Generating Stations

Generating Stations:

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.  It may be emphasized here that apart from prime mover-alternator combination,a modern generating station employs several auxiliary equipment and instruments to ensure cheap,reliable and continuous service.Depending upon the form of energy converted into electrical energy, the generating stations are classified as under :

(i) Steam power stations 

(ii) Hydro-electric power stations

(iii) Diesel power stations 

(iv) Nuclear power stations

In this modern world, the dependence on electricity is so much that it has become a part and parcel of our life.The ever increasing use of electric power for domestic, commercial and industrial purposes necessitates to provide bulk electric power economically.This is achieved with the help of suitable power producing units, known as  Power plants or Electric power generating stations.The design of a power plant should incorporate two important aspects.Firstly, the selection and placing of necessary power-generating equipment should be such so that a maximum of return will result from a minimum of expenditure over the working life of the plant. Secondly, the operation of the plant should be such so as to provide cheap, reliable and continuous service.

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 boiler by utilizing 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:

(i) The fuel ( i.e., coal) used is quite cheap.

(ii) Less initial cost as compared to other generating stations.

(iii) 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.

(iv) It requires less space as compared to the hydroelectric power station.

(v) The cost of generation is lesser than that of the diesel power station.

Disadvantages:

(i) It pollutes the atmosphere due to the production of large amount of smoke and fumes.

(ii)  It is costlier in running cost as compared to hydroelectric plant.

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-electric 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) into mechanical energy at the turbine shaft.  The turbine drives the alternator which 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:

(i) It requires no fuel as water is used for the generation of electrical energy.

(ii) It is quite neat and clean as no smoke or ash is produced.

(iii) It requires very small running charges because water is the source of energy which is avail-able free of cost.

(iv) It is comparatively simple in construction and requires less maintenance.

(v) It does not require a long starting time like a steam power station.  In fact, such plants can be put into service instantly.

(vi) It is robust and has a longer life.

(vii) Such plants serve many purposes.  In addition to the generation of electrical energy, they also help in irrigation and controlling floods.

(viii) Although such plants require the attention of highly skilled persons at the time of construction, yet for operation, a few experienced persons may do the job well.

Disadvantages:

(i) It involves high capital cost due to construction of dam.

(ii) There is uncertainty about the availability of huge amount of water due to dependence on weather conditions.

(iii) Skilled and experienced hands are required to build the plant.

(iv) It requires high cost of transmission lines as the plant is located in hilly areas which are quite away from the consumers.

3-Diesel Power Station:

A generating station in which diesel engine is used as the prime mover for the generation of electrical energy is  known as   diesel power station.In a diesel power station, diesel engine is used as the prime mover. The diesel burns inside the engine and the products of this combustion act as the “working fluid” to produce mechanical energy. The diesel engine drives the alternator which converts mechanical energy into electrical energy. As the generation cost is considerable due to high price of diesel, therefore, such power stations are only used to produce small power.Although steam power stations and hydro-electric plants are invariably used to generate bulk power at cheaper cost, yet diesel power stations are finding favour at places where demand of power is less, sufficient quantity of coal and water is not available and the transportation facilities are inadequate.  These plants are also used as standby sets for continuity of supply to important points such as hospitals, radio stations, cinema houses and telephone exchanges.

Advantages:

(i) The design and layout of the plant are quite simple.

(ii) It occupies less space as the number and size of the auxiliaries is small.

(iii) It can be located at any place.

(iv) It can be started quickly and can pick up load in a short time.

(v) There are no standby losses.

(vi) It requires less quantity of water for cooling.

(vii) The overall cost is much less than that of steam power station of the same capacity.

(viii) The thermal efficiency of the plant is higher than that of a steam power station.

(ix) It requires less operating staff.

Disadvantages:

(i) The plant has high running charges as the fuel ( i.e ., diesel) used is costly.

(ii) The plant does not work satisfactorily under overload conditions for a longer period.

(iii) The plant can only generate small power.

(iv) The cost of lubrication is generally high.

(v) The maintenance charges are generally high.

4-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 utilized in raising steam at 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. Al-though the recovery of principal nuclear fuels(i.e ., Uranium and Thorium) is difficult and expensive,yet the total energy content of the estimated world reserves of these fuels are considerably higher than those of conventional fuels,  viz., coal, oil and gas. At present, energy crisis is gripping us and, therefore, nuclear energy can be successfully employed for producing low cost electrical energy on a large scale to meet the growing commercial and industrial demands.

Advantages:

(i) The amount of fuel required is quite small.  Therefore, there is a considerable saving in the cost of fuel transportation.

(ii) A nuclear power plant requires less space as compared to any other type of the same size.

(iii) It has low running charges as a small amount of fuel is used for producing bulk electrical energy.

(iv) This type of plant is very economical for producing bulk electric power.

(v) It can be located near the load centers because it does not require large quantities of water and need not be near coal mines.  Therefore, the cost of primary distribution is reduced.

(vi) 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.

(vii) It ensures reliability of operation.

Disadvantages:

(i) The fuel used is expensive and is difficult to recover.

(ii) The capital cost on a nuclear plant is very high as compared to other types of plants.

(iii) The erection and commissioning of the plant requires greater technical know-how.

(iv) The fission by-products are generally radioactive and may cause a dangerous amount of radioactive pollution.

(v) Maintenance charges are high due to lack of standardization.  Moreover, high salaries of specially trained personnel employed to handle the plant further raise the cost.

(vi) Nuclear power plants are not well suited for varying loads as the reactor does not respond to the load fluctuations efficiently.

(vii) 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 sea-shore.