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How Does a Pelton Turbine Works ?



Due to its simplicity the Pelton Turbines is the most widely used turbine in the world .These are Invented by Pelton in 1890. Pelton Turbine is a Tangential flow impulse turbine in which the pressure energy of water is converted into kinetic energy to form high speed water jet and this jet strikes the wheel tangentially to make it rotate.

The largest units can be up to 200 Megawatts.Pelton turbines are best suited for high head and low flow sites.Depending on water flow and design, Pelton wheels can operate with heads as small as 15 meters and as high as 1800 meters.As the height of fall increases, less volume of water can generate same power.

In order to understand the working process of a  Pelton turbine you need to have knowledge about what are hydraulic turbines and also how they are classified :-


What are Hydraulic Turbine  ?
Turbine is hydraulic machine which convert hydraulic energy into mechanical energy. This energy is used in running an electric generator which is directly coupled to the shaft of the turbine. Thus we can say that the mechanical energy is converted to electrical energy. The turbines are classified according to the type of energy at inlet as 

1) Impulse turbine :- If at the inlet of the turbine the energy available is only kinetic energy the turbine is known as impulse turbine.
2) Reaction turbine :- If at the rate of a turbine the water process is kinetic energy as well as pressure energy the turbine is known as reaction turbine.

Also according to the direction of flow through runner: -
  1. Tangential flow turbine: water flows along the tangent of the runner
  2. Radial flow turbine : water flows in the radial direction through the Runner
  3. Axial flow turbine
  4. Mixed flow turbine.

Before we discuses how does the Pelton Turbine Works first let know about the  main parts of pelton turbine :-

Nozzle and spear arrangement :- 

The amount of water striking the buckets of the runner is controlled by providing a spear in the nozzle. The Spears is a conical needle which is operated either by hand wheel or automatically in the actual direction depending upon the size of the unit. When the spear is post forward into the nozzle the amount of water striking the runner is reduced on the other hand if the spear is pushed back the amount of water striking the runner increases



Runner and Buckets:- 
It consists of a circular track on the Periphery of which a number of buckets evenly spaced a fixed. the shape of the buckets is of a double hemispherical cup or bowl. Each is divided into 2 symmetrical parts by dividing wall which is known as splitter. HD vides the jet into 2 equal parts and the jet comes out at the outer edge of the bucket.

Casing :-
It prevents splashing of water and to discharge water to taol race. It also acts as a safeguard against accidents. It does not perform any hydraulic function.

Breaking Jet :- 
when the water striking the runner reduces to zero due to inertia, it goes on revolving for a long time, to stop the runner in a short time a small nozzle is provided which directs the jet of water on the back of the veins is jet of water is called breaking jet.

Working Process of Pelton Turbine  :-
  1. The water stored at high head is made to flow through a long conduit called penstock and reaches the nozzle of the Pelton turbine.
  2. Nozzle arrangement at the end of penstock helps the water to accelerate and it flows out as a high speed jet with high velocity and discharge at atmospheric pressure.
  3. The jet of water from the nozzle strikes the buckets (vanes) of the runner. This made the runner to rotate at very high speed.
  4. The quantity of water striking the vanes or buckets is controlled by the spear present inside the nozzle.
  5. The generator is attached to the shaft of the runner which converts the mechanical energy ( i.e. rotational energy) of the runner into electrical energy.
Basically Pelton Turbine classified into 2types according to their  are Arrangements as follows :-
  • Horizontal Arrangement of a Pelton Turbine.
  • Vertical Arrangement of a Pelton Turbine.
Horizontal Arrangement of a Pelton Turbine :-
Horizontal arrangement is found only in medium and small sized turbines with usually one or two jets. In some designs, up to four jets have been used. The flow passes through the inlet bend to the nozzle outlet, where it flows out as a compact through atmospheric air on to the wheel buckets. From the outlet the buckets the water falls through the pit down into the tail water canal.


Vertical Arrangement of a Pelton Turbine :-
Large Pelton turbines with many jets are normally arranged with vertical shaft.The jets are symmetrically distributed around the runner to balance the jet forces.The figure shows the vertical and horizontal sections of the arrangement of a six jet vertical Pelton turbine.

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