Page 296 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Water treatment plant - Boilers require clean and soft water for longer life and better efficiency. However, the
source of boiler feed water is generally a river or lake which may contain suspended and dissolved impurities,
dissolved gases etc. Therefore, it is very important that water is first purified and softened by chemical treatment
and then delivered to the boiler. The water from the source of supply is stored in storage tanks. The suspended
impurities are removed through sedimentation, coagulation and filtration. Dissolved gases are removed by
aeration and degasification. The water is then ‘softened’ by removing temporary and permanent hardness through
different chemical processes. The pure and soft water thus available is fed to the boiler for steam generation.

Electrical equipment - A modern power station contains numerous electrical equipment. However, the most
important items are:
i Alternators: Each alternator is coupled to a steam turbine and converts mechanical energy of the turbine
into electrical energy. The alternator may be hydrogen or air cooled. The necessary excitation is provided by
means of main and pilot exciters directly coupled to the alternator shaft.

ii Transformers: A generating station has different types of transformers, viz.,
a main step-up transformers which step-up the generation voltage for transmission of power.
b station transformers which are used for general service (e.g., lighting) in the power station.
c auxiliary transformers which supply to individual unit-auxiliaries.
iii Switchgear: It houses such equipment which locates the fault on the system and isolate the faulty part from
the healthy section. It contains circuit breakers, relays, switches and other control devices
Hydroelectric power station (Fig 2)
Generating station which utilises 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 available 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.

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