Parameters for powerhouse dimensions

A powerhouse houses the turbines, generators, control and auxiliary equipment. Its plan dimensions and height are fixed mainly by the size and number of generating units.

Parameters for fixing the dimensions

1. Number, type and size of units: turbine type (Pelton, Francis, Kaplan), runner diameter, spiral casing size and generator diameter.
2. Length:
   • Unit spacing (centre to centre) = larger of spiral casing width or generator barrel diameter + clearance (about 1–2 m each side). For Pelton units, the distributor/manifold size governs.
   • Total length = number of units × unit spacing + erection (service) bay (about 1–1.5 unit spacing) + control/auxiliary room.
3. Width: governed by spiral casing and draft tube (Francis/Kaplan) or by turbine housing; plus space for main inlet valve, walkways, cable ducts and the overhead crane span.
4. Height:
   • Setting level of turbine from cavitation (Thoma σ) and tailwater level.
   • Draft tube depth below the runner (substructure).
   • Generator floor, and crane clearance high enough to lift the largest part (generator rotor) over other units.
5. Crane capacity and span (heaviest piece to lift).
6. Tailwater level and flood level: powerhouse floor above maximum flood; draft tube outlet submerged.
7. Auxiliaries: governors, control room, battery room, cooling water, transformers and switchyard space.
8. Site conditions: foundation geology, access road, space available (surface or underground).

Typical plan (Francis units)

 <-- erection --><-- unit --><-- unit --><ctrl>
     bay            bay 1       bay 2
+---------------+-----------+-----------+-----+
|               |  ( G1 )   |  ( G2 )   |     |
|  unloading,   |  spiral   |  spiral   | con-|
|  assembly     |  casing   |  casing   | trol|
|               |  MIV      |  MIV      |     |
+---------------+-----------+-----------+-----+
                  | draft tubes ->  tailrace