A Pelton wheel turbine is a tangent flow impulse turbine used to generate electricity in a hydroelectric plant. American engineer L.A. Pelton built the turbine.
The kinetic energy is the only energy that is accessible at the Pelton turbine inlet. Pressure atmospheric pressure at the inlet and outlet of the turbine. These turbines use for high heads.
Components of Pelton Turbine
Pelton turbines have different components that are given below:
Nozzle and Spear
Nozzles are used to increase the kinetic energy of water hitting buckets or vans connected to the runner.
The amount of water hitting the buckets is controlled by the spear. A spear is installed inside the nozzle and controls the flow of water that will attack the runner van. The spear nozzle is shown in the image below. It can be driven by the handwheel or automatically in the axial direction. The water flow rate increases when the spear is moved backward, and the water flow rate decreases when pushed forward.
Impeller and Buckets
The impeller is a moving component of the turbine. It is a circular disc on edge, where several buckets are placed at the same distance.
Buckets are made by joining in two semicircular bowls. Each bucket has a wall between two semicircular bowls called a splitter. The splitter splits the jet of water into two equal portions, and the spray of water comes out on the external edge of the blade.
The buckets are designed so that the water flow buckets with a deflection from 160 degrees to 170 degrees. Pelton turbine buckets are made of cast iron, cast steel, bronze or stainless steel.
The housing of this turbine is called the casing. The Pelton turbine with the casing is shown in the above figure.
This process prevents water splashing and helps to release water in trail races. It also acts as a shield in the event of an accident. Cast iron or prefabricated steel casing uses to cover the Pelton turbine.
When the water flow is completely stopped by pushing the spear forward, the amount of water hitting the runner becomes zero. But still, the runner continues due to the inertia of the runner.
A thin nozzle is needed, which guides the water jet to the rear of the van to stop the impeller quickly. This jet of water used to control the runner of a turbine is called a breaking jet.
How does a Pelton Wheel Turbine Work?
The operation of the Pelton turbine is effortless. In this type of turbine, high-speed jets emit water from the nozzles around the turbine. These tubes arrange so that the water jet collides with the bucket when it splits, with the water flow in the middle of the bucket dividing it into two streams. Two different streams then flow along the inner bend of the bucket and pour in the opposite direction from where the water comes. This change in water speed produces excitation on the blade of the turbine. This process produces torque and rotation on the turbine.
High-speed water jets are created by pushing high-pressure water (such as water falling from a high head) through a nozzle at atmospheric pressure. The maximum output can obtain from the Pelton wheel turbine when the excitation received by the blade is at a full, i.e., the water flow is precisely opposite to the direction in which the ides are facing the bucket. Also, these turbines have higher efficiency as the blade’s speed is half than the water jet speed.
Advantages of Pelton Wheel Turbine:
- Pelton turbine has the highest efficiency than hydro turbines.
- It works with a very flat efficiency curve.
- Each bucket separates the water jet in half, thereby balancing the side-load forces or pressing on the wheel and thus the bearings.
- It works at the high head and low discharge.
- It has a tangent flow, i.e., it has a radial flow or axial flow.
- These turbines have an easy assembly.
- It has fewer parts than the Francis turbine, which includes both stationary vans and guided vans.
- The overall capacity of the Pelton turbine is high.
- In the Pelton wheel turbines, both the first law of motion and the second law apply.
- The main benefit of the Pelton wheel turbine is that it hits the water jet on the turbine and goes to the runner at total atmospheric pressure.
Disadvantages of the Pelton wheel:
- With time, the capacity decreases very quickly.
- It has a large size of powerhouse, generators, and impeller.
- The alteration in the working head is hard to control due to the high discharge.