Hydropower plant components and functions

A hydropower plant converts the potential energy of water stored at a height into electrical energy. Its components fall into three groups: civil (to collect and carry water), mechanical (to convert water energy to shaft power) and electrical (to generate and deliver power).

 Reservoir/River
   | Dam or weir + intake
   v
 Headrace (canal/tunnel) -> Surge tank/forebay
   v
 Penstock -> Turbine -> Generator -> Transformer -> Grid
   |
 Draft tube -> Tailrace -> River

Civil components

1. Dam or diversion weir: creates head and/or storage and diverts water into the intake.
2. Intake: entry structure with trash rack and gates; controls flow and keeps out debris.
3. Gravel trap and desander: remove coarse and fine sediment to protect the turbines.
4. Headrace canal or tunnel: carries water to the forebay or surge tank with minimum head loss.
5. Forebay / surge tank: forebay is a small pond feeding the penstock; surge tank absorbs water hammer pressure rise and supplies water on sudden load rise.
6. Spillway: passes flood water safely over or around the dam.
7. Powerhouse building: houses the units, cranes and control room.
8. Tailrace: returns water to the river.

Mechanical components

1. Penstock: steel pressure pipe carrying water to the turbine.
2. Main inlet valve: butterfly (low/medium head) or spherical (high head) valve to isolate the turbine.
3. Turbine: Pelton, Francis or Kaplan, converts hydraulic energy into rotating mechanical energy.
4. Governor: controls wicket gates or needle to keep speed constant as load changes.
5. Draft tube: (reaction turbines) recovers kinetic energy at runner exit and allows setting above tailwater.
6. Auxiliaries: cooling water, oil pressure unit, compressed air, crane, drainage and dewatering.

Electrical components

1. Generator: synchronous machine coupled to the turbine; produces power at e.g. 11 kV.
2. Excitation system and AVR: supply DC to the rotor and control terminal voltage and reactive power.
3. Generator circuit breaker and bus: switching and isolation of the unit.
4. Generator step-up transformer: raises voltage (e.g. 11/132 kV) for transmission.
5. Switchyard: breakers, isolators, CTs, PTs, lightning arresters and busbars.
6. Station auxiliaries: station transformer, DC battery system, diesel generator for black start.
7. Protection, control and SCADA: relays, metering and remote monitoring.