as results of mechanical damage, electrical breakdown, errors in operation etc. The simple isolators switch in favour of automatic circuit breakers even for switching function. The whole switchgear assembly consists of two parts:- 1. PANEL- Panel consists of protective relays, mounting of potential transformer, current transformer, ammeter, voltmeter & energy meter. The potential transformer is mounted on the panel. The primary is connected to 11kv & the reduce voltage from the secondary is given to energy meter as line voltages & for protective purposes. 2.TROLLY- The trolley consists of current carrying contacts called electrodes. These are normally engaged but in predetermined conditions, separate to interrupt the circuit, when the contacts are made. BUS BAR ARRANGEMENT Conductors to which a number of circuits are connected called bus – bars. In power plants, shut down results disconnection of supply to a large area. Hence to avoid shut down the major plants should have elaborate bus bar arrangement with duplicate buses, alternative supply arrangement section etc. the extra high voltage equipments such as isolators, circuit breaker are generally costly hence unnecessary equipment should not be provided.  SINGLE BUS BAR ARRANGEMENT:- The single arrangement consists of a single (three phase) bus bar to which various feeders are connected. In case of fault or maintenance of bus, the entire bus bar has to be de-energized and the total shutdown results. This scheme is most economical and simple.  DOUBLE BUS BAR ARRANGEMENT:- The double bus systems provide additional flexibility, continuity of supply and permit periodic maintenance. In the event of fault on the bus bar the other can be used the figure shows to the bus bar arrangement. There are two buses called main bus and reserve bus. The coupler can be closed so as to connect two buses while transferring the power to the reserve bus.  Closed bus coupler, the two buses are now at same potential.  Closed isolator on reserve bus.  Open isolator on main bus. LIGHTING ARRESTER A lighting arrester is device, which proves low impedance path for the flow of current between the line and earth when the systems voltage increases more than the desire value and regains its original properties of an insulator at normal voltage. It is connected between line and earth at the switch yard near the transformer. The lighting arresters are extensively used for protection of transformers, switch gears and electrical equipments of over head lines, power houses and sub-station . These are also use to protect the line and equipments from sky lighting. TURBO GENERATOR GENERAL:- Modern features of direct cooling by water & hydrogen are incorporated in the turbo generator, thus evolve an economical & reliable design. The machine is provided with a fast acting excitation system & dependable auxiliary service to give prolonged trouble free operation over the years. All the material that goes into the manufacture of this machine subjected to various test as per national & international standards. Each component undergoes series of stage wise tests. Description of various parts is given below:- 1. STATOR WINDING AND INSULATION:- The stator has a three phase, double layer, short chorded, bar type winding, having two parallel pats . Each coil side consists of glass insulated solid and hollow conductors with cooling water passing through the patter. The elementary conductors are rebel transposed in the slot portion of winding to minimize eddy current losses. Adequate protection is provided to avoid corona & other discharges. In the slots, the sides are firmly held in the position by fibrous slot wages, which are mechanically strong and have high dielectric properties. The overhang portion of the coil is securely lashed with glass chord to bondage rings& special buckets of non magnetic steel, which are in turn, fixed to the core press rings. On short circuits the forces between the conductor tend to open the cone formed by overhang portion of the coils, but the movement is effectively presented by supports & lashings. 2. DISTILLATE HEADERS OR STATOR WATER HEADER: - ring type water heads, made of copper are provided separately for distillate inlet & outlet in the stator on turbine side. The headers are supported on insulators and isolated from stator body. The winding ends are solidly soldered into the coil lugs which are than ultrasonically tested. Individual bars are provided with water inlet/outlet connections made of P.T.F.E. houses. The bar heads are insulated by fiber molded corners. The winding scheme along with the water connections. The complete water path assembly is subjected to the rigid hydrolytic pneumatic tests at various stages to ensure water tightness and to detect blocking of the flows paths. 3. TERMINAL BUSHINGS:- Water cooled terminal bushings are housed in the lower part of the stator on the slip ring side. Porcelain insulators are provided to insulate the terminal bars from the stator body. Effective sealing is provided between the terminal bushing and the stator body to avoid any possibility of leakage of hydrogen. Terminal bushing is housed inside a chamber made of non magnetic steel plates. Three phase terminals are brought out to facilitate external connections. The terminal plate of the end terminals, where bus bar connections are made is silver plated. The terminal bushings can be replaced without removing the stator from foundation. Provision is made for fixing the external bus ducts with the terminal plate. 4. ROTOR: - The rotor is of cylindrical type shaft and body being forged in one piece from chromium, nickel, molybdenum & vanadium steel. Prior to matching, a series of comprehensive ultrasonic examination and other tests are carried out on rotor body and shaft portion to ensure of any internal defects. The rotor with all the details assembled, dynamically balanced to a high degree of accuracy and subjected to 20% over speeding for 2 minutes ensuring mechanical strength. 5. FIELD WINDING:- The field winding is made from hard drawn silver bearing copper. Rotor winding is held in position against centrifugal forces by duralium forces wedges in the slot portion & by non magnetic steel retaining rings in the over hang portion. Gap pick up system is employed for direct hydrogen cooling of rotor winding. Several groups of ventilation ducts are mulled on the sides of the rotor coil for gas passage. The rotor slot wedges are of special profiles with elliptical holes rolled in to match the ventilation ducts on the winding stacks. The end windings are insulated from rings with the help of glass epoxy molded segments. Copper segmental type damper winding is provided in the end zone of rotor to prevent over heating of returning ring s during asymmetrical & asynchronous operation. 6. SHAFT MOUNTED FANS:- For circulating the cooling gas inside the generator, two propeller type fans are shaft mounted on this & of rotor body. Fan hubs are made from alloy steel forging and are hot fitted on the rotor shaft with sufficient interference. The alloy steel cast fan blades are machined in the tail portion to suit the fan hub and held in position with the help of conical pins. The blades can be easily removed from or assembled in the fan hub. Fan shields fixed to the end shields, guide the flow of gas through the fan sections. 7. SLIP RINGS:- The slip ring consists of helically grooved alloy steel rings shrunk on the rotor shaft & insulated from it. For convenience in assembly both the rings are mounted on a single, common steel bush, which has an insulated jacket pre molded on it. The complete bush with slip ring is shrunk on the rotor shafts. The slip rings are provided with inclined holes for self-ventilation. The helical groove cut on the outer surface of the slip rings improves brush performance