Impulse Turbine

IMPULSE TURBINE

Principle

If, at the inlet of the turbine, energy available is only kinetic energy, the turbine is known as Impulse Turbine. In the impulse turbine, all the potential (pressure) energy of water is converted into kinetic (velocity) energy in the nozzle before striking the turbine wheel buckets. Hence, an impulse turbine requires high head and low discharge at the inlet. The water as it flows over the turbine blades will be at atmospheric pressure. The impulse turbine may be radial flow or axial flow or tangential flow type.

1. PELTON WHEEL

The Pelton Wheel is a tangential flow impulse turbine. It is named after L.A. Pelton, an American Engineer, who developed the first impulse turbine in the year 1882. See Fig. 1.

Description

The main parts of the Pelton Wheel are as follows:

1. Nozzle and Spear: The amount of water striking the buckets of the Pelton wheel is controlled by a spear in the nozzle. Spear is a conical needle operated by a hand wheel.

2. Pelton Wheel with Buckets: Pelton wheel is a circular wheel. On the periphery of the wheel, a number of buckets are fixed. The shape of the buckets is a semi-ellipsoidal cup.

3. Casing: The function of the casing is to prevent the splashing of water and to discharge the water to tail race.

Working

Water at high pressure from the penstock pipe enters the nozzle provided with a spear. The pressure energy of water is converted into velocity energy, as it flows through the nozzle. By rotating the hand wheel, the spear is moved to control the quantity of water flowing out of the nozzle. When the spear is pushed forward into the nozzle, the amount of water striking the buckets is reduced.

The jet of water at high velocity from the nozzle strikes the buckets at the center of the cup. The impulsive force of the jet striking on the buckets causes the rotation of the wheel in the direction of the striking jet. Thus, the pressure energy of the water is converted into mechanical energy. The pressure inside the casing is atmospheric.

The Pelton Wheel operates under a high head of water. Therefore, it requires less quantity of water. Draft tubes are not usually used with it.