Pelton Wheel

Pelton wheel [′pel·tən ‚wēl]

(mechanical engineering)

An impulse hydraulic turbine in which pressure of the water supply is converted into velocity by a few stationary nozzles, and the water jets then impinge on the buckets mounted on the rim of a wheel; usually limited to high head installations, exceeding 500 feet (150 meters). Also known as Pelton turbine.

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Pelton Wheel 

the most widely used type of hydraulic impulse turbine, using the kinetic energy of a stream of water. The design was patented by the American engineer A. Pelton in 1889.

The flow section of a Pelton wheel consists of a nozzle, a runner, and an offtake. The water travels from the penstock through the nozzles to the blades (buckets) of the runner along a tangent to a circle passing through the center of the bucket. Unlike reaction hydroturbines, a Pelton wheel does not require suction piping, and the water enters the buckets of the runner not continuously but rather only when the buckets pass through the zone of the pressure jet. By moving a needle located inside the nozzle, the cross section of the nozzle outlet can be adjusted; this in turn regulates the water flow. To avoid water hammer in the penstocks and runaway acceleration of the unit when the load is removed during operation, baffles (deflectors or splitters) can be incorporated in Pelton wheels. Such baffles compress either all or part of the flow toward the periphery of the runner, so that the stream misses the buckets. The number of buckets chosen is the minimum required to prevent the pressure jet from entering the space between buckets. Most Pelton wheels have 18–26 buckets; they are built with horizontal or vertical shafts. Horizontal turbines have one, two, or three runners on a shaft and one or two nozzles for each runner. Vertical turbines are manufactured with one runner and with several nozzles.

Pelton wheels are used for heads greater than 500–600 m. The highest head used in turbines now in operation is about 1,800 m (the Reiseck hydroelectric power plant in Austria). In the USSR, Pelton wheels with a rated power of 54.6 megawatts have been put into operation in the Tatev Hydroelectric power Plant (with a head of 569 m).

REFERENCE

Edel’, Iu. U. Kovshovye gidroturbiny. Moscow-Leningrad, 1963.

M. F. KRASIL’NIKOV