Electrical

What is a Pelton wheel turbine and how can it be used to generate electrical power?

A Pelton wheel is used to generate power and this wheel would utilize the flowing water impulse to create the turbine movement. These wheels are mostly used to generate electricity in the hydroelectric power plant. The Pelton wheel turbine can be described as a wheel that has good velocity, low flow, and high head. These wheels can be used for many medium and high head sites and these wheels can be assembled quickly. This wheel is capable to create power at small flow rates. The construction of the Pelton wheel is not complicated when compared to other turbines. These wheels can be operated at the high head and also in low discharges.

What are the major components of a Pelton turbine?

  • Nozzle with flow regulating arrangements
  • Runner with buckets
  • Casing
  • Breaking jet

Nozzle

A large penstock is used to take water to the hydroelectric plant site, and there will be a nozzle at the end of it. The conversion of pressure energy into kinetic energy can be achieved by this. The liquid will flow very fast because of this and this liquid would make an impact on the vanes which are mounted on the runner and thus the turbine rotation would take place. There is a sphere in this and it would control the amount of water that reaches the vanes, the sphere would move backward and forward to control the amount of water.

Runner and buckets

The runner is the turbine rotor, it is in a circular shape and consists of a certain number of cup-shaped buckets. So as we can see in the below image the bucker is in the shape of cups and the buckets are divide by a barrier and it is called a splitter, so when the water comes in contact with the splitter then the splitter would separate it into two parts and this splitter water goes through both sides of the vane and thus the end thrust is reduced in the bearing and in the shaft.

Casing

This part is used to control or prevent the splashing of the water, the casing encloses the runner. The casing would also prevent accidents, basically, the casing is the outer-covering of the turbine. The casing could be made of cast iron or from fabricated steel plates.

Breaking jets

This is used to stop the runner within less time, so while the movement of the sphere is in a forward, direction the nozzle will be completely closed. So because of this the amount of water that reaches the runner will be none. The runner would revolve for a long time because of inertia. So in order to stop the runner, a small nozzle would direct the jet of water to the back of the vanes, and this water is called a breaking jet.

How does a Pelton wheel turbine work?

The above image shows the operation of the Pelton wheel, water from the reservoir would reach the turbine through the penstock. A penstock is a solid pipe which would take water from the reservoir and it would transfer the water to the turbine at high speed. So while the water reaches the turbine traveling from the reservoir to penstock and when it comes out through the nozzle then the energy will be kinetic and not potential. Because of this conversion of the energy the water from the nozzle will be in the form of a jet and then it would come in contact with the vanes of the turbine. The jet water would create a great impact on the turbine and this would cause the movement of the turbine. The turbine is mounted on a shaft and there will be mechanical energy in the shaft and the shaft will be coupled to a generator and it would convert the mechanical energy into electrical energy and thus electricity is produced. In order to create more power, we can use two Pelton wheels in a single shaft or two water times to a single Pelton wheel.

The variation in the water momentum would create an impulse on the Pelton wheel blades. The rotation of the Pelton turbine would take place due to the torque which is created by the impulse. So if the impulse is good then the output of the Pelton turbine will be good too. So in order to achieve this change in the momentum of the water stream must be maximum. This can be achieved by diverting the water stream to the opposite direction which strikes the vanes.

What is the need for governing mechanism in a Pelton wheel?

The turbine speed should be maintained constant and it should be maintained so that the generator which is coupled to the turbine shaft would run at a constant speed during the varying load conditions. If the turbine load decreases then the water supply should be cut off, and this will be done by closing the nozzle. The sudden closure of the nozzle can cause excessive water hammers. In order to avoid the water hammer, the nozzle will be closed slowly and some of the water that comes out of the nozzle will be deflected from the bucket in a movable steel plate and it is a deflector. There will be variations in the turbine speed if there is any change in the load and this turbine is linked to the generator. The generator load would change according to the power consumption. So if the load is high then the turbine speed will be very low. In order to keep constant speed in a turbine spread-head mechanism is used. The spread-head can vary the speed in the nozzle and the spear rod movement is controlled by the governing mechanism.

The above image shows the governing mechanism of the Pelton wheel. So if the load falls then the turbine speed will be increased and this can be controlled by the governing mechanism. The flow to the turbine from the nozzle can be controlled by the governing mechanism.

What are the types of Pelton wheel turbines?

The Pelton wheel turbine is of two types and they are horizontal arrangement Pelton turbine and vertical arrangement Pelton turbine.

The horizontal arrangement Pelton wheel is used in medium and small-sized turbines and would mostly have one or two jets. The vertical Pelton has big wheels and it has many jets, these jets are distributed symmetrically around the turbine in order to balance the jet force.

What are the factors that must be considered while selecting a Pelton wheel?

  • Jet velocity
  • Wheel velocity
  • The deflection angle of the jet
  • Jet ratio
  • Diameter of the wheel
  • Bucket dimensions
  • Number of jets
  • Number of buckets

What are the advantages of the Pelton wheel turbine?

  • This wheel could provide axial flow or radial flow
  • It is not affected by variations in the flow
  • There won’t be any problem if it is not encased
  • It can provide good power even in low flow rates
  • Construction and assembly is really easy
  • Low cost
  • It operates with great efficiency
  • Maintenance is very less
  • These wheels are available in different sizes
  • There won’t be any atmospheric pollution

What are the disadvantages of the Pelton wheel turbine?

  • In order to produce power high-pressure head is required
  • Because of the long-distance, the penstock requirement is large
  • The water should be filtered so that blockage can be avoided
  • It would consume a lot of space and due to this the required powerhouse will be very large
  • Due to the high heads, the variations in the operating head will be very difficult to control

What are the applications of Pelton wheels?

  • They are suitable for semi-permanent applications 
  • These wheels are widely used for hydropower applications, it is suitable if the available water source has a good hydraulic head at low flow rates
  • Construction works
  • Mounting lodges
  • It can be used for seasonal business because they can be removed in case if they are no longer needed
  • This device is also used in drinking water supplies
  • The small Pelton wheels can be used to tap power from mountain streams

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