Page 293 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

MODULE 18 : Generation, Transmission and Distribution

LESSON 106-116 : Source of energy - thermal power
generation, hydro and nuclear power station

Objectives

At the end of this lesson you shall be able to:
• explain conventional and energy source and state the various source of energy
• explain the working of hydroelectric power station
• explain the working of steam power station
• explain the working of nuclear power station
• explain the working of diesel power station.

Generation of electrical energy
Demand of an electrical system
The total power drawn by the customer of a large utility system fluctuates between wide limits depending on
the seasons and time of the day. If we plot the duration of each demand on an annual base, we obtain the load
duration curve. The demand of power give rise to three types of generating stations.
1 Base power stations: Base power stations deliver full power at all times: Nuclear stations and coal fired
stations are particularly well adapted to furnish base demand.
2 Intermediate power stations: Intermediate power stations that can respond relatively quickly to changes in
demand, usually adding or removing one or more generating units. Hydro power stations are well adapted for
this purpose.
3 Peak generating stations: Peak generating stations that deliver power for brief intervals during the day. Such
stations must be put into service very quickly.
Consequently, they are equipped with prime movers such as diesel engines, gas turbines, compressed air motors
that can be started up in a few minutes. In this regard it is worth mentioning that thermal generating stations
using gas or coal take from 4 to 8 hours to start up, while nuclear stations may take several days. Obviously such
generating stations cannot be used to supply short term peak power.

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 station

Steam power 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.
(Fig 1)
Advantages
1 The fuel 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.

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