Pelton Turbine - Parts, Construction And Working

• Turbines:-

                The turbine is defined as the hydraulic machine which converts hydraulic energy into mechanical energy. This mechanical energy is used in running an electric generator which is directly coupled to the shaft of the turbine. Thus the mechanical energy is converted into electrical energy. The electric power which is obtained from hydraulic energy is known as hydroelectric power.

At present, the generation of hydroelectric power is the cheapest as compared to the power generated by other sources such as oil, coal, etc.

• Pelton wheel (Or turbine):-

           The Pelton wheel or Pelton turbine is a tangential flow impulse turbine. The water strikes the bucket along the tangent of the runner. The energy available at the inlet of the turbine is only kinetic energy. The pressure at the inlet and outlet of the turbine is atmospheric. This turbine is used for high heads.

     

                The water from the reservoir flows through the penstocks at the outlet of which a nozzle is fitted. The nozzle increases the kinetic energy of water following through the penstock. At the outlet of the nozzle, the water comes out in the form of a jet and strikes the buckets (vanes) of the runner. The main parts of the Pelton turbine are:

Pelton wheel turbine

1. Nozzle and flow regulating arrangement (spear),
2. Runner and buckets,
3. Casing, and
4. Breaking jet.

• Nozzle and flow regulating arrangement:- 

               The amount of water striking the buckets (vanes) of the runners is controlled by providing a spear in the nozzle. The spear is a conical needle that is operated either by a hand wheel or automatically in an axial direction depending upon the size of the unit. When the spear is pushed 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 disc on the periphery of which a number of buckets evenly spaced are fixed. The shape of the buckets is of a double hemispherical cup or bowl. Each bucket is divided into two symmetrical parts by a dividing wall which is known as a splitter. The jet of water strikes on the splitter. The splitter divides it into two equal parts and the jet comes out at the outer edge of the bucket. The buckets are shaped in such a way that the jet gets deflected through 160 degrees or 170 degrees. The buckets are made of cast iron, cast steel, bronze, or stainless steel depending upon the head at the inlet of the turbine.

• Casing:-

          The function of the casing is to prevent the splashing of the water and to discharge water to the tailrace. It also acts as a safeguard against accidents. It is made of cast iron or fabricated steel plates. The casing of the Pelton wheel does not perform any hydraulic function.

• Breaking jet:-

          When the nozzle is completely closed by move the spear in the forward direction. the amount of water striking the runner reduces to zero. But the runner due to inertia 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 vanes. This jet of water is called a breaking jet.