In a Pelton wheel turbine, the pressure energy of water is transformed into kinetic energy in the form of a high-velocity water jet, which then impacts the wheel in a tangential direction, causing it to revolve.
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What is a Pelton wheel turbine?
Lester Allan Pelton, an American engineer, was the inventor of the Pelton wheel turbine, which is a kind of impulse turbine used for high heads of water (more than 300 metre). Pelton wheel turbines are often deployed in areas with limited space.
It is a kind of hydraulic turbine used primarily in hydroelectric power plants. About 20% of the world’s energy is generated by hydroelectric power plants. Hydropower is the most widely used renewable energy source. It’s a cheap and reliable way to power homes and businesses.
Learn about: Francis turbine: Components,principle,advantages & disadvantages
Pelton wheel turbine: Design
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The construction of a Pelton turbine is not too complicated. A substantial disc in the shape of a circle is placed on a rotor, which is a revolving shaft of some kind. Buckets, also known as cup-shaped blades, are mounted on this circular disc, and they are uniformly placed across the whole wheel. In most cases, the buckets are positioned around the rim of the container in pairs.
The wheel is then fitted with nozzles, which are responsible for feeding water into the turbine and completing the process. These nozzles produce water jets that are directed at an angle perpendicular to the wheel of the turbine. The force exerted by the water jets against the buckets creates this, which in turn causes the turbine to spin as a consequence.
Also know: What is the physical significance of moment of inertia?
Pelton wheel turbine: Operation
The functioning of a Pelton turbine is simple. The nozzles surrounding this sort of turbine are used to create high-pressure streams of water that are shot out at fast speeds. These nozzles have been set in such a way that the water jet will strike the buckets at splitters, which is the middle of the bucket and the point at which the water jet is divided into two streams.
After that, the two distinct streams continue to flow down the inner curve of the bucket until exiting in the opposite direction that they entered. This alteration in the water’s momentum results in an impetus being applied to the blades of the turbine, which in turn generates torque and spinning inside the turbine.
The high-velocity water jets are produced by forcing water at high pressure, such as that which is dropping from high heads, through nozzles that operate at normal air pressure. When the impulse produced by the blades of a Pelton turbine is at its highest, the output from the turbine is at its highest as well.
This occurs when the water stream is deflected in a direction that is precisely opposite to the direction in which it hits the buckets. In addition, the efficiency of these wheels is at its peak performance when the speed of movement of the cups is equal to just one-half the speed of the water jet.
Pelton wheel turbine: Components
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Several components go into making up a single Pelton wheel turbine. Four of the most important components are as follows:
Nozzle
The nozzle is used to improve the kinetic energy of the water that will impact the buckets or vanes linked to the runner. The quantity of water reaching the runner’s buckets is regulated by putting a spear in the nozzle.
Regarding the dimension of the unit, the speed is shown by a conical needle and may be altered either mechanically or manually through a wheel located in the axial direction. The amount of water that hits the runner is reduced whenever the spear is moved closer to the nozzle in its forward position. Conversely, if the sphere is pushed back, the quantity of water hitting the runner increases.
Runner and buckets
The runner or blade of a Pelton wheel turbine is a circular disc on the perimeter of which numerous buckets are placed in an even alignment. This disc is the centre of the turbine. The bucket is shaped like a double hemispherical cup or bowl, and it has a separating wall in the middle that’s called a splitter. These two halves are identical to each other.
The jet of water strikes the splitter and is separated into two equal halves. The jets are discharged at the very edge of the bucket’s exterior. The bucket is shaped in such a way that the jet will be diverted via an angle of either 160 or 170 degrees. Depending on the pressure that is present at the intake of the turbine, the bucket may be manufactured out of bronze, cast steel, cast iron, or stainless steel.
Casing
The exterior covering of the Pelton turbine is referred to as the casing, and it may be composed of cast iron or steel plates that have been formed. It prevents the water from splashing about and contributes to the process of getting the water to the trail race. Additionally, it serves as protection if an accident does take place.
Breaking jet
When the water jet is completely shut off by moving the spear in the forward direction, there will be no more water hitting the runner, and this will result in the volume of water to zero. Despite this, the runner continues to run owing to the inertia that the runner has.
A diminutive nozzle is supplied, which directs the water jet towards the rear of the vanes to impede the runner in the least amount of time that is reasonably possible. The term “breaking jet” refers to the stream of water that is sent in the direction of the runner of the turbine to stop it.
Pelton wheel turbine: Applications
The following are some of the applications that may be made use of the Pelton wheel turbine:
- When the available water source has a relatively high hydraulic head but low flow rates, the Pelton wheel is the turbine of choice for hydropower generation because of its efficiency. In hydroelectric power plants, the head may range anywhere from 150 to 2,000 metre in height.
- High velocity generation of fluid: Using the Pelton Wheel Turbine one can achieve high fluid velocity for enhanced power and efficiency.
- This is used to drive generators that are attached to the turbine shaft. Using this, the mechanical energy from the turbine is converted into electrical energy for power generation.
Pelton wheel turbine: Advantages
The following is a list of many advantages that the Pelton wheel turbine offers:
- The Pelton wheel turbine is currently the most efficient kind of hydro turbine that one can purchase.
- It has a performance curve that is almost perfectly flat.
- It functions well even with a low discharge and a high head.
- Compared to Francis’s turbine, which features both guided and fixed vanes, this one has fewer moving parts and components.
- It is possible for there to be either axial flow or radial flow.
- The Pelton wheel turbine is not difficult to put together.
- Cavitation won’t happen in the Pelton wheel since the water jet only hits a particular portion of the runner.
- The total efficiency of the Pelton wheel turbine is quite high.
- In this particular form of the turbine, the first law of motion and the second law of motion are both put to use.
- This particular turbine operates at atmospheric pressure throughout the whole of the water jet, striking and exiting the runner, which is its primary benefit.
Pelton wheel turbine: Disadvantages
The following is a list of some of the drawbacks associated with the Pelton wheel turbine:
- The effectiveness rapidly declines over time.
- Within this turbine, the runner, powerhouse, and generator are all rather substantial.
- Because of the high heads, there are significant difficulties involved in maintaining control of the working head.
FAQs
When is a Pelton turbine the best option, and under what conditions?
Pelton turbines and wheels are excellent for use in power generation when the water energy to be extracted is available at a high head but with a low flow rate.
In a hydroelectric power plant, how does a Pelton wheel function?
Since the Pelton turbine is an axial flow turbine, water travels down the blade from the reservoir to the penstock, and then onto the nozzle at its lower end. The runner's blade causes it to revolve while the nozzle increases the jet's velocity.
How much power can a Pelton wheel generate?
Using the optimal specifications of a 4.6 m water head and 9 mm nozzle diameter, the highest amount of electrical power produced is 16.89 watts. To turn the Pelton turbine, a greater flow rate is required, and a bigger nozzle diameter achieves this.
What is the ratio of speed for a Pelton turbine?
It is the ratio of the peripheral velocity to the intake energy head.
What is the ratio of flow via a Pelton turbine?
It is the ratio between the flow velocity at the intake and the energy head at the inlet.
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