A REPORT OF THE VOCATIONAL TRAINING

MEJIA THERMAL POWER STATIONBy

Bappaditya MaityMCKV INSTITUTE OF ENGINEERING

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INTRODUCTION

Damodar Valley Corporation was established on 7th July 1948.It is the most reputed company in the eastern zone of India. DVC in established on the Damodar River. It also consists of the Durgapur Thermal Power Plant in Durgapur. The MTPS under the DVC is the second largest thermal plant in West Bengal. It has the capacity of 2340MW with 4 units of 210MW each, 2 units of 250MW each & 2 units of 500 MW each. With the introduction of another two units of 500MW that is in construction it will be the largest in West Bengal. Mejia Thermal Power Station also known as MTPS is located in the outskirts of Raniganj in Bankura District. It is one of the 5 Thermal Power Stations of Damodar Valley Corporation in the state of West Bengal.

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TECHNICAL SPECIFICATION OF MTPS:

INSTALLED CAPACITY: -1)Total number of Units : - 4 X 210 MW(unit 1 to 4) with Brush Type Generators, 2 X 250 MW(unit 5 and 6) with Brush less Type Generators, 2*500 MW(unit 7 and 8) Generators.2)Total Energy Generation: - 2340 MW3)Source of Water: - Damodar River4)Sources of Coal: - B.C.C.L and E.C.L, also imported from Indonesia

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OVERVIEW OF A THERMAL POWER PLANT

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STEAM TURBINEA steam turbine is a prime mover which continuously converts the energy of high pressure, high temperature steam supplied by the boiler into shaft work with low pressure, low temperature steam exhausted to a condenser

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BOILER SYSTEMBOILER:Working principle of Boiler (Steam Generator): In Boiler, steam is generated from de- mineralized water by the addition of heat.The heat added has two parts: sensible heat and latent heat. The sensible heat raises the temperature and pressure of water as well as steam. The latent heat converts water into steam (phase change). This conversion is also known as boiling of water, which is dependent on pressure and corresponding temperature.Thermodynamically, boiling is a process of heat addition to water at constant pressure & temperature.

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COAL HANDLING PLANTGenerally most of the thermal power plants uses low grades bituminous coal. The conveyer belt system transports the coal from the coal storage area to the coal mill. Now the FHP(Fuel Handling Plant) department is responsible for converting the coal converting it into fine granular dust by grinding process. The coal from the coal bunkers.Coal is the principal energy source because of its large deposits and availability. Coal can be recovered from different mining techniques like

• shallow seams by removing the over burnt expose the coal seam• underground mining.

The coal handling plant is used to store, transport and distribute coal which comes from the mine. The coal is delivered either through a conveyor belt system or by rail or road transport. The bulk storage of coal at the power station is important for the continues supply of fuel. Usually the stockpiles are divided into three main categories.

• live storage• emergency storage• long term compacted stockpile

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WATER TREATMENT PLANTRaw water supply:Raw water received at the thermal power plant is passed through Water Treatment Plant to separate suspended impurities and dissolved gases including organic substance and then through De-mineralised Plant to separate soluble impurities.Deaeration:In this process, the raw water is sprayed over cascade aerator in which water flows downwards over many steps in the form of thin waterfalls. Cascading increases surface area of water to facilitate easy separation of dissolved undesirable gases (like hydrogen sulphide, ammonia,volatile organic compound etc.) or to help in oxygenation of mainly ferrous ions in presence of atmospheri oxygen to ferric ions. These ferric ions promote to some extent in coagulation process.

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DM (Demineralised Water) PlantIn De-mineralised Plant, the filter water of Water Treatment Plant is passed through the pressure sand filter (PSF) to reduce turbidity and then throughactivated charcoal filter (ACF) to adsorb the residual chlorine and iron in filter water.

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Induced draft fan (ID fan):Induced draft represents the system where air or products of combustion aredriven out after combustion at boiler furnace by maintaining them at a progressively increasing sub atmospheric pressure. This is achieved with the help of induced draft fan and stack. Induced draft fan is forward curved centrifugal (radial) fan and sucks the fly-ash laden gas of temperature around 125°C out of the furnace to throw it into stack (chimney). The fan is connected with driving motor through hydro-coupling or with variable frequency drive (VFD) motor to keep desired fan speed.Forced draft fan (FD fan):

Forced draft represents flow of air or products of combustion at a pressure above atmosphere. The air for combustion is carried under forced draft conditions and the fan used for this purpose is called Forced Draft (FD) fan. It is axial type fan andis used to take air from atmosphere at ambient temperature to supply air for combustion, which takes entry to boiler through wind box. In all units except Durgapur TPS Unit #4, this fan also supplies hot /cold air to the coal mills. The output of fan is controlled by inlet vane / blade pitch control system.

