The Pelton wheel turbine is a tangential flow impulse turbine used for high heads of water and It is invented by Lester Allan Pelton, an American Engineer.
The energy available at the inlet of the turbine is only kinetic energy. The pressure energy at the inlet and outlet of the turbine is atmospheric.
This is a hydraulic turbine and the main uses of these turbines are in the hydropower plant to generate electricity.
In 2012, hydroelectric power plants contributed about 16% of the total electricity generation in the world.
Hydroelectricity is the most widely used form of renewable energy. It is a flexible source of electricity and also the cost of electricity generation is relatively low.
Parts of a Pelton Wheel Turbine:
A Pelton wheel turbine consists of four-major parts and those are:
- Runner and buckets
- Casing and
- Breaking jet
The amount of water striking the buckets of the runner is controlled by providing a spear in the nozzle.
The speed is a conical needle which is operated either by a hand wheel or automatically in an axial direction depending upon the size of the unit.
When the spear is pushed forward into the nozzle and the amount of water striking the runner is reduced. On the other hand, if the sphere is pushed back, the amount of water striking the runner increases.
Runner and buckets:
The runner or blade consists of a circular disc on the Periphery of which several buckets evenly spaced are fixed. The Shape of the bucket is of a double hemispherical cup or bowl. Each bucket is divided into two symmetrical parts by a dividing wall which is known as a splitter.
The jet of water strikes on the splitter. The splitter divides the jet into two equal parts and the Jets come out at the outer edge of the bucket. The bucket is shaped in such a way that the jet gets deflected through 160 degrees or 170 degrees.
The bucket is made of cast iron, cast Steel bronze or stainless steel depending upon the head at the inlet of the turbine
The function of the casing is to prevent the splashing of the water and to discharge water to the tailrace. It also acts as a safe ground against accidents. It is made of cast iron or fabricated steel plates. The casing of the Pelton wheel does not perform any hydraulic function.
When the nozzle is completely closed by moving the spear in the forward direction, the amount of water striking the runner reduces to zero. But the runner due to inertia goes on revolving for a long time. To stop the runner in a short time, a small nozzle is provided which directs the jet of water on the back of the vanes. This jet of water is called breaking jet.
Working Principle of Pelton Wheel Turbine:
Let's understand by the figure or layout of the hydropower plant, The water is stored at the high head. From there it comes through the penstock and reaches the nozzle of the Pelton turbine. The nozzle increases the kinetic energy of the water and directs the water in the form of the jet.
Now, the jet of water from the nozzle strikes the buckets (vanes) of the runner. So that the runner rotates at very high speed and the quantity of water striking the vanes or buckets is controlled by the spear present inside the nozzle and then the main important process is the generator is attached to the shaft of the runner which converts the mechanical energy (rotational energy) of the runner into an electrical energy.
The Efficiency of the Impulse or Pelton wheel Turbine:
The term "efficiency" is defined as the ratio of work done to the energy supplied.
It is the ratio of power generated by the runner of the turbine to the water-energy supplied to the bucket of the runner.
The expression is also written as:
Here H is a Net head developed by the water at the inlet, and it can find out by this equation:
It is defined as the power available at the shaft to the power produced by the runner.
It is a ratio of the actual quantity of writing on the runner blades per second to the net quantity of water supplied by the jet to the turbine per second is known as volumetric efficiency.
It is defined as a ratio of the power available at the shaft to the net power available at the base of the nozzle.
Mathematical Formula of Pelton Wheel:
The formula of Calculating Specific Speed of a Pelton Wheel (Where ns=Specific Speed)
Calculation of Torque on the Runner:
The formula of Flow Ratio:
The Formula of Speed Ratio:
The formula of Peripheral velocity:
Calculation of Power:
Advantages of Pelton Wheel:
These are some advantages of Pelton Wheel Turbine:
- The Pelton turbine is the most efficient of hydro turbines.
- It operates with a very flat efficiency curve
- Each bucket splits the water jet in half, thus balancing the side-load forces or thrust on the wheel and thus the bearings.
- It operates on the high head and low discharge.
- It has a tangential flow which means that it can have either axial flow or radial flow.
- Pelton wheel turbine is very easy to assemble.
- There is no cavitation because water jet strikes only a specific portion of the runner.
- It has fewer parts as compared to Francis's turbine which has both fixed vanes and guided vanes.
- The overall efficiency of the Pelton turbine is high.
- Pelton wheel turbines, both first law and the second law of motion are applied.
- The main advantages are that In this turbine, the whole process of water jet striking and leaving for the runner takes place at atmospheric pressure.
Disadvantages of Pelton Wheel:
And these are some disadvantages of Pelton Wheel Turbine:
- The efficiency decrease very quickly with time.
- The Turbine size runner, generator and powerhouse required is large.
- The variation in the operating head is difficult to control because of high heads.
Application of Pelton Wheel:
Pelton wheel is the preferred turbine for hydropower when the available water source has a relatively high hydraulic head at low flow rates.
In a hydroelectric power plant, This is used to drive the generator of the turbine and that generator generates the mechanical energy of the turbine into electrical energy.
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Here are some more resouces for you:Overview of Turgo Turbine
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So this is the overview of the Pelton Wheel Turbine, I tried my best to describe the whole thing, I hope you got the concept of Pelton Wheel.
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