Power Plant Engineering

HYDRO-ELECTRIC POWER PLANTS 355

load, this energy will be released by allowing the water to flow from the head water pond through the
water turbine of the pumped storage plant. These plants can be used with hydro, steam and i.e. engine
plants. This plant is nothing but a hydraulic accumulator system and is shown in Fig. 11.9. These plants
can have either vertical shaft arrangement or horizontal shaft arrangement. In the older plants, there
were separate motor driven pumps and turbine driven generators. The improvement was the pump and
turbine on the same shaft with the electrical element acting as either generator or motor. The latest
design is to use a Francis turbine which is just the reverse of centrifugal pump. When the water flows
through it from the head water pond it will act as a turbine and rotate the generator. When rotated in the
reverse direction by means of an electric motor, it will act as a pump to shunt the water from the tail
water pond to the head water pond.

Head

Race

Head

Water

Pond

Penstock

Power House with

Turbine & Pumps

Ta i l W a t e r

Pond

Ta i l R a c e

Fig. 11.9
The efficiency of such a plant is never 100 per cent. Some water may evaporate from the head
water pond resulting in the reduction in the stored energy or there might be run off through the soil.

11.9 Power House and Turbine Setting

According to the location of the hydel power station, the power houses are classified as surface
power house or underground power house. As the name implies, the underground power house is one
which is built underground. A cavity is excavated inside earth surface where the sound rock is available
to house the power station. A surface power house is one which is founded on earth’s surface and its
superstructure rests on the foundation.

The surface power house has been broadly divided into three subdivisions which is separated
from the intake as mentioned below :

(a) Substructure ; (b) Intermediate structure ; (c) Super-structure.
(a) Substructure. The substructure of a power-house is defined as that part which extends from
the top of the draft tube to the soil or rock. Its purpose is to house the passage for the water coming out
of the turbine. In case of reaction turbines, the hydraulic function of the sub-structure is to provide a
diverging passage (known as draft tube) where the velocity of the exit water is gradually reduced in
order to reduce the loss in pushing out the water. In case of impulse turbine, such a draft tube is not
required and only an exit gallery would serve the purpose.