Impulse turbine is one of the simplest turbines out there, classified as hydro turbines along with reaction turbines. These turbines are group based on how the energy is exchanged between the fluid and the turbine. They are installed to convert the potential energy and kinetic energy of water flow into mechanical work. Hydropower plants extensively make use of an impulse turbine and it can be used for water pumping.
Today you’ll get to know the definition, applications, function, components, diagram, types, and working principle of an impulse turbine. You’ll also get to know the advantages and disadvantages of this impulse turbine in its various applications.
What is an impulse turbine?
An impulse turbine is a device that uses the kinetic energy of the fluid to strike the blades through the nozzle. in these turbines, a set of rotating machinery operates at atmospheric pressure. They are suitable for high head and low flow rates. Impulse turbines work based on the change of velocity vectors, that is, the potential energy of the water (or other sources of fluid, e.g., steam) depending on the height of the waterfall is converted into kinetic energy by one or more nozzles.
When the water hits the turbine blades at high speed causing the turbine to spin and a shaft connected to the generator will allow the electricity to generated. This makes it suitable for extracting energy from the high head and low flow conditions.
Impulse turbines are of three types, Pelton, Turgo, and Cross-flow. The construction of Pelton and Turgo turbines is much similar. However, a Cross-flow turbine is a modified version of an impulse turbine, classified as an impulse turbine. This is because of the rotation of the runner at atmospheric pressure and not as a submerged turbine.
Applications of impulse turbine
The applications of an impulse turbine are widely used for electrical power generation. In fact, a large proportion of the world’s electrical power is generated by turbo generators.
The space shuttle main engines used turbopumps (a machine that consists of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine’s combustion chamber.
Water turbines are used in hydroelectric powerplants. They use water as their working fluid. Finally,
Steam turbines are used in nuclear and thermal power plants. Water is heated to form steam and then flowed through turbines to produce electricity.
Note: the primary function of an impulse turbine is for power generation and water pumping.
Components of impulse turbine
Below are the major components of an impulse turbine as well as their functions:
This part in an impulse turbine is like a circular disk containing a number of curved blades attached to it. There is a cylinder shaft in the center which is made of stainless steel as well as the runner. Well, the runner can be made of cast iron when the flow head is less.
The buckets are like a set of spoon-shaped cups that are mounted around the runner to exchange energy between the fluid and the turbine. The fluid at high speed hits these buckets after leaving the nozzle, causing the turbine blades to rotates and exiting the outer edge of the bucket. The turbine design will determine the change in the direction of the fluid during the exit compared to the angle of impact. The largest momentum is gotten at an angle of 180 degrees.
The function of a nozzle in an impulse turbine is to adjust, modify and jet the fluid flow to strike the buckets. It is one important part of this turbine that causes pressure changes and allows the flow head to be converted into kinetic energy. A part called spear in this device is used to adjust the volume of the water jet reaching the buckets. These nozzles are designed from a tungsten carbide, which is very hard and can withstand erosive particles.
Casing in an impulse turbine serves as a shield over the turbine to prevent water from splashing out. It also guides it to the spillway, which exists for the extra water to protect the structural integrity of the dam. Generally, this part is produced with cast iron.
The part is widely used in hydropower plants as pipes and channels that convey water from dams and reservoirs o turbines. Water flows in it at very high pressure. penstocks are normally made of steel
Diagram of impulse turbine:
Types of impulse turbine
Below are the various types of impulse turbine used in hydropower plant as well as their working:
A Pelton turbine has its major components as runner, nozzle, and deflector. It is used for high water drop height. One or more nozzles (up to 6) help in converting the water head to high-speed flow. As the water flow, consequently, the power of the turbine is controlled by regulating the water flow quantity.
The system features a series of buckets symmetrically around the cylindrical runner of the turbine. The design and shape of these buckets cause the water jet to hit the center of the bucket and come out from both sides. This exit occurs in a way that the water coming out of the bucket does not hit the next one, resulting in a brake. The axis of the turbine wheel can be mounted vertically or horizontally. For high powers, efficiency, and a higher number of nozzles, the wheel shaft is always vertical, and the generator is installed above the turbine.
A deflector is located between the runner and the nozzle. It helps to prevent water from spraying from the nozzle to the buckets when the load is suddenly removed from the turbine. This increases its rotational speed. Finally, a spear is used to stop the flow of water.
Diagram of Pelton impulse turbine:
The turgo types of impulse turbine operate similarly to that of Pelton. Their major difference is that the water jet hits the buckets obliquely (about 20 degrees). This is because the shape of the bucket is complicated and more difficult to manufacture. Turgo turbines have a higher specific speed than Pelton. One advantage of these types of impulse turbines is the larger jet and a smaller machine size compared to Pelton for equal power. Small hydropower plants make use of this turbine.
Diagram of Turgo impulse turbine:
These types of turbines are the modification of impulse turbines often used in small hydropower plants. Just like impulse turbines, the rotor is rotating in air and not fully submerged like a reaction turbine. The benefits of this turbine include operation in a wide range of flow rate, head, and consequently power. Furthermore, it can adapt well to changes in flow while saving efficiency. There is a special control system that can adjust the active part of the turbine according to the amount of water flow.
Diagram of a cross-flow turbine:
Working principle of an impulse turbine
The working of an impulse turbine is different since there are various types out there. well, while explaining the various types I mentioned how they work. Generally, in the power generation process in impulse turbines, the following steps must be accomplished.
- The stored water flows from a source upstream through Penstock to be delivered to the nozzle.
- The potential energy of the water inside the nozzle is converted into kinetic energy and injected into the blades or buckets; thus, the runner spins.
- There is a mechanism to control the flow of water injected into the runner. The spear usually plays an important role in this process.
- The generator attached to the shaft converts mechanical energy into electrical energy.
Watch the video below to learn more on the working of an impulse turbine:
Advantages and disadvantages of an impulse turbine
Below are the benefits of impulse turbines in their various applications.
- Easy to maintain.
- Simple construction.
- High working efficiency.
- Can works at atmospheric pressure.
- Its rotational speed is high.
Despite the good advantages of an impulse turbine, some limitations still occur. Below are the disadvantages of an impulse turbine in its various applications.
- It occupies a lot of space due to its size.
- The installation cost is high.
- Working efficiency decreases over time.
- Not suitable for high flow rates.
- Ideal only for low discharge.
- It requires a high head which is difficult to manage.
Impulse turbines are special types of turbines for power generation and water pumping. They are of three types including Pelton, Turgo, and cross-flow. that is all this post where the definition, applications, function, components, diagram, and working of an impulse turbine was explained. Its advantages and disadvantages were also stated.
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