Types of powerhouses and suitability

A powerhouse houses the turbines, generators, governors, control and auxiliary equipment. Types are classified by position relative to the ground.

1. Surface (open-air) powerhouse

Built on the ground surface, at the end of the penstock or at the dam toe.

  Penstock
      \
       \   +-------------+
        \  |  Generator  |
         \ |    floor    |
 ground   \|_____________|
 ~~~~~~~~~~|  Turbine    |~~~ tailrace
           |_draft tube__|

Variants: dam-toe / dam-integral (at the foot of or inside a gravity dam, short penstock), river-bed / in-stream (low head run-of-river; the powerhouse forms part of the weir), and canal/penstock-end (conventional, away from the dam).

Suitable where: rock or soil of good bearing capacity near the surface, gentle topography, no landslide, rockfall or flood risk, low to medium head, and cost advantage.

2. Semi-underground (partly buried) powerhouse

The substructure is in an excavated pit or shaft with the superstructure at ground level.

Suitable where: good rock at depth but steep or unstable surface, where the draft tube lies deep, or where protection from floods or snow is needed.

3. Underground (cavern) powerhouse

A large cavern excavated in sound rock, linked by a pressure shaft, access tunnel and tailrace tunnel.

 Surface
 ======= switchyard
   |  cable/vent shaft
   |     ___________
   |    | Generator |   Cavern
 Pressure| Turbine   |   (rock)
 shaft --|___________|--- tailrace tunnel
 access tunnel (adit)

Suitable where: high head and steep valleys, very high rock cover, landslide/avalanche or flood-prone surface, severe climate, security reasons, or where surface land is limited; also for large pumped-storage schemes. Needs good rock and higher investment.

Comparison