A turbine is a mechanical device that rotates and produces electricity. These turbines can be categorized according to their uses as either water turbines or hydro turbines, gas turbines, steam turbines, or wind turbines. They can be divided into two categories, such as impulse turbines and reaction turbines, based on how the force between the water and the turbine is transferred. These turbines are primarily used to convert the water supply’s potential and kinetic energy into mechanical work. The workings and applications of an impulse turbine, one of the hydro turbine types, are covered in this article.

What is Impulse Turbine?

In an impulse turbine, the rotor and colloids are driven directly through the rotor blades by a water jet from the penstock, making it the most widely used type of turbine. As the name implies, this turbine operates using the impulse force generated when the water jet’s blade is struck. Major parts of this turbine include a set of blades and nozzles. The diagram of an impulse turbine is displayed below.

This turbine has a number of stationary nozzles that convert the pressure of the jet water into kinetic energy. When the water has passed through the nozzle and reaches the impeller blades, the kinetic energy of the jet water is captured, turning it into water speed. These turbines are therefore used for high head functions and low water flow rates. The main distinction between an impulse turbine and a reaction turbine is that in an impulse turbine, all of the water’s hydraulic power can be converted into kinetic energy using nozzles, and there are no force changes during the process, whereas in a reaction turbine, only a portion of the energy that is readily available is converted into kinetic energy.

Impulse Turbine Construction

Different parts can be used in the construction of an impulse turbine. Therefore, the main elements of an impulse turbine are;

Penstock

Water is delivered to the impulse turbine through a pipe or channel called the penstock of this turbine. Due to the placement of the turbine at the bottom and the reservoir at the top, this penstock is very useful in transferring water from the reservoir to the turbine.

Nozzle

The nozzle’s primary job is to supply the impeller blades with water. Here, water is supplied through a nozzle from the reservoir so that the potential energy of the water pressure can be converted into kinetic energy. Once this conversion is complete, the impeller blades where the water strikes them receive enhanced water kinetic energy.

Runner/Impeller

The turbine’s runner has the form of a circular disk that is mounted on a rotating shaft known as a rotor. The runner is evenly curved, and the cup-shaped blades (buckets) are arranged on it as well.

Bucket

A wind turbine’s buckets are spoon- or cup-shaped blades that are roughly positioned at the edge of the runner to allow energy transfer between the turbine and water. These buckets are constructed from cast iron or stainless steel. When the water jet leaves the nozzle, it hits the buckets in the turbine, turning it and removing the external bucket edge. In comparison to the impact angle, the fluid direction will change during the exit depending on the turbine design. This angle needs to be 180⁰ degrees to acquire a lot of energy. However, in this case, the angle is limited to 170⁰ because the exit flow from one bucket does not slam into or break the next bucket.

Casing

Cast iron serves as a shield of protection for the turbine. This shield directs the spillway channel to prevent water from dispersing while providing protection from water splatter. All of the turbine’s parts are shielded from the outside environment by this shield.

Braking Jet

After the water flow is stopped from the nozzle, the brake jets are crucial for avoiding the turbine blades. Even after the water supply has been shut off, the turbine’s blades will continue to turn. In order to prevent the turbine blade from turning instantly, it will hit from the opposite side of the blade.

Spear

The spear’s structure is conical and attached to the nozzle to control the flow of water into and out of the nozzle and strike the bucket.

Impulse Turbine Working

Newton’s second law of motion serves as the foundation for how the impulse turbine operates. For these kinds of turbines, the water can be kept in high-altitude reservoirs and delivered via penstock to the turbine, which is situated on the ground. The process that this turbine uses is as follows.

• A water jet moves from a dam or reservoir to the connected nozzles in the turbine.
• When water is injected into the turbine’s nozzle, it converts the pressure water’s potential energy into kinetic energy.
• The water jet strikes the impeller blades after exiting the nozzle and rotates the impeller around its axis.
• These blades primarily convert the water jet’s kinetic energy (K.E.) into speed and increase the water speed.
• The water with high speed hits the turbine so that shaft of the turbine starts turning.
• The generator coil is connected to the turbine shaft, and the shaft’s rotation causes the generator coil to also rotate.
• When the generator coil begins to rotate, electricity is produced and delivered to various homes and businesses.

Impulse Turbine Types

Impulse turbines are available in three types like Pelton, turgo, and crossflow.

Pelton Turbine

The most popular kind of impulse turbine is this one. Each bucket in this type of turbine has two cups with splitters sandwiched in between the double cups. To improve the performance of the turbine, this device divides the water jet between the two cups. In contrast to micro-level hydroelectric plants, where efficiency can reach up to 90%, Pelton turbines have a maximum efficiency of 95%.
The following are the main characteristics of the Pelton turbine.

• The water discharge capacity of these turbines ranges from 5 liters to 1000 liters per second
• As opposed to reaction turbines, installation of these turbines is simpler because they have low flow rates and use small pipes.
• These turbines function despite the high-water head because a complex and expensive Penstock is needed.

Turgo Turbine

The Turgo turbine can operate at medium heads. The buckets in this turbine include single, thinner cups. The water jet in this turbine exclusively strikes the bucket at a 20-degree angle, unlike the Pelton turbine. These turbines are used at very high rotational speeds because, in contrast to Pelton turbines, they can handle higher flow rates.

The main features of a turgo turbine include the following.

• High flow rates
• Suitable for high speed
• This turbine handles with a high water flow rate
• Simple to assemble

Cross-Flow Turbine

In the year 1903, Donnet Banki, Fritz Osberg, and Anthony Michel created these turbines. These are specialized impulse turbines that are utilized in small hydropower facilities. These turbines have very simple designs but require very little upkeep. Water is supplied axially or radially in some turbines, but across or through the turbine blades in these types of turbines.
The following are the main characteristics of the cross-flow turbine.

• Its design & maintenance is simple
• These turbines deliver water with 20 to 2000 liters per second flow rate from 2m to 200m
• These are used in hydropower plants which have 5 kW to 100 kW power rating & also in large 3 MW power plants.

Advantages

The advantages of an impulse turbine include the following.

• High efficiency
• These turbines have simple construction and maintenance.
• It functions at atmospheric force.
• These turbines have an easy assembly.
• The rotational speed is high

Disadvantages

The disadvantages of impulse turbines include the following.

• It needs a high head which is not easy to handle.
• Large size
• Installation cost is high
• The efficiency will be decreased over time.
• For high flow rates, it is not suitable
• It is suitable for low discharge.

Applications

The impulse turbine uses include the following.

• Used in hydropower plants.
• Impulse turbines are used in drinking water supply systems.
• It is used in Hydro Power Plant.
• This type of turbine is used to generate electrical energy