Things to Know About Power Generation Station Part 2

General Arrangement of Hydro-electric Plant

Though hydro-electric power station simply involves the conversion of hydraulic energy to

the mechanical energy, it requires many types of supporting arrangements. The Fig. 2 show s the

schematic  arrangement  of  hydro -electric  power  station  which  uses  water  supply  from  an

artificially constructed dam.

Fig. 2  Schematic arrangement of hydro-electric power plant

The dam is constructed across the river and water from catchment area is collected  behind

the wall of the dam, in high mountains. A pressure channel is taken from such a water reservoir

which takes water to a surge tank. The surge tank is a controlling room which controls the flow

of water i.e. adjusts the discharge of water according to   the need of the turbine and load on it.

Trash  rack  does  not  allow  floating  and  other  impurities  to  pass  to  the  turbine.  The  pressure

channels plays a very important role. It relieves the pressure on the penstocks when the turbine

valves  are  open  or  closed  suddenly.  The  water  is  then  taken  to  a  valve  house  from  where  the

penstocks start. The valve house contains main sluice valve and the automatic isolating valves.

These valves also regulate the flow of water to the power house and isolates the supply of water

if there  is any  emergency  such  as  bursting of a  penstock. Through the penstocks, the water  is

taken to the power house which consists of turbine and the alternator. The  penstocks are  nothing

but the steel pipes which are arranged in the form of open or  closed conduits, supported by the

anchor blocks.

When the water from the penstock is hammered through a nozzle, on the turbine blades, the

turbine starts rotating.  At this stage the  hydraulic energy  is converted to a mechanical energy.

The  turbine  drives  the  alternator  which  is  coupled  to  the  shaft  of  the  turbine.  The  alternator

converts  the  mechanical  energy  into  an  electrical  energy.  This  electrical  energy  is  then

transmitted to the load centers. The water collected from the turbine is called tail  race. This tail

race is then taken off to the river.

Let us discuss the constituent and their functions in the operation of the hydroelectric power

station.

Dam

The water reservoir in  the form of a dam is the main part of the power station. It stores the

water,  provides  the  continuous  supply  of  water  and  maintains  the  necessary  water  head.  The

dams are built up of stones and concrete. The design and type of the dam us selected according

to the topography of the site and economical aspects.

Spillways

There are certain times when the river flow exceeds the storage capacity of the dam, due to

the heavy rainfall. The spillways are provided to discharge this surplus water and mai ntain safe

water level in the dam.

Surge Tank

This is an important projecting device in a hydro-electric power plant. It is built just before

the valve house. It protects the penstocks from bursting due to sudden pressure changes.

If the load on the turbine is thrown off suddenly then by the governing action, the turbine

input gates get suddenly closed. Thus there is sudden stopping of water at the lower end of the

penstock. This time the excess water at the lower end of the penstock, rushes back to the surge

tank. The surge tank water level increases. Thus the penstock is protected from bursting due to

high pressure. The surge tank absorbs this high pressure swing by increasing its water level.

On  the  other  hand,  when  the  load  on  the  turbine  suddenly  increases,  the  additional  water

required is drawn from the surge tank. This satisfies the increased water demand instantly.

Thus the surge tank controls the pressure changes created due to rapid changes in the water

flow in penstock and hence protects the penstock from water hammer effects which might burst

the penstock.