Pelton turbine || Pelton wheel turbine

Here we are going to discuss about Pelton turbine and Pelton wheel turbine. As we know that turbine is a electrical equipment which is used to convert kinetic energy into mechanical energy. Among them Pelton is the one of the most useful for high head and low discharge.

Pelton turbine or Pelton wheel turbine

It is an impulse type which is run by the impulse of water. It is one of the most efficient hydraulic turbine which is invented by Lester Allan Pelton (1829 - 1908) in 1870. When water is flow from the dam to the turbine through penstock (a pipeline which is used in hydropower plant to flow water from head race to tail race or power house section), the water will hit the blades or buckets by guide mechanism by the help of nozzle. This machine is working on the principle of Newton's second law. This is mostly used in the power plant where water head is medium to high and flow of water is low.

Working principle of Pelton wheel

In a Pelton wheel, there are a number of buckets or blades which will helps to rotate it by converting kinetic energy into rotational mechanical energy. At the end of penstock, there is nozzle which work is to increase the pressure of water. One side of nozzle has larger cross-sectional area whereas another side has smaller cross-sectional area. Due this this shape, water pressure is increased while flowing from nozzle but after coming out from the nozzle, water pressure will be same i.e. atmospheric pressure. 

For a single jet, there is a jet from where water will flow & hit the bucket and split in half so that each half is turned and deflected back almost through 180⁰.  Here, the water will hit straightly to the bucket/blades which is the main difference as compared to Turgo-turbine.

For a multi-jet, there are 2 or more than 2 jets from where water will flow and hit the bucket so that it will help to increase the speed of rotation as well as increase the efficiency of turbine of same size. It also help to control the flow rate and reduce surge pressure. But it makes more complexity in design, increase more frictional losses.

Components of Pelton Turbine

1. Runner :- The runner consists of a number of buckets (in even number) in the periphery of a circular disc with equal spacing.

2. Nozzle :- It is a small pipe which one end is connected to the penstock from that connection its diameter will be reduced as shown in figure. It consists of spare value for guiding of water flow so that water flow rate can be controlled easily as per requirement.

3. Casing :- The water which hits the bucket will be splashed and it should not go outside so that it will help to help to discharge the splashed water to tail race.

4. Shut off valves :- These valves are used to fully isolate the water from turbine where there is gate valve or butterfly valve. It will be fully open in turbine operation and closed while turbine is not operated. While this valve is closing, it is move slowly to reduce surge pressure so that it will prevent the bursting of penstock. But it is not used for flow regulation as spare valve.

5. Spare valve :- This valve is the most important valve in  continuous flow regulation which is placed inside the nozzle. It will operate automatically or manually to control flow but in general it is connected to governor for automatical operation for frequency control.

6. Deflector plate :- This is used to deflect the water from jet to the buckets so that turbine can be stopped without  shutting the flow of water in penstock. It is operated electromagnetically so that when it is magnetized, it will let the water to hit the turbine bucket and when it is demagnetized, it will not let the water to hit the turbine bucket.

There is an animation figure of Pelton wheel turbine.