Impulse turbine: Working principle of Pelton Turbine
Impulse turbine and Working principle of Pelton Turbine:
I know you heard about generating electricity from hydropower plants, yes, this is done by turbines. The work produced by a turbine can be used for generating electrical power when combined with a generator.
A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work by a system of fixed and moving blades and causing the wheel to rotate.
Water turbine was developed in the 19th century and was widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy source.
You know what makes them so efficient that they are lightening up our houses. An efficient turbine can utilize up to 90% of the water’s potential energy.
Although there are various types of impulse turbines available, but Pelton wheel turbine is the most widely used impulse turbine. We can generate maximum up-to 200 MW of electricity from a Pelton wheel turbine, where we have water head (height of stored water), as high as one thousand meters.
So in this article, we’ll discuss impulse turbine and Pelton wheel.
1. Impulse Turbines:
Impulse turbine changes the velocity of a water jet. The jet impinges on the turbine’s curved blades which change the direction of the flow. The resulting changes in momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy.
prior to hitting the turbine blades, the water’s pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades, and the turbine doesn’t require hosing for operation.
Newton’s second law describes the transfer of energy for impulse turbines.
Impulse turbines are most often used in very high head applications.
2. Working of Pelton Turbine:
The Pelton-wheel is an impulsive turbine used for high heads of water. This turbine was discovered by the American engineer L.A. Pelton. The energy available at the inlet of the Pelton turbine is only kinetic energy. The pressure at the inlet and outlet of the turbine is atmospheric pressure. It has the following main components.
- Runner and buckets
- Breaking jet
- It is a circular guide mechanism, which guides the water to flow in a designed direction, and also to regulate the flow of water.
- This water, in the form of a jet, strikes the buckets. A conical needle or spear operates inside the nozzle in an axial direction.
- The main purpose of This spear is to control or regulate the quantity of water flowing through the nozzle as shown in Fig.
Runner And Buckets
- The runner of a Pelton wheel essentially consists of a circular disc fixed to a horizontal shaft, on the periphery of the runner; a number of buckets are fixed uniformly.
- The casing of a Pelton wheel does not perform any hydraulic function. but it is necessary to safeguard the runner against accident, and also to prevent the splashing of water and lead the water to the tailrace.
- The casing is, generally, made of cast or fabricated parts.
- Whenever the turbine has to be brought to rest, the nozzle is completely closed. it has been observed, that the runner goes a revolving for a considerable time, due to inertia, before it comes to rest.
- In order to bring the runner to rest in a short time, a small nozzle is provided in such a way, that direct a jet of water on the back of the buckets.
- It acts as a brake for reducing the speed of the runner.
3. Working of Impulse Turbine
The water flows along the tangent to the path of the runner. Nozzle direct forceful streams of water against a series of buckets mounted around the edge of a wheel. As water flows into the bucket, the direction of the water velocity changes to follow the contour of the bucket.
When the water-jet contacts the bucket, the water exerts pressure on the bucket and the water is decelerated as it does a “u-turn“ and flows out the other side of the bucket at low velocity. In the process, the water’s momentum is transferred to the turbine This “impulse “ does work on the turbine. For maximum power and efficiency, the turbine system is designed such that the water-jet velocity is twice the velocity of the bucket.
because water and most liquids are nearly incompressible, almost all of the available energy is extracted in the first stage of the hydraulic turbine. Therefore, the Pelton wheel has only one turbine stage, unlike gas turbines that operate with a compressible fluid.
4. Application Of Impulse Turbine
- Pelton wheels are the preferred turbine for hydro-power when the available water source has a relatively high hydraulic head at low flow rates.
5. Advantages and Disadvantages of Impulse Turbine
- Simple in construction and easy to maintain.
- This turbine has high efficiency.
- They work at atmospheric pressure so no problem of leakage.
- It is easy to assemble.
- This is not the best turbines for low-pressure streams by a high flow rate.
- Impulse turbines are large in size compare to others.
- Efficiency decreases with time.
- It is costly to install.
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