Hydro-Electric Power Plants: Classification, Components, and Operation

Hydro-Electric Power Plant

Classification of Hydro-Electric Power Plants

According to the Availability of Head:

1. Low head plants - head below 30 m
2. Medium head plants - head between 30 m to 180 m
3. High head plants - head 180 m and above.

According to the Nature of Load:

1. Base load plant
2. Peak load plant.

According to the Quantity of Water Available:

1. Run-off river plant without pondage.
2. Storage reservoir plant
3. Pump storage plant.

Such a plant has a large storage capacity of water; therefore, water collected in the rainy season is utilized during the dry period of the year.

The collection of water is done on a yearly basis; therefore, the capacity of the reservoir required is extremely large compared with the other types of hydroelectric power plants.

Elements of a Hydroelectric Power Plant

Reservoir:

To store water during the rainy season and supply the same during the dry season.

Trash Rack:

Its function is to prevent the entry of debris into the penstock, which may damage the wicket gates and turbine runner or choke up the nozzles of the impulse turbine.

Penstock:

It is a pipe from the reservoir to the surge tank. The penstock has to bear heavy pressure from inside during decreased load conditions of the generator and on the outside surface during increased load conditions of the generator. Therefore, it is constructed in heavy reinforced concrete or MS plates.

Surge Tank:

There is a sudden increase of pressure in the penstock due to a sudden decrease in the rate of flow of water to the turbine when the gate admitting water to the turbine is suddenly closed. This sudden rise of pressure in the penstock above normal pressure due to reduced load on the generator is known as "water hammer". To avoid water hammering and vacuum-forming tendencies, a surge tank is introduced near the powerhouse.

Power House:

It is a superstructure to protect the equipment. If a conventional topographic area is not available, one can prefer an underground powerhouse.

Prime Movers:

The main purpose of prime movers is to convert the kinetic energy (KE) of water into mechanical energy to generate electric power, for example, Pelton wheel, Kaplan turbine, Francis turbine, etc.

Draft Tube:

The draft tube is an essential part of the reaction turbine. It has a diverging shape. It is so shaped to decelerate the flow with a minimum loss so that the remaining kinetic energy of water coming out is recovered.