Components of a Run-of-River Mini-Hydro Station

1. The Weir Structure

Typically, the weir is a relatively small dam that diverts water from the river to the power station. It must be built in compliance with the provisions of RA 7156 (the Mini-Hydro Development Incentive Act) and RA 9513, the New Renewable Energy Act, which specifies such types of diversion structures in  order to qualify for the government incentives available. These provisions include the type of construction allowed; provisions for fish pass channels; overflow spillways etc.

2. HEADRACE LINE

The headrace line is part of each mini- hydropower system whose function is to convey water from the intake of the weir to the surge tank or forebay which stores the water before it is fed into the power station itself.
The headrace line is the low pressure component of the system as flow inside the conduit is initiated at the start by the head from the weir crest to the intake where thereafter, flow is caused by gravity. Often, the headrace is an open canal or conduit channel, although it is sometimes necessary to use a pipeline.

3. SURGE TANK OR FOREBAY

The surge tank provides relief from upsurge pressure in the event of instantaneous or rapid closing of the intake valve before the turbines.
The purpose of the outer tank is to provide the source of water to the penstock with sufficient pressure for the flow of water from the weir’s intake.

4. PENSTOCK LINE

The penstock line is the high pressure component of the system. It is the pipeline which delivers the water flow at high velocity to the turbines to turn its runner or wheels which is directly connected to the generator, eventually producing power. As such, it is normally set up on a steep pitch to the power house, as shown, to create high pressure to run the turbines.

5. POWERHOUSE AND TAILRACE

The powerhouse contains the turbine/generator sets and other electrical equipment and has two (2) distinct components, viz:

• Super structure, consisting of the portion of the powerhouse above finished ground level whose primary function is to protect the electrical equipment units from all negative elements of weather and security threats;
• Sub-structure, consisting of the massive first and second stage concrete below ground level serving as foundation for the turbines/generator sets and component parts.

6. ELECTRO-MECHANICAL WORKS

Electro-Mechanical works consist of the following principal components

1. Turbines which in all cases for each of the hydro sites are Francis type of turbine;
   
2. Generators which produces the electricity from the conversion of mechanical energy attributed to the turbine to electrical energy;
   
3. Hydraulic governor – controls the opening of the turbines wicket gates so that the desired RPM of the generator can be maintained;
   
4. Control panels – houses the metering and safety devices;
   
5. 5. Power transformer – steps up the generator voltage to 69 KV;
   
6. Miscellaneous electrical / mechanical equipment.