Underground power stations:
Underground power stations are in danger of falling rocks and snow avalanches. It is a valley from the site for a hydro power plant. Underground power stations are built under special circumstances Availability of underground hard rock of suitable depth and desired location. Terror of bombs and air attacks. Frequent earthquakes.
Types of Underground Power Stations
Different types of underground power stations depend on position of head race and tail race, control valves, turbine and generator used, control room topography and geology etc.
- Free level tailrace tunnel without a downstream surge tank
- Downstream station
- Intermediate station arrangement
Advantages:
- They allow greater operating heads. Thus improves power output and efficiency
- They are safe against bomb attacks.
- They are safe against rock and earth slips or snow avalanches.
- The penstock and surge tanks may be cut into rock since the excavation is in the hard rock
- The cost of construction of power house and its erection is less
- It does not affect the scenic beauty of the site.
Disadvantages:
- Cost of construction of the power station and accessories is high.
- It requires increased lighting, special ventilation and air conditioning, thus it increases technical requirement and cost
- The construction of an additional tail race channel and downstream surge tank works out to be costly.
- Underground location of electrical equipment adds further to the cost.
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