In the Pelton turbine water jets impacts on the blades of the turbine. The turbine is used to rotate the wheel to produce torque and power.
Design of Pelton wheel turbine
In the Pelton wheel to a rotor or rotating shaft circular disk is mounted. The circular disk consists of cup shaped blades. The cup blades are known as buckets. Those are placed at the circumference with equal spacing. To the wheel nozzles are arranged so the water jet ejects from the nozzle. The nozzles are tangential to the wheel circumference. No of nozzles depends upon the available water head and the operating requirement of the shape. The nozzles placed around the wheel are varying.Advertisement:
Parts of pelton wheel:
Penstock is a solid pipe structure and it is used to carry the water from dam to turbine at very high speeds.
In the penstock spear is provided and it is used to increase and decrease the speed of water which was entering in to the turbine. By moving the spear back and forward the water enter into the turbine by moving forward excess water is entering to the turbine.
Nozzle is attached to the end of the penstock. Main purpose of the penstock is used to increase the velocity of the water. The height velocity the water hits the buckets of the turbine.Advertisement:
To the runner a specified No. of wheels are attached. With the impact given by the buckets the runner starts rotating in the pelton wheel.
Runner is a large circular disc, where to that disc buckets are arranged. Then next runner is attached to the shaft.
To stop the turbine, water flow must be send back of the buckets by using another nozzle which is known as brake nozzle.
Working of pelton wheel turbine:
In the pelton wheel turbine the water from the nozzle straightly strikes the buckets arranged to the circumference of the wheel. In the middle of the bucket we can see the splitters. The water jets are divided into two equal watercourses. The watercourses are also known as streams. The water flows along with the internal curve of the bucket. The water leaves from the opposite direction of the incoming jet. With the help of the high speed water turbine the pelton wheel must be worked. The pelton wheels are expanding with the help of high pressure water through the nozzle to the atmospheric pressure. It receives the high pressure water jet from the water body which was situated at the high level to flow the water downwards.
Due to change in the momentum the stream water produces the impulse on the blade edges of the pelton wheel turbine. With the help of the impulse it generates the rotation and torque in the shaft of the pelton wheel. From the pelton wheel to attain the optimum output then the impulsive must be move backwards by the blades must be extreme. Maximum water stream is possible by change in the momentum. So it is found as soon as the water stream is bounced in the opposite direction to which it strikes the buckets with similar speed relative to the buckets.
Hydroelectric setup of pelton turbine:
By using the pelton turbine setup electricity is generated with the help of the water reservoir. The water reservoir must be situated at the height from the pelton wheel. Pressure channel is arranged and the water flows through the pressure channel to the penstock head. From the penstock head or with the help of supply pipeline the water passes through the nozzles. In that nozzles water flows with high speed and comes out as a high jet and it strikes the blades hardly. The pressure fluctuations are absorb and disperses with the help of surge tank.
By changing loads and speeds of the turbine constant water flow rate from the nozzle is possible. To obtain quality power output, constant speed is maintained in the turbine. To maintain constant speed instead of changing turbine water flow change through the flow of nozzles is changed. In the jet servo controlled spear valves are used to control the change of jet load to a change in the flow rate. Due to sudden reduction in the load the jets are repelled by using the deflector plate. Due to that the jets does not strikes the blades. Over fast-moving of the turbine must be prevented.
Hydraulic efficiency is defined as the ration of power developed by the runner to the power supplied at the inlet of the turbine
Mechanical efficiency is defined as the ratio of the power available at the turbine shafts to the available power at the turbine runner.
Volumetric efficiency is defined as the ratio of the volume of the water strikes the runner to the total water supplied by the jet to the turbine.
Overall efficiency is defined as the ratio of the power available at the shaft of the turbine to power available from the jet.