Plants Based on Quantity of Water Available

1. These type of hydro plants do not store water and use the water directly taken from the river.
2. Since there is no control on the availability of water from the river, the power output of such plants fluctuates widely, hence, the utility of these plants is very less compared to other plants.

1. The utility of run-off river plants is increased by constructing a pond behind the dam near the plant.
2. The pondage capacity is decided based on 24 hours basis in order to cater for fluctuating loads on the plant.
3. With large pondage, firm capacity of the plant can be increased by few months.
4. These plants can serve satisfactorily both as base load and peak load plant.
5. These types of plants are frequently constructed in Europe where rivers have more or less uniform distributed flow round the year.

Storage type plants :

1. Storage type plants are constructed if the rainfall occurs only for few months in a year and the remainder period are dry as in case of our country.
2. In such plants a large amount of water is stored in a reservoir behind a dam and it is made available to power plant with controls on required basis.
3. These plants can be used both as base load as well as peak load plants.

1. These type of plants are suitable as peak load plants at locations where there is a storage of water since these plants are designed such that it pumps back a portion of its water supply from tail race to head race during non-peak periods.
2. The arrangement for such plants is shown in Figure.
3. The power for running the pumps for pumping of water back is supplied with secondary power from other plants such as steam a nuclear plants or run-off river plants.
4. Such plants work in conjunction with steam power plants and it improve the overall thermal efficiency of the combined power plant since the efficiency of thermal power plants is poor at part loads.
5. Recently several successful pumped storage plants have been constructed with reversible pump turbines.
6. Such a unit acts as a turbine to develop power when rotating in one direction and the same unit acts as a pump when it rotates in reversed direction.
7. In these plants very little water is required for its operation compared to other types of hydro power plants since the additional water is only required to take care of seepage and evaporation from the storage reservoir.

Mini and micro hydel power plants :

1. In order to meet the present power crisis upto a certain extent, mini and micro hydel power plants can be built along a stream of river in our country.
2. Mini power plants work in the range of 5 to 20 m head while the micro hydel plants work under a head less than 5 m.
3. Such low head mini hydel plants in our country have not been explored except in the states of U.P., H.P. and Arunachal Pradesh since the capital cost per kW is high.
4. It is estimated that the potential of these mini plants scattered all over the country may be as much as 20000 kW.
5. These plants in small capacity can easily be constructed in a much shorter time compared to other hydro plants which requires few years for their construction.
6. Mini hydel plants use special type of turbine called bulb type turbines.
7. In these turbines the scroll casing has been modified in the form of horizontal tapering duct with the flow passage forming a sort of throat where the turbine runner is located.
8. The draft tube of the turbine is replaced by a straight diverging tube.
9. Such a system reduces the hydraulic losses.