Generating Stations
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Transcript of Generating Stations
CONTENTS
1 Generating Stations
2 Steam Power Station (Thermal Station)
3 Schematic Arrangement of Steam Power Station
4 Choice of Site for Steam Power Stations
5 Efficiency of Steam Power Station
6 Equipment of Steam Power Station
7 Hydro-electric Power Station
8 Schematic Arrangement of Hydroelectric Power Station
9 Choice of Site for Hydro-electric Power Stations
10 Constituents of Hydro-electric Plant
11 Diesel Power Station
12 Schematic Arrangement of Diesel Power Station
13 Nuclear Power Station
14 Schematic Arrangement of Nuclear Power Station14 Schematic Arrangement of Nuclear Power Station
15 Selection of Site for Nuclear Power Station
16 Gas Turbine Power Plant
17 Schematic Arrangement of Gas Turbine Power Plant
18 Comparison of the Various Power Plants
1. Selection and placing of power-generating equipment
It should be such that t o get maximum return from a minimum of expenditure over the working life of the plant.
It Should be such so as to provide cheap, reliable andcontinuous service.
plant.
2.Operation of the plant
Generating Stations
Main parts of the generating stations are:
1. Prime mover
2. Alternator
Depending upon the form of energy converted into electrical Depending upon the form of energy converted into electrical energy, the generating stations are classified as under :
1. Steam power stations
2. Hydroelectric power stations
3. Diesel power stations
4. Nuclear power stations
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The electric generator
Steam Power Station (Thermal Station)
Converts heat energy of coal combustion into electrical energy.
•Working principle based on the Rankine cycle.
http://energy.sdsu.edu/testhome/vtAnimations/animations/chapter09/A-steamPower/basicRankineCycle.html
•Steam is produced in the boiler by coal combustion.
•Steam is then expanded in the prime mover / steam turbine.
•Steam is condensed in a condenser to be fed into the boiler again
This type of power station is suitable where coal and water are available in abundance.
Advantages
1. The fuel (i.e., coal) used is quite cheap.
2.Less initial cost as compared to other generating stations.
3.It can be installed at any place. The coal can be transported to
the site of the plant by rail or road.
4. It requires less space as compared to the hydroelectric power
station.station.
5. The cost of generation is lesser than that of the diesel power
station.
Disadvantages
1. It pollutes the atmosphere from smoke and fumes.2. It is costlier in running cost as compared to hydroelectric plant
Schematic Arrangement of Steam Power Station
The whole arrangement can be divided into the following stages :
1. Coal and ash handling arrangement
2. Steam generating plant
3. Steam turbine
4. Alternator
5. Feed water
6. Cooling arrangement
Choice of Site for Steam Power Stations
following points should be considered while selecting a sitefor a steam power station :
1. Supply of fuel
2. Availability of water
3.Transportation facilities3.Transportation facilities
4.Cost and type of land
5.Nearness to load centres
6.Distance from populated area.
Efficiency of Steam Power Station
The overall efficiency of a steam power station is quite low (about 29%) due mainly to two reasons.
1. Huge amount of heat is lost in the condenser (50% of total heat of combustion is lost in the condenser)
2. heat losses occur at various stages of the plant
Thermal efficiency:
ηthermal
Heat equivalent of mech. energytransmitted to turbine shaft=
Heat of coal combustion
Overall efficiency:
ηoverallHeat equivalent of electrical output
=
Heat of coal combustion
It may be seen that overall efficiency is less than the thermal efficiency. This is expected since some losses (about 1%) occur in the alternator.
( Equipment of Steam Power Station , Book Principles of power system , page #14)
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Hydro-electric Power Station
Utilizes the potential energy of water at a high level for the generation of electrical energy.
•Generally located in hilly areas
•Water head is created by constructing a dam
•water is led to a water turbine which drives the alternator and converts mechanical energy into electrical energy
Hydro-electric power stations are becoming very popular because the reserves of fuels (i.e., coal and oil) are depleting day by day.
They have the added importance for flood control, storage of water for irrigation and water for drinking purposes.
