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Generating StationsSteam Power Station.Hydro-Electric Power Station.Diesel Power Station.Gas Turbine Power Plant.

IntroductionNecessity to provide bulk electric power economically.Bulk electric power can be achieved by the help of suitable power producing units called Power Plants / Electric Power Generating Stations.The design of power plant should in corporate two important aspects.Selection and placing of necessary power generating equipment, such that a maximum of return will result from a minimum of expenditure over the working life of the plant.The operation of the plant should provide cheep, reliable and continuous services.Generating StationA generating station essentially employs a prime mover coupled to an alternator for producing of electric power.The prime mover (Steam turbine, water turbine and etc) converts some form of energy to mechanical energy.Then alternator converts mechanical energy to electrical energy.The electrical energy produced by generating station is transmitted and distributed with the help of transmission line to various consumers. Auxiliary equipment and instruments are also employed to ensure cheap, reliable and continuous service.Generating Station (Cont.)Depending upon the various types of energy converted in to electrical energy, the generating station are classified as under.Steam Power Stations / Thermal Power Station.Hydro Electric Power Stations.Diesel Power Stations.Nuclear Power Stations.

Steam Power StationA generating station which converts heat energy of coal combustion in to electrical energy is known as Steam Power Station.Steam is produced in the boiler by utilizing the heat of coal combustion.Steam is expanded in the prime mover (Steam turbine) and is condensed in a condenser to be fed in to the boiler again.The steam turbine derives the alternator, which converts mechanical energy of turbine in to electrical energy.The type of power plant suitable where coal and water are available in abundance.

Steam Power Station (Cont.)AdvantagesThe fuel (i.e. coal) used is quiet cheep.Less initial cost as compared to other generating stations.It can be installed at any place irrespective of the existence of coal*.It requires less space as compared to the hydro-electric power stations.Cost of power generation is lesser than that of diesel power station.

DisadvantagesIt pollutes the atmosphere due to production of large amount of smoke and fumes.Its running cost is very high as compared to hydro-electric power station.* It can be transported by rail or road.6

Schematic Diagram of Steam Power Station Steam Power Station (Cont.)Choice of Site for Steam Power Station:In order to achieve overall economy, the following points should be considered while selecting a site for a steam power station.Supply of fuelAvailability of water Transportation facilityCost and type of landNearness of load centerDistance from populatedIt is clear that all the above factors can not be favorable at one place . However keeping in view the fact that nowadays the supply system is AC the more importance is given to the generation and transmission system. A site away from the site may be selected. In particular site by river side where sufficient water is available, No pollution of atmosphere occurs and fuel can be transported economically. May perhaps be an ideal site.8Steam Power Station (Cont.)*Heat lost in the condenser can not be avoided. It is because heat energy can not be converted in to the mechanical energy with out temperature difference. Greater the temperature difference greater the heat energy converted in to the mechanical energy.* This is the necessity to keep the steam in the condenser at low temperature. But we know that greater the temperature difference greater will be the amount of heat lost. This explains for the low efficiency of steam plant.9Steam Power Station (Cont.)*Means that if 100 calories is supplied by the coal combustion, then mechanical energy equivalent to 30 calories is available at turbine shaft and rest is losses.10Problem 2.1: A steam power generating station has an overall efficiency of 20% and 0.6 kg of coal is burnt per kWh of electrical energy generated. Calculate calorific value of fuel.11Problem 2.2: A thermal power station has the following data:Max. demand = 20,000 kW; Load factor = 40%;Boiler Efficiency = 85%; Turbine Efficiency = 90%; Cost of 1 ton of coal = Rs 300; coal consumption = 0.9 kg/kWh; Determine (i) thermal efficiency. (ii) Coal bill per annum

12Hydro Electric Power StationA generating station which utilizes the potential energy of water at a high level for the generation of electrical energy.In hydro electric power station, the turbine converts hydraulic energy (product of head and flow of water) in to the mechanical energy.Turbine drives the alternator which converts mechanical energy to electrical energy.

Hydro electric power stations are usually located in hilly areas where dam can be built conveniently and large water reservoir can be obtained 13Hydro Electric Power Station(Cont.)AdvantagesIt requires no fuel, as water is used for the generation of electrical energy.No hazardous effects*.Simple in construction and requires less maintenance. It does not require long starting time like steam power station.It is robust and has longer life.Such plants can be put in to service instantlyLow man powerDisadvantagesIt require high capital cost due to construction of dam.There is uncertainty about the availability of huge amount of water.High cost of transmission lines as plant is located at the hilly areas which are quiet away from the consumers.Skilled and experienced manpower required.* No smoke or ash is produced which is hazardous to health.

