Hydal / Hydro Power Plant

In hydro electric power plant the water under pressured is directed to the hydraulic turbine. The water under pressured is obtained from a natural water fall in the pressure is produced from storage of water in a reservoir. The potential energy / kinetic energy of water is converted into mechanical energy by turbine. This mechanical energy is then converted into electrical energy by electrical generator coupled to shaft of the turbine. The main object of the hydro power plant may be as follow.

  1. Flood controlled
  2. Storage of water for irrigation and electric power generation

Site Selection for Hydal Power Stations.

The suitable site for hydro electric power station is selected considering the following factors.

  1. The water must be available it in a use full head and in enough quantity.
  2. If the flow of water is not regular enough for continuous supply, there must be a convenient accommodation for the construction of a dam and making a reservoir at a reasonable cost.
  3. Catchment area must be the largest for storing water at a high head.
  4. The soil and rocks must be suitable for the construction of Dam, storage of water and the installation of bulky machinery.
  5. The constructional material, such as earth, gravels, rocks, concreate, aggregates should be available in the neighborhood area.
  6. The cost of land which will be some submerged under water should be reasonable.
  7. Transport facility should be available, and the site should be accessible easily.

Parts of Hydro Power Plant

A hydal power plant consist of the following main parts.

  1. Catchment area

    it is the area bounded by the water sheds and tributes, which drain into a river so that water flows fast a given point. Which is suitable for construction of a dam and power station.

  2. Dam – Reservoir

    Dam is civil structure which is constructed to create a hydraulic head. Water from the catchment area collects at the back of the dam to form a storage reservoir.

  3. Spill Ways

    All the dam are provided with spill ways to discharge excessive water in the reservoir beyond the full permissible level various type of spillways are used.

    1. Slide spill way

    2. Chute spill way

    3. Shaft spill way

    4. Syphon spill way

  4. Intake

    A structure constructed to divert the water from the reservoir in penstock to control condition.

  5. Fore bay

    It is the enlarge body of water just above the intake.

  6. Penstock (Pipe lines, Tunnels)

    The water is conveyed from the reservoir to the turbine in the power house by pipe lines or tunnels, which are known as penstock. Penstock may either be low pressure or high pressure. For low pressure penstock pipes are used. Steel pipes are used for high pressure penstock.

  7. Surge Tank

    It is a concrete tower of a high comparable with the operating head of water in the reservoir. It is connected to the penstock. Its purpose is to dissipate or reduce the pressure of water of the penstock by rising it in the tank in the event of sudden shutdown of turbine. This sudden change of pressure above the normal is known as water bammer surge. Tank is particularly necessary in high head installation

  8. Water or Hydraulic Turbine

    The kinetic and potential energy of water is converted into mechanical energy by hydraulic turbine. Turbine are divided into two main types.

    1. Impulse Turbine
      In the impulse turbine the wheel water acting on the wheel is supplied through the nozzle. In this turbine the potential energy of water is converted to kinetic energy before entering the wheel through the nozzle. The impulse turbine is generally a pelton wheel turbine. Pelton wheel is a special type of axical flow impulse turbine. The jet of water entered to the wheel from one or more nozzles and strikes the blades on the center and flows axially. The blades ae known as buckets and each bucket consist of double semi-spherical cups. Pelton wheel are also called velocity turbine.

    2. Reaction Turbine
      In reaction turbine the water passages or flow are completely filled with water. The water inters the wheel under pressure all around the wheel and flows over the vans. In passing over the vans the pressure head is converted to velocity head and the pressure is finally reduced to atmospheric pressure, after leaving the wheel.

  9. Electric Generator

    The electric generator is coupled to the hydraulic turbines. These generators convert the mechanical energy into electrical energy.

  10. Tail Race

    After driving the turbine the water leaves the power house and discharges into a tail race.

Classification of Hydro Power Station

The hydro electric power plant can be classified according to the following features.

  1. Quantity of water available
    1. Run off river plant without poundage
    2. Run off river plant with poundage
    3. Reservoir Plant
  2. Nature of load to be supplied
    1. Base load plant
    2. Peak load plant
  3. Water head available
    1. Low head
    2. Medium head
    3. High head
  1. Quantity of water available


    1. Run off river plant without poundage

      In this type the water is taken from the river directly and no poundage or storage is used. These plants can use water from the river as and when available. The frame capacity of such plant is low if the supply of water is not uniform throughout the air.

    2. Run off river plant with poundage

      In such plant’s poundage is designed. Poundage is the storage of water at the plant which make it possible to cover with hour to hour fluctuation of load throughout a week or some longer period depending on size of poundage. With enough poundage the frame capacity of such plant is increased. Such plants are more useful then without poundage plants.

    3. Reservoir Plant

      In such plant water is stored behind a dam which is available to the hydroelectric plant with control as required, such plant has better capacity and can be used throughout the air. Its frame capacity is increase and it can be used either as a base load plant or peak load plant as required. Most hydroelectric power plants are of this type.


  2. Types according to Nature of load


    1. Base load Plant

      These are hydro electric plant which can take up load on the base portion of the load curve. Load curve of the power system these plants have larger capacity. Base load plants will be kept running practically on block load (A load that is practically constant) the load factor of base load plant is high.

    2. Peak load

      Plants used to supply the peak load of the system corresponding to the load it the top portion of the load curve are known as peak load plant run off river plants with poundage can be used as peak load plant.

  3. Types According to available head

    hydraulic head is defined as the different between the level in the reservoir behind the dam and the water level in the river, where tail race is located. According to the available head the hydal power plants are classified into the following types.

    1. Low head

      These plants which have a head up to 70meters or below are group as low head plats. Vertical shaft Francis turbine used in such plant.

    2. Medium head

      The plants having a head of 70m to 300 meters are called medium head plants. For these plants modified form Francis turbine is used.

    3. High head

      The hydro power plants which are installed for a head of above 300 meters are called high head plants. For this head horizontal shaft polton wheel turbine are used


  1. Beside the generation of electric power these are also useful for flood control, storage of water for irrigation and drinking purposes.
  2. The operating cost and running cost / KWH for these power plants is less as compared to the other power plants.
  3. The involve a large amount of construction work opportunities are available for employment of man power of the society.


  1. A huge civil engineering works is necessary to store water and provide a considerable head (level), therefor the capital cost is larger for hydal power plant as compared to other types of plants.
  2. Hydal electric power plant are commonly mega projects and the dam and reservoir, sometime displaces populated area and covers irrigated area and this having negative environmental effects on the society.