This article focuses on the impulse turbine working principle and some other aspects. So, an Impulse turbine is a very famous category of the turbine in which a jet of water pushes the rotor and the water jet collides directly with the blades. Impulse turbines are the most accessible form of the turbine. It contains a series of blades and a series of nozzles. Nozzles and blades are the major components of an impulse turbine. This type of turbine has multiple fixed nozzles that can convert pressure like a liquid jet into kinetic energy. Mostly water uses as a liquid in the turbine. The jet hits the moving plate of the turbine impeller, which absorbs almost all of the kinetic energy of the water. These turbines use for low water flow rates and high head functions.
There are two main types of these turbines: the Pelton wheel turbine and the Targo turbine. The main difference between reaction turbine and impulse turbines is that in impulse turbine all hydraulic energy of the water is transformed into K.E through nozzles. And there is no pressure change during the process. In contrast, in reaction turbines, only a certain amount of existing energy is transformed into kinetic energy.
Impulse Turbine Working Principle
The impulse turbine working principle is according to the basic impulse principle. Newton’s second law of motion explains the impulse turbine working principle. For these turbines, the water stores in high places and flows through nozzles, which are mainly above or below the ground. So, the nozzle converts the stored water energy into a high-velocity water jet. This high-velocity jet hits the buckets fastened to the flow impeller and rotates the impeller along its own axis. In this way, the high-speed water jet energy transforms into the rotational energy of the tribe shaft. This rotary motion of the turbine shaft uses to rotate the coil of the generator. And the coil rotation generates electricity from the generator. This produced electricity transforms into different industries and houses.
Depending on the load on the turbine, the spearhead moves all through the nozzle to control the water flow. To get the highest yield from the turbine, the speed of the water-jet should be two times as compared to the velocity of moving blades. Thus, the water injection rate adjusts according to the speed and load of the turbine, and the turbine continues to operate in the most effective range.
Similarly, use 3-4 nozzles instead of one. This is done to cope with high turbine loads and to improve turbine performance. When the turbine load is small, turn off some jets to adjust the power.
If the turbine load drops sharply and the spear cannot regulate the water jet flow fast adequate. Due to this reason, the turbine speed will continue to increase and the turbine may be damaged. To avoid this, a deflector uses to divert the flow of water away from the turbine blades. It Keeps the turbine in a safe area.
Major Components of Impulse Turbine
1) Buckets or Vanes
The vane has a cup-shaped hollow hemispherical construction. It screws on the top of the impeller or runner. The buckets include the major components of the impulse turbine. The jet hits these buckets and turns the runner. Its design acts an important role in determining the turbine efficiency. Blades are made of cast iron or stainless steel.
The runner of the turbine is a solid disc centred on a cylinder axis. The impeller and the shaft made of high-strength stainless steel. Due to this reason, the load on the turbine is quite high. The impeller also manufactures cast iron and the usable head is low, so the force acting on the turbine is not too high.
The casing involves in the basic components of the impulse turbine. It is a type of protective shield for the turbine. Mostly it protects the turbine from damage when a heavy thing falls on it. It is generally built of cast iron. It stops the splashing of water and directs it into the overflow path.
The purpose of the nozzle is to direct the water flow towards vanes. It also increases the speed of the water jet that comes from a high head. Nozzle converts the potential energy of water into kinetic energy.
The spear has a conical structure that allows to control the water flow in and out of the nozzle and hit the bucket. It controls water flow by its back with forth motion in the nozzle. The spear attaches to the nozzle. It includes in the main components of the impulse turbine.
Impulse Turbine Types
Impulse turbine has the following three major types:
1) Pelton Wheel Turbine
Main article: Pelton Wheel Turbine
This turbine uses for a high head of water. During this process, one or more nozzles convert the water head into a high-speed stream. By adjusting the water flow capacity, you can control the turbine power.
Pelton turbine has a series of vanes that are mounted symmetrically around the cylindrical impeller. Due to the special shape of these vanes, the water jet hits the centre (deflector) of the vanes and emerges from both ends. This outlet prevents water from one vane from hitting the next and does not slow down.
The deflector of this turbine is mounted between the nozzle and the impeller. The deflector prevents water from leaking from the nozzles to the vanes when the load unexpectedly removes from the turbine and its speed increases. Then the water flow slowly stops by a spear.