Advantages
1. Requires no fuel
2. Neat and clean
3. Very small running charges
4. Less starting time4. Less starting time
5. Robust and has a longer life
6. Multi purposes, irrigation and controlling floods
7. Less experienced persons may do the job well
Disadvantages
1. High capital cost due to construction of dam
2. Availability of water depends on weather conditions.
3. Skilled and experienced hands are required to build the plant.
4. High cost of transmission lines as the plant is located in hilly areas
Schematic Arrangement of Hydro-electric Power Station
•Catchment area collects at the back of the dam to form a reservoir
•Pressure tunnel is taken off from the reservoir and water brought to the valve house at the start of the penstock
•The valve house contains main sluice valves and automatic isolating valves.isolating valves.
The main sluice valves controls the water flow to the power houseThe automatic isolating valves cuts off supply of water when the penstock bursts
•A huge steel pipe known as penstock takes the water from valve house to turbine.
•A surge tank (open from top) is built just before the valve house and protects the penstock from bursting in case the turbine gates suddenly close due to electrical load being thrown off.
Sudden stopping of water at the lower end of the penstock causes it to burst like a paper log
The surge tank absorbs this pressure swing by The surge tank absorbs this pressure swing by increase in its level of water
Choice of Site for Hydro-electric Power Stations
1.Availability of water
2.Storage of water.
•Plants should be built at a place where adequate water is available at a good head.
•The storage helps in equalising the flow of water
3.Cost and type of land.
4. Transportation facilities.
•The land available at a reasonable price.
•Bearing capacity of the ground to withstandthe weight of heavy equipment
•Should be accessible by rail and road
Constituents of Hydro-electric Plant
The constituents of a hydro-electric plant are:
1. Hydraulic structures
2. Water turbines
3. Electrical equipment
Hydraulic structures in a hydro-electric power station include:
1. Dam2. Spillways3. Headworks4. Surge tank5. Penstock 6. Accessory works
Water turbines consist of following principal types.
1.Impulse turbines
2. Reaction turbines
a) Francis turbines
b) Kaplan turbines
The electrical equipment of a hydro-electric power station includes:1. Alternators2. Transformers3. Circuit breakers 4. Switching and protective devices
= m/sec2 x m3× kg / m3 x m x ηoverall
= m/sec2 x kg x m=Force x distance = joule (mul and div by sec)
=(joule/ sec) x Sec=Watt . sec=Watt . sec
Example # 2.6 , 7, 8,9
Or
= m/sec2 x m3/sec × kg / m3 x m x ηoverall
= (m/sec2 x kg x m)/sec=(Force x distance) /sec =(joule/ sec) =Watt
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Diesel Power Station
Diesel engine is used as the prime mover for the generation of electrical energy
Generation cost is considerable due to high price of dieselTherefore, such power stations are only used to produce small power.
Favorable at places where demand of power is less
used as standby sets for continuity of supply to important points such as:1. Hospitals2. Radio stations3. Cinema houses 4. Telephone exchanges
Advantages
1. The design and layout of the plant are quite simple.
2. Occupies less space
3. Can be located at any place.
4. Started quickly and can pick up load in a short time.
5. No standby losses.5. No standby losses.
6. Requires less quantity of water for cooling.
7. Cost is much less than that of steam power station.
8. The thermal efficiency is higher than steam power station.
9. Requires less operating staff.
Disadvantages
1. High running charges as the fuel used is costly.
2. Work unsatisfactorily under overload conditions .
3. Can only generate small power.
4. The cost of lubrication is generally high.4. The cost of lubrication is generally high.
5. The maintenance charges are generally high
1. Fuel supply system
2. Air intake system
3. Exhaust system
4. Cooling system
Schematic Arrangement of Diesel Power Station
4. Cooling system
5. Lubricating system
6. Engine starting system
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Nuclear Power Station
Generating station in which nuclear energy is converted into electrical energy
Uranium (U235) or Thorium (Th232) are subjected to nuclear fission in a special apparatus known as a reactor.
