Power Plant Engineering

362 POWER PLANT ENGINEERING

of both surge tanks can be calculated independently according to the usual surge theory. If the prime
mover is reaction type, the oscillations in tailrace and headrace interfere with each other and, therefore,
the larger areas of surge tank is required than the volume required for surge tank used with impulsive
type prime mover.

The Santa Giustina power house in Italy is an example of this type of arrangement. Koyna power
project also comes under this class except there is no surge tank to the downstream side as the tailrace
tunnel is not very long.

4. Station arrangement without surge tank. If the pressure tunnel and tailrace tunnel are short
   in length, the upstream and downstream surge tanks can be eliminated from the system. The main points
   to be considered in this design are the maximum water hammer effect and danger of cavitations in the
   turbine. The latter can be eliminated by selecting the proper turbine axis level above the draft tube axis
   level.

A vertical or steep shafts (10 : 1) are provided to access the upstream or Swedish type power
house whereas horizontal or mild sloping tunnels prove more favourable. for downstream stations or
Alpine type layout.

Generally fresh air as supplied to the power house through the main access tunnel and warmed
up air is exhausted along the same tunnel through a separate duct. Sometimes separate air shafts are used
to exhaust the warmed up air.

The transformers and high voltage switching equipment were previously located outdoors al-
most without exception. In recent practice, transformers are also arranged underground in the trans-
former room excavated in the vicinity of power house. If the decision of the management is in the favour
of underground power house against air-raids, no significant gain could be achieved by locating the
transformer outdoor as it is one of the most sensitive and essential components of the power project. An
underground location of the transformer is further supported by the fact that the location of the trans-
former near the power house involves hardly any excess cost.

Draft tube

Power HouseClosureshaft

Transformer

Tailrace tunnel with expansion chamber

Accesstunnel

Cable shafts

Intake

Dam

Pressure shaft

Fig. 11.19

11.10 Prime-Movers

The prime-mover in the hydraulic power plant converts the energy of water into mechanical
energy and further into electrical energy. These machines are classified on the basis of the action of
water an moving blades.