Reservoir type hydropower plant schematic

A reservoir (storage) type hydropower plant has a high dam that stores water in a large reservoir, usually for seasonal use. Water stored in the wet season is released in the dry season, so the plant can supply firm and peaking power all year. Kulekhani-I (60 MW) is Nepal's main example.

Schematic

  Reservoir (FSL)  ~~~~~~~~~~~~
  ~~~~~~~~~~~~~~~ |\
  ~~~ storage ~~~ | \  High dam
  ~~~~~~~~~~~~~~~ |  \  + spillway
  Intake tower -->|===\=============\
  (MOL)           |____\             \ Headrace tunnel
                                 [Surge tank]
                                      |
                                      | Penstock
                                      v
                    Valve -> Turbine -> Generator
                               |          |
                          Draft tube   Transformer
                               |          |
                           Tailrace   Switchyard
                               v          v
                             River       Grid

Civil components

1. Dam: concrete gravity, arch or rockfill dam that creates head and storage. Full supply level (FSL) and minimum operating level (MOL) define the live storage.
2. Reservoir: stores water from the monsoon for the dry season; dead storage below MOL holds sediment.
3. Spillway: gated or ungated, passes the design flood safely.
4. Intake tower: draws water from various levels with trash rack and gates.
5. Headrace tunnel: pressure tunnel to the surge tank.
6. Surge tank: protects the tunnel from water hammer and supplies water on load rise.
7. Diversion tunnel/cofferdam (during construction), bottom outlet for emptying and flushing.
8. Powerhouse (surface or underground) and tailrace.

Mechanical components

1. Penstock with anchor blocks; main inlet valve (butterfly or spherical).
2. Turbine: Francis for medium head or Pelton for high head (Kulekhani uses Pelton).
3. Governor: keeps frequency constant by controlling flow.
4. Draft tube (reaction turbines), cooling water, oil and compressed air systems, EOT crane.

Electrical components

1. Synchronous generator with excitation system and AVR.
2. Generator circuit breaker and bus duct.
3. Step-up transformer and switchyard (breakers, isolators, CT, PT, lightning arresters).
4. Station service: station transformer, DC battery, diesel generator for black start.
5. Protection, control and SCADA; earthing mat.

Features

Reservoir plants give firm power, peaking and frequency regulation, but have high cost, long construction time, resettlement and sedimentation problems.