1. Under suitable geological conditions, the underground conduit may prove the shortest and
sometimes even straight. The power conduit may be much shorter than the length of power
canal used for underground power house as the power canal usually built to follow the con-tours of the terrain. By locating the power house underground, the number of restrictions as
safe topographical and geological conditions along the penstock and sufficient space at the
foot of the hill for constructing the power house are completely eliminated.
2. The construction of underground conduit instead of penstock results in considerable saving
in steel, the internal pressure is carried partly by the rock if it is of good quality. In sound high
quality rock, the penstock is replaced by an inclined or vertical pressure shaft excavated in
rock and provided with a steel lining of greatly reduced thickness in comparison with ex-posed penstock ‘roe purpose’ of lining in such cases is protection against the seepage losses.
3. The reduced length of the pressure conduit reduced the pressures developed due to water-hammer. Therefore, smaller surge tank is also sufficient.
4. For the economical arrangement, the ratio of the pressure conduit to the tail-race tunnel is
also significant. The overall cost of the system is lower if the tail-race tunnel length is rela-tively large.
5. The construction work at underground power station can continue uninterrupted even under
severest winter conditions. The overall construction cost and period of construction is re-duced due to continuity of work.