Power Plant Engineering

Fig. 11.12
Fig. 11.13
Underground Power House. The conven-
tional hydro-electric power stations are usually lo-
cated over-ground at the foot of a dam or a hill slope
on the banks of a river. The first underground power
station Nerayaz was built in 1897 in Switzerland.
The high capacity underground power plants were
built only after second world war. The idea of locat-
ing powerhouse underground was suggested not only
with the intention of protecting them against air raids
but also technical and economical considerations
were mainly considered. After second world war,
the immunity against air attacks was unquestionably regarded as an important. advantage-of under-
ground power station. A large number of underground power stations have been installed in U.K., U.S.A.,
Russia, Canada, Japan after second world war and recently in India also.
In all, there are about 300 such stations in service with a total installed capacity of 31 million kW
Fig. 11.15. Horizontal setting of Pelton wheel with penstock upto the end of 1963.
 Fig. 11.15
Head race
Super structure
Generator
Prime
mover
Draft tube
Tail box
Screens
Head race
Steel
Penstock
Prime
mover
Tail race
Draft
tube
Generator
Super structure
Super structure
Alternator
Tailrace
Kaplan
Turbine
Guide
vane
Penstock
Draft tube
Crane
Fig. 11.14

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HYDRO-ELECTRIC POWER PLANTS
359
The considerations supporting the construction of underground power stations are stated below :
1. Non-availability of a suitable site for a conventional surface station and good slope for penstock.
2. Danger of falling rocks and snow avalanches particularly in narrow valleys.
3. Availability of underground sound rock and avoidance of a long pressure tunnel and facility
for a convenient tail-race outlet.
4. Possibility of elimination of surge tank required for surface station due to long pressure tun-
nel
5. The rugged topographical features and the difficulties in finding a suitable short and steep
slope for pipe lines make it more economical to install the water conduit, the machine, trans-
former hall and tailrace system underground.
6. Foundation costs for overground power house become excessive in case of poor quality sur-
face layers. The construction of draft tube, spiral case and separating floors in loose weath-
ered rock is again more expensive than the excavation of corresponding parts underground.
The costs of underground machine hall are lower than those of the superstructure of a surface
powerhouse of similar dimensions.