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
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
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.
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.
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