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Cooling tower

Cooling towers cool the warm water discharged from the condenser and feed the cooled water back to the condenser. They thus reduce the cooling water demand in the power plants. Wet cooling towers could be mechanically draught or natural draught. In M.T.P.S the cooling towers are I.D. type for units 1-6 and natural draught for units 7&8.

CHIMNEY

•The chimney is 275 meters' high and 50,000 tonnes of reinforced concrete were used to make it

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ELECTRICAL OPERATIONThe electrical operation of a power plant comprises of generation, transmission and distribution of electrical energy. In a power station both distribution and transmission operation can take place. When power is sent from power station to all other power station in the grid, it is known as distribution of power. When power plant is driving power from other power station it is known as transmission of power/electrical energy.

ELECTRIC GENERATORIn M.T.P.S. there are 6 electric generators for units 1 to 6. These are 3 phase turbo generators, 2 pole cylindrical rotor type synchronous machines which are directly coupled to the steam turbine. The generator consist of 2 parts mainly the stator and the rotor. Rating of the turbo generator

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Rated kW capacity 210000 kW

Rated kVA capacity 247000 kVARated terminal voltage 15750 V

Rated power factor 0.85 lagRated stator current 9050 amps

Rated speed 3000 RPMRated frequency 50 Hz

Efficiency at rated power output & power factor

98.55%

Power factor short circuit ratio 0.49

TRANSFORMERSThe electricity thus produced by the generator then goes to the generating transformer where the voltage is increased for transmission of electricity with minimized copper losses.

Generating transformer#1 to 4MVA: 150/200/250 (H.V.) MVA: 150/200/250 (L.V.)Volts at no load: 240000 (H.V.) Volts at no load: 15750 (L.V.) Ampere line value: 361/482/602 (H.V.)Ampere line value: 5505/7340/9175 (L.V.) Phase-3 frequency: 50 Hz.Mass of core and windings: 139000 kg.Mass of oil: 38070 kg. Mass of heaviest package: 164000 kg. Connection: YNd1 connection.Generating transformer#5 and 6MVA: 189/252/315 (H.V.) MVA: 189/252/315 (L.V.)Volts at no load: 16.5kV (L.V.) Volts at no load: 240kV (H.V.) Ampere line value: 757.57 (H.V.)Ampere line value: 11022.14 (L.V.) Phase-3 frequency: 50 Hz.Mass of core and windings: 155000 kg.Mass of oil: 53070 kg. Mass of heaviest package: 18000 kg.

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The basic components of a switchyard are as follows:1.Circuit breaker: A circuit breaker is an equipment that breaks a circuit either manually or automatically under all conditions at no load, full load or short circuit. Oil circuit breakers, vacuum circuit breakers and SF6 circuit breakers are a few types of circuit breakers.2.Isolator: Isolators are switches which isolate the circuit at times and thus serve the purpose of protection during off load operation.3.Current Transformer: These transformers used serve

thepurpose of protection and metering. Generallythe same transformer can be used as a current or potential transformer depending on the type of connection with the main circuit that is series or parallel respectively.In electrical system it is necessary toa)Read current and power factorb)Meter power consumption.c)Detect abnormalities and feed impulse

to protectivedevices.

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5.POWER TRANSFORMER:The use of power transformer in a switchyard is to change the voltage level. At the sending and usually step up transformers are used to evacuate power at transmission voltage level. On the other hand at the receiving end step down transformers are installed to match the voltageto sub transmission or distribution level. In many switchyards autotransformers are used widely for interconnecting two switchyards with different voltage level (such as 132 and 220 KV)

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CONCLUSIONThe practical experience that I have gathered during the overview training of large thermal power plant having a large capacity of 2340 MW for Unit# I to VIII in three weeks will be very useful as a stepping stone in building bright professional career in future life. It gave me large spectrum to utilize the theoretical knowledge and to put it into practice. The trouble shooting activities in operation and decision making in case of crisis made me more confident to work in the industrial atmosphere.Moreover, this overview training has also given a self realization & hands-on experience in developing the personality, interpersonal relationship with the professional executives, staffs and to develop the leadership ability in industry dealing with workers of all categories.I would like to thank everybody who has been a part of this project, withoutwhom this project would never be completed with such ease.

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