14Schematic Arrangement of Hydro-Electric Power Station

Hydraulic Structure:DamSpillwaysHeadworksSurge TanksPenstocksWater Turbines:Impulse TurbinesReaction TurbinesElectrical Equipment:15161718

Problem 2.12: The weekly discharge of hydroelectric plant is as under.

The plant has an effective head of 15m and an overall efficiency of 85%. If the plant operates on 40% load factor, estimate (i) average daily discharge. (ii)Pondage required. (iii) Installed Capacity of proposed plant.1920Diesel Power StationA generating station in which diesel engine is used as a prime mover for generation of electrical energy.The diesel burns inside the engine and the product of this combustion act as the working fluid to produced the mechanical energy.The diesel engine drives the alternator which converts electrical energy to mechanical energy.The generation cost is high due to the high price of diesel.Diesel power station is feasible where demand of power is low and sufficient amount of coal and water is not available and transportation facilities are inadequate Steam power station and hydroelectric power station are invariable used to generate bulk power at cheaper cost .It is only used for the stand by purposes to supply power to the important points like hospitals, radio stations and telephone exchange.21Diesel Power StationAdvantagesThe design and layout of plant are very simple.It occupies less space*.It can be installed at any place.It can be started quickly and can pick up the load in a very short time.There are no standby losses.Thermal efficiency is higher than other power plants.It requires less operating staff.DisadvantagesThe plant has high running charges as the fuel is costly.The plant does not operate satisfactorily under overload condition for a longer period. The plant can only generate small power.The cost of lubrication is generally high.The maintenance charges are generally high.*The number and size of auxiliaries is small.

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Schematic diagram of Diesel Power PlantSchematic diagram of Diesel Power PlantFuel Supply System:Air Intake System:Exhaust System:Cooling System:Lubricating System:Engine Starting System:Problem 2.14: A diesel power station has fuel consumption of 0.28 kg/kWh, the calorific value of fuel being 10,000 kcal/kg. Determined (i) The overall efficiency and (ii) Efficiency of the engine if alternator efficiency is 95%.It is standared that 1 kWh = 860 Kcal

25Problem 2.15: A diesel power station has following data:Fuel consumption/day = 1000kg; Units generated/day = 4000kWh Calorific value of fuel = 10,000 kcal/kg;Alternator efficiency = 96%; Engine Mech. Efficiency = 95%Estimate (i)Specific fuel consumption. (ii)Overall efficiency. (iii)Thermal efficiency of engine.It is standard that 1 kWh = 860 Kcal

26It is standard that 1 kWh = 860 Kcal

27Gas Turbine Power PlantThe generating station which employs gas turbine as the prime mover as the generation of electrical energy is known as a gas turbine power plant.Air is used as a working fluid*. Fuel pumped in and ignited to work with compressed air.Hot and high pressure gases from the combustion chamber passes through the gas turbine where it expands and do some mechanical work.The gas turbine drives the alternator which converts mechanical energy to electrical energy.Gas turbine power plant are being used as a standby plants for hydro electric stations, as a starting plant for driving auxiliaries in power plants.

* The air is compressed by the compressor and is led to the combustion chamber, where heat is added to the air thus rising its temperature.28Gas Turbine Power Plant (Cont.)AdvantagesIt is simple in design as compared to steam power station*.It is much smaller in size as compared to the steam power station of the same capacity.The initial and operating costs are much lower than the equivalent steam power station.It requires less water as no condenser is used.Low maintenance charges.Started quickly in cold conditions**.No standby losses**.DisadvantagesThere is a problem for starting the unit***.Net output is low. Since greater part of power developed by the turbine is used in driving the compressor.The overall efficiency of such a plant is low (about 20%). Because the exhaust gases from the turbine contain sufficient heat.The temperature of combustion chamber is quiet high (3000F). So that its life is comparatively reduced.

* Since no boiler and other auxiliaries are required.**In steam power station losses occurs because boiler is kept in operation when though the steam turbine is supplying no load.***Before starting turbine, the compressor has to be operated for which power is required from some external source. How ever once the unit is started. Then there is no need for the external power. As the turbine it self provide the necessary power for operation.29Schematic arrangement of Gas Turbine Power PlantCompressorRegeneratorCombustion ChamberGas TurbineAlternatorStarting Motor