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

Intentionally Left BlankIntentionally Left Blank

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)

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

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

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

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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Generating Stations

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