Pelton Wheel or Pelton Turbine refers to the Tangential Flow Impulse Turbine. This Turbine is basically utilized for High Heads and it was named after its creator, L.A.Pelton. The water strikes the container alongside the curvature of the tangent of the runner. The energy obtainable at the inlet of the turbine is just Kinetic Energy. The pressure at the inlet and outlet is known as the atmospheric pressure. The nozzle augments the kinetic energy of the water which is passing through the penstock. At the opening of the nozzle, the water sips out in the form of a jet and forays the containers (vanes) of the runner. Pelton Wheel Turbine is normally utilized for High Heads. Pelton Wheel Turbine has a Specific Speed of maximum 30(S.I) for single jet and somewhere around 30 and 60 (S.I) for multi-jet.
The chief parts of Pelton Turbine are:
- Nozzle and Flow Regulating Arrangement
The volume of water striking the buckets is measured by giving a spear in the nozzle. The spear refers to the pointed needle functioned in the axial direction which is in turn based up on the volume of the unit. When the spear is projected onward, the volume of water striking the runner is diminished and when the spear is pressed back, the quantity of water striking the runner highly augments.
- Runner and Buckets
Runner comprises of a spherical disc on the margin of which a multiple number of buckets consistently spaced are joined. The distance of the buckets is of a twofold semicircular cup or bowl. Every one of the bucket is divided into multiple symmetrical segments by separating wall which is called Splitter. The Splitter separates the jet into two equivalent parts. The buckets are shaped in such a form that the jet gets bounced through 160° or 170°. The buckets are constructed out of cast iron, cast steel bronze or stainless steel based upon the head at the inlet of the turbine.
The purpose of water is to avert the splashing of water and to liquidate water to tail race. The casing of Pelton Wheel shall not execute any kind of Hydraulic function.
- Breaking Jet
At the point, where the nozzle is totally shut by shifting the spear in the onward direction, the quantity of water striking the runner lessens to nil. However, the runner because of inertia continues to revolve for a longer period of time. To halt the runner in a short time, a tiny nozzle is given which guides the jet of water on the back of vanes. This jet of water is basically known as Breaking Jet.
Points to remember for Peltron Turbine
(i) The velocity of the jet at inlet is given by
Where = co-efficient of velocity =0.98 or 0.99.
H= Net head on turbine
(ii) The velocity of when (u) is given by
Where = speed ratio. The value of speed ratio varies from 0.43 to 0.48
(iii) The angle of deflection of the jet through the buckets is taken at 165oif no angle of deflection is given.
(iv) The mean diameter or the pitch diameter D of the pelton turbine is given by
(v) Jet Ratio: it is known as the ratio of the pitch diameter (D) of the pelton turbine to the diameter of the jet (d). It is indicated by m and is expressed as
m = D/d (=12 for most cases)
(vi) Number of bucket on a runner is expressed by
Where, m= jet ratio
(vii) Number of jets: it is basically calculated by dividing total rate of flow through the turbine by the rate of flow of water through a single jet.