Heat energy thus released is utilised in raising steam at high
1 kg of Uranium (U235) can produce same energy as by the burning of 4,500 tons of high grade coal.
The breaking up of nuclei of heavy atoms into two nearly equal parts with release of huge amount of energy is known as nuclear fission
Fission:
Heat energy thus released is utilised in raising steam at high temperature and pressure
Advantages
1.The amount of fuel required is quite small.
2. Requires less space .
3. Low running charges .
4. Very economical for producing bulk electric power.
5. Can be located near the load centres
6. There are large deposits of nuclear fuels available all over
the world. Therefore, such plants can ensure continued
supply of electrical energy for thousands of years.
7. Ensures reliability of operation.
Disadvantages
1. The fuel used is expensive and is difficult to recover.
2.The capital cost on a nuclear plant is very high.
3. Commissioning of plant requires greater technical know-how.
4. By-products are generally radioactive and may cause a
radioactive pollution.radioactive pollution.
5. Maintenance charges are high due to lack of standardisation.
6. Not well suited for varying loads .
7. The disposal of the by-products, which are radioactive, is a big
problem.
Arrangement can be divided into the following main stages :
1. Nuclear reactor
2. Heat exchanger
Schematic Arrangement of Nuclear Power Station
2. Heat exchanger
3. Steam turbine
4. Alternator
http://www.animatedsoftware.com/environm/nukequiz/nukequiz_one/nuke_parts/reactor_parts.swf
1. Nuclear reactor:•Controls the chain reaction that starts once the fission is done.
•Explosion can occur if chain reaction is not controlled.
A nuclear reactor is a cylindrical stout pressure vessel and houses:1. Fuel rods of Uranium2. Moderator3. Control rods
Fuel rods of Uranium
•Contains fission material and release huge amount of energy when bombarded with slow moving neutrons.
Moderator•Graphite rods which enclose the fuel rods.
•Slows down the neutrons before they bombard the fuel rods.
•Cadmium rods are inserted into the reactor.
Control rods
•Cadmium is strong neutron absorber and thus regulates the supplyof neutrons for fission.
2. Heat exchanger
•The coolant gives up heat to the heat exchanger which is utilized in raising the steam.
•After giving up heat, the coolant is again fed to the reactor.
3. Steam turbine.
•The steam produced in the heat exchanger is led to the •The steam produced in the heat exchanger is led to the steam turbine through a valve.
4. Alternator.
•The steam turbine drives the alternator which converts mechanical energy into electrical energy.
Selection of Site for Nuclear Power Station
The following points should be kept in view while selecting the site for a nuclear power station :
1. Availability of water
2. Disposal of waste
3. Distance from populated areas
4. Transportation facilities
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Gas Turbine Power Plant
Generating station which employs gas turbine as the prime mover for the generation of electrical energy.
The hot and high pressure air from the combustion chamber is then passed to the gas turbine where it expands and does the mechanical work.
Compressor, gas turbine and the alternator are mounted on the same shaft.
so that a part of mechanical power of the turbine can be utilized for the operation of the compressor.
Used as standby plants for hydro-electric stations for driving auxiliaries.
Advantages
1. Simple in design, no boilers and their auxiliaries
2. smaller in size
3. Lower initial and operating costs
4.Requires less water as no condenser is used.
5. Maintenance charges are quite small
6. Turbines are much simpler in construction and operation
7. Started quickly form cold conditions
8. No standby losses
Disadvantages
1. Before starting the turbine, the compressor has to be operated for which power is required from some external source.
2. Net output is low as power developed by the turbine is used in driving the compressor.
3. Overall efficiency of such plants is low (about 20%)3. Overall efficiency of such plants is low (about 20%)
4. Less life of combustion chamber
Schematic Arrangement of Gas Turbine Power Plant
The main components of the plant are :
1. Compressor
2. Regenerator
3. Combustion chamber
4. Gas turbine
5.Alternator
6. Starting motor
(Comparison of the Various Power Plants, Book Principles of power system , page #37)
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