In this article, we shall see the working, parts, efficiency, advantages, disadvantages, and applications of the Pelton wheel turbine. We have also provided a PDF for the same.
The Pelton wheel turbine is a tangential flow impulse turbine used for high heads of water 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.
Introduction
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 which are as follows
- Nozzle
- Runner and buckets
- Casing
- Breaking jet
Nozzle
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 that 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 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 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
Casing
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 turbine does not perform any hydraulic function.
Breaking jet
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 to the back of the vanes. This jet of water is called a breaking jet.
Working Principle of Pelton Wheel Turbine
Let’s understand 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 a jet.
Now, the jet of water from the nozzle strikes the buckets (vanes) of the runner. So that the runner rotates at a 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 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.
Hydraulic Efficiency
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:
Mechanical Efficiency
It is defined as the power available at the shaft to the power produced by the runner.
Volumetric Efficiency
It is the ratio of the actual quantity of striking water 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.
Where Q= Water that struck on the runner & Delta Q= Amount of water discharged after striking.
Overall 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 turbine (Where ns=Specific Speed)
Calculation of Torque on the Runner
The formula of Flow Ratio: It is the ratio of the Velocity of flow of at inlet to the energy head at the inlet
The Formula of Speed Ratio: It is the ratio of Peripheral velocity to the energy head at the inlet
The Formula of Peripheral velocity: In the case of Pelton Wheel, the velocity at the inlet (U1) is equal to the velocity of the outlet (U2)
Calculation of Power
Advantages of Pelton Wheel
- The Pelton turbine is the most efficient of Hydraulic 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.
- The Pelton wheel turbine is very easy to assemble.
- There is no cavitation because the water jet strikes only a specific portion of the runner.
- It has fewer parts as compared to Francis turbine which has both fixed vanes and guided vanes.
- The overall efficiency of the Pelton turbine is high.
- For Pelton wheel turbines, both the first law and the second law of motion are applied.
- The main advantages are that In this turbine, the whole process of the water jet striking and leaving for the runner takes place at atmospheric pressure.
Disadvantages of Pelton Wheel
- The efficiency decreases very quickly with time.
- The Turbine size runner, generator, and powerhouse required are 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.
pelton wheel turbine working video
FAQ
Where Are Pelton Wheels Used?
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 other applications include the following
- Hydropower generation in mountainous regions with high-head water sources
- Remote power generation in off-grid or isolated areas
- Micro hydropower systems for small-scale applications
- Water treatment plants for mechanical power needs
- Experimental and research applications in fluid dynamics and turbine efficiency studies
What Is The Speed Ratio Of A Pelton Turbine?
It is the ratio of Peripheral velocity to the energy head at the inlet. The speed ratio of a Pelton turbine is the ratio between the tangential speed of the rotating buckets or blades and the speed of the incoming water jet. It typically ranges from 0.4 to 0.6, depending on the turbine design and operating conditions.
What Is The Flow Ratio Of A Pelton Turbine?
It is the ratio of the Velocity of flow at the inlet to the energy head. The flow ratio of a Pelton turbine compares the actual water flow rate to the design or rated flow rate. It indicates whether the turbine is operating at its intended capacity. A flow ratio of 1.0 means it matches the design flow rate, while values above or below indicate higher or lower flow rates, respectively. Monitoring and maintaining the flow ratio is crucial for optimal turbine performance.
Conclusion
In conclusion, the Pelton Wheel Turbine is an efficient and reliable type of hydropower turbine that utilizes the power of water to generate electricity. Understanding the different parts, working principles, advantages, disadvantages, and applications of this turbine is essential for anyone involved in the hydropower industry. By leveraging the strengths and weaknesses of this turbine, engineers, and designers can create effective and sustainable power generation systems.
References
more resources
Is a surge tank ever needed for a Pelton turbine?
No, surge tanks are not typically needed for Pelton turbines. Pelton turbines, designed for high-head, low-flow conditions, are less susceptible to water hammer effects, eliminating the necessity for surge tanks.