Power Systems : Types of Various Power Plants

INTRODUCTION TO POWER PLANTS

Bulk electric power is produced by special plants known as generating stations or power plants. A generating station essentially employs a prime mover coupled to an alternator for the production of electric power. The prime mover (e.g., steam turbine, water turbine etc.) converts energy from some other form into mechanical energy. The alternator converts mechanical energy of the prime mover into electrical energy. The electrical energy produced by the generating station is transmitted and distributed with the help of conductors to various consumers.

Depending upon the form of energy converted into electrical, the generating stations are classified as under:

 1. Steam Power Station (Thermal Station):

A generating station which converts heat energy of coal combustion into electrical energy is known as a steam power station. A steam power station basically works on the Rankine cycle. Steam is produced in the roller by utilising the heat of coal combustion. The steam is then expanded in the prime mover (i.e., steam turbine) and is condensed in a condenser to be fed into the boiler again. The steam turbine drives the alternator which converts mechanical energy of the turbine into electrical energy.

This type of power station is suitable where coal and water are available in abundance and a large amount of electric power is to be generated.

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 irrespective of the existence of coal. 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.
5. The cost of generation is lesser than that of the diesel power station

Disadvantages:

1. It pollutes the atmosphere due to the production of large amount of smoke and fumes.
2. It is costlier in running cost as compared to hydroelectric plant.

The schematic diagram for the steam power plant is shown in figure below:

2.  Hydro-electric Power Station:

A generating station which utilizes the potential energy of water at a high level for the generation of electrical energy is known as a hydro-electric power station.

Hydro-electricity power stations are generally located in hilly areas where dams can be built conveniently, and large water reservoirs can be obtained.

In a hydro-electric power station, water head is created by constructing a dam across a river or lake. From the dam, water is led to a water turbine. The water turbine captures the energy in the falling water and changes the hydraulic energy (i.e., product of head and flow of water) in to mechanical energy at the turbine shaft. The turbine drives the alternator which converts mechanical energy into electrical energy.

Advantages:

1. It requires no fuel as water is used for the generation of electrical energy.
2. It is quite neat and clean as no smoke or ash is produced.
3. It requires very small running charges because water is the source of energy which is available free of cost.
4. It is comparatively simple in construction and requires less maintenance.
5. It does not require along starting time like as team power station.
6. It is robust and has a longer life.
7. They also help in irrigation and controlling floods.

Disadvantages:

1. It involves high capital cost due to construction of dam.
2. There is uncertainty about the availability of huge amount of water due to dependence on weather condition.
3. It requires high cost of transmission lines as the plants is located in hilly areas which are quite away from the consumers.

3.  Nuclear Power Station:

A generating station in which nuclear energy is converted into electrical energy is known as a nuclear power station. In nuclear power station, heavy elements such as Uranium (U²³⁵) or Thorium (Th²³²) are subjected to nuclear fission in a special apparatus known as a reactor. The heat energy thus released is utilised in raising steam high temperature and pressure. The steam runs the steam turbine which converts steam energy into mechanical energy. The turbine drives the alternator which converts mechanical energy into electrical energy.

The most important feature of a nuclear power station is that huge amount of electrical energy can be produced from a relatively small amount of nuclear fuel as compared to other conventional types of power stations.

It has been found that complete fission of 1 kg of Uranium (U²³⁵) can produce as much energy as can be produced by the burning of 4,500 tons of high-grade coal.

Advantages:

1. The amount of fuel required quite small. Therefore, there is a considerable saving in the cost of fuel transportation.
2. A nuclear power plant requires less space as compared to any other type of the same size.
3. It has low running charges as a small amount of fuel is used for producing bulk electrical energy.
4. This type of plant is very economical for producing bulk electric power.
5. It can be located near the load centres because it does not require large quantities of water and need not be near coal mines. Therefore, the cost of primary distribution is reduced.
6. There are large deposits of nuclear fuels available all over the word Therefore, such plants Can ensure continued supply of electrical energy for thousands of years.
7. It ensures reliability of operation.

Disadvantages:

1. The fuel used is expensive and is difficult to recover.
2. The capital cost on a nuclear plants very high as compared to other types of plants.
3. The erection and commissioning of the plant requires greater technical knowledge.
4. The fission by-products are generally radioactive and may came a dangerous amount of radioactive pollution.
5. Maintenance charges are high due to lack of standardization.
6. Nuclear power plants are not well suited for varying loads as the reactor does not respond to the load fluctuation efficiently.
7. The disposal of the by-products, which are radioactive, is a big problem. They have either to be disposed off in a deep trench or in a sea away from seashore.

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