Hydro-Electric Power Plant

HYDRO-ELECTRIC POWER PLANT

The word "hydro" means water and "electric" means electricity. In hydro-electric power plant, the output is electrical power and input is hydraulic power. So, it may be defined as power plant which converts the hydraulic energy of the water in reservoir into electrical energy, intermediate is mechanical energy.

1. General Layout of Hydro-Electric Power Plant

Figure 5.1 Shows a general layout of a hydro-electric power plant with pelton wheel turbine & figure 5.2 shows a general layout of Hydroelectric power plant with reaction turbines. It has the following components, as follows

1. Dam:

A dam is constructed across a river with reservoir to store water. Dam is used to increase the height of water level and there by increasing the capacity of reservoir and also helps to increase the working head of the power plant. Top surface of water in the dam in called head race.

2. Penstock:

Penstock is a pipe, which carries water under pressure from the dam reservoir to the turbines.

3. Surge tank:

The surge tank is introduced between the dam and turbine. It is used to reduce (or) increase the water flow rate in the penstock according to the turbine load and demand. When water flow into the turbine is reduced suddenly due to decreased load demand; then the water level rises in the surge tank. When water flow into the turbine is increased suddenly due to increased load demand, then additional water is supplied by the surge tank.

4. Water turbine (or) hydraulic turbine:

Water from the penstock enters into the turbine through the inlet Gate valve. Water turbine converts converts kinetic energy of water into mechanical energy tooduce electrical energy. Turbines having different types of vanes (or) buckets fitted in the wheels (or) runner. The rotating elements of runner shaft is directly coupled with the generator shaft, so the mechanical energy further converted into electrical energy through generator. 

5. Draft tube and Tail race:

A draft tube and tail race are the channels to convey water from the turbines to the downstream channel (or) river.

2. Head & Efficiency of Turbine

1. Gross Head (Hg)

The difference between the head race level to rail race level, neglecting the loss of head due to friction is known as Gross head. It is denoted by (Hg)

2. Net head (or) Effective head (H)

The head available at the inlet of the turbine when water is flowing from head race to the turbine is known as Net head. It is the difference of Gross head to the frictional head. It is denoted by (H).

Net head (H) = Gross head (Hg) - Frictional head (hf)

3. Frictional loss of head (hf)

When the water flow in the penstock, there will be some reduction in the amount of head due to friction between the penstock surface to water. This loss of head is known as frictional loss of head. It is denoted by (hf).

4. Efficiency (η)

4. a) Hydraulic efficiency (ηh):

It is defined as the ratio of power delivered by the runner to the power available at inlet of turbine. Power at inlet of the turbine is more and it goes on decreasing as the water flow over the vanes of turbine because the vanes are not so smooth.

4. b) Mechanical efficiency (ηm):

It is defined as the ratio of power available at the turbine shaft to the power delivered by the runner. Due to the mechanical losses, the power available at the shaft of a turbine is less than the power developed by the runner.

4. c) Volumetric efficiency (ηv):

It is defined as the ratio of the volume of water actually stricking the runner to the volume of water supplied to the runner.

4. d) Overall efficiency (ηo):

It is defined as the ratio of power available at the turbine shaft to the power available at inlet of the turbine.