Page 295 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

ii Super heater: The steam produced in the boiler is wet and is passed through a super heater where it is
dried and super heated by the flue gases on their way to chimney. Superheating provides two principal
benefits. Firstly, the overall efficiency is increased. Secondly, too much condensation in the last stages of
turbine (which would cause blade corrosion) is avoided. The super heated steam from the super heater is
fed to steam turbine through the main valve.
iii Economiser: An economiser is essentially a feed water heater and derives heat from the flue gases
for this purpose. The feed water is fed to the economiser before supplying to the boiler. The economiser
extracts a part of heat of flue gases to increase the feed water temperature.
iv Air preheater: An air preheater increases the temperature of the air supplied for coal burning by deriving
heat from flue gases. Air is drawn from the atmosphere by a forced draught fan and is passed through
air preheater before supplying to the boiler furnace. The air preheater extracts heat from flue gases and
increases the temperature of air used for coal combustion.

3 Steam turbine
The dry and super heated steam from the super heater is fed to the steam turbine through main valve. The heat
energy of steam when passing over the blades of turbine is converted into mechanical energy. After giving heat
energy to the turbine, the steam is exhausted to the condenser which condenses the exhausted steam by means
of cold water circulation.
4 Alternator

The steam turbine is coupled to an alternator. The alternator converts mechanical energy of turbine into electrical
energy. The electrical output from the alternator is delivered to the bus bars through transformer, circuit breakers
and isolators.
5 Feed water
The condensate from the condenser is used as feed water to the boiler. Some water may be lost in the cycle which
is suitably made up from external source. The feed water on its way to the boiler is heated by water heaters and
economiser. This helps in raising the overall efficiency of the plant.
6 Cooling arrangement

In order to improve the efficiency of the plant, the steam exhaust from the turbine is condensed by means of a
condenser. Water is drawn from a natural source of supply such as a river, canal or lake and is circulated through
the condenser. The circulating water takes up the heat of the exhausted steam and itself becomes hot. This hot
water coming out from the condenser is discharged at a suitable location down the river. In case the availability of
water from the source of supply is not assured throughout the year, cooling towers are used. During the scarcity
of water in the river, hot water from the condenser is passed on to the cooling towers where it is cooled. The cold
water from the cooling tower is reused in the condenser.
A modern steam power station is highly complex and has numerous equipment and auxiliaries. However, the
most important constituents of a steam power station are
1 Steam generating equipment

2 Condenser
3 Prime mover
4 Water treatment plant
5 Electrical equipment

Steam generating equipment - This is an important part of steam power station. It is concerned with the
generation of superheated steam and includes such items as boiler, boiler furnace, super heater, economiser, air
pre-heater and other heat reclaiming devices

Boiler - A boiler is closed vessel in which water is converted into steam by utilising the heat of coal combustion.
Steam boilers are broadly classified into the following two types:
a Water tube boilers

b Fire tube boilers

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CITS : Power - Electrician & Wireman - Lesson 106-116