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CONSTRUCTION OF PELTON TURBINE

CONSTRUCTION OF PELTON TURBINE 
Introduction
The Pelton wheel turbine is a pure impulse turbine in which a jet of fluid leaving the nozzle strikes the buckets fixed to the periphery of a rotating wheel. 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. The turbine is used for high heads ranging from (150-2000) m. The turbine is named after L. A. Pelton, an American engineer.

Parts of the Pelton turbine:-
Nozzle and flow control arrangement:
The water from the reservoir flows through the penstocks at the outlet of which a nozzle is fitted. The nozzle converts the total head at the inlet of the nozzle into kinetic energy. The amount of water striking the curved buckets of the runner is controlled by providing a spear in the nozzle. The spear is a conical needle which is operated either by a hand wheel or automatically in an axial direction depending upon the size of the unit.

 Picture - Pelton Turbine

Runner and buckets:
The rotating wheel or circular disc is called the runner. On the periphery of the runner 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 the splitter. The jet of water strikes on the splitter. The splitter then divides the jet into two equal parts and the water comes out at the outer edge of the bucket. The buckets deflect the jet through an angle between (160o-165o) in the same plane as the jet. Due to this deflection of the jet, the momentum of the fluid is changed reacting on the buckets. A bucket is therefore, pushed away by the jet.

Casing:
The casing prevents the plashing of the water and discharges the water to tail race. The spent waterfalls vertically into the lower reservoir or tail race and the whole energy transfer from the nozzle outlet to tail race take place at a constant pressure. The casing is made of cast iron or fabricated steel plates.

Breaking jet:
To stop the runner within a short time, a small nozzle is provided which directs the jet of water on to the back of the vanes. The jet of water is called the "breaking jet ". If there is no breaking jet, the runner due to inertia goes on revolving for a long time.

REFERRED BY :- ER. SUNIL KUMAR, A.P., MECHANICAL ENGG. DEPTT., SGI
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