Pelton turbines have some other features that are given below:
- These turbines use for heads from 20-100 meters and discharge 5 to 1000 liters/second.
- Pelton turbines are easy to install compared to reactive turbines of similar performance. This is because the Pelton turbine has a relatively low flow rate, and the required pipes are also small.
- These turbines operate with high water head, due to that these turbines require complex and expensive Penstock.
- These turbines can attain an efficiency of up to 95%. Small hydropower plants can attain efficiencies of up to 90%.
2) Turgo Turbine
Turgo impulse turbine is almost similar to Pelton turbine. The main difference between these turbines is that the Turgo turbine uses a single cup instead of a double cup in the hub, and these cups have a more flat shape. In the Turgo turbine, the water jet hits the vanes diagonally (approx. 20 degrees).
Pelton impulse turbines have a lower definite speed than Turgo. Compared to the same power Pelton turbines, Turgo turbines have a small machine size and large water jet. This type of impulse turbine is used in micro hydropower plants.
Some more features of Turgo turbines are given below:
- They have higher flow rates than Pelton turbines of the same size.
- Appropriate for high speeds.
- This turbine can handle a greater water flow rate.
- These turbines are easy to assemble.
3) Cross-Flow Turbine
Main article: Cross-Flow Turbine
A cross-flow turbine is an improved impulse turbine used in micro-hydroelectric powerplants. One of these turbines’ main features and benefits is their ability to operate over a wide range of flow rates, heads, and powers. Moreover, it can adjust well to various inflow while reducing efficiency. A particular control system can regulate the moving parts of the turbine according to the water flow.
This turbine has a drum-shaped impeller. When the head is high, the impeller is short, and when the head is low, the impeller is long. the water arrives in the turbine after passing through the inlet adapter and guides buckets, which directs the water flow and hitting the rotor at the correct angle for maximum efficiency. After departing through the impeller twice, the water leaves the turbine through the outlet valve.
The major features of cross-flow turbines are given below:
- These turbines can be used for delivery heads of 2m to 200m with a flow rate of 20 to 2000 liters/second.
- Easy to manufacture and low maintenance.
- These turbines used in hydropower plants have a power range of 5 kW-100 kW typically, in large plants up to 3 MW.
Applications of Impulse Turbines
1) It uses in the drinking water supply system.
2) These turbines use in hydropower plants.
What is the difference between a Reaction Turbine and an Impulse Turbine?
|Reaction Turbine||Impulse Turbine|
|More maintenance is required for it.||It requires less maintenance.|
|Only some quantity of the hydraulic energy is transformed into K.E.||The total amount of hydraulic energy is transformed into K.E.|
|Water flow is an axial and radial direction to the turbine wheel.||The direction of the flow of water is tangential to the turbine wheel.|
|Its degree of reaction is among ‘0’ to ‘1.’||Its degree of reaction is zero.|
|It requires high and medium water discharge.||It requires low water discharge.|
|Reaction turbine works at low and medium water heads.||It works at the high head.|
|The reaction turbine has comparatively high hydraulic efficiency.||Impulse turbine has comparatively less efficiency.|
|Francis and Kaplan’s turbine are its example.||Pelton Wheel turbine is its example.|
|Water enters around the impeller.||Water is admitted only in the form of jets.|
|The runner must be closed in a water-tight casing.||In these turbines, casings are not compulsory. Casing works as a safeguard.|
|Velocity and pressure vary as the fluid passes
by the impeller. The pressure at the suction point is much more than the discharge point.
|The velocity of the jet varies the pressure through the remaining atmospheric.|
|The flow control takes place via the guide vane. Other important parts are scroll casing, stay ring, runner, and the draft tube.||The flow control takes place via a needle valve fitted into the Nozzle.|
|Water fully fills at the passage between the buckets and, while flowing between inlet and outlet sections, do work on the blades.||The turbine does not run entirely, and air has free access to the buckets.|
|The reaction turbine has not symmetrical blades.||Impulse turbine has symmetrical blades.|
|The pressure of water is decreased during its flow.||The pressure of water remains constant during its flow.|
|It has high working speed than an impulse turbine.||It has low working speed than a reaction turbine.|
|The efficiency of buckets is high.||The efficiency of buckets is low.|
|These turbines require less space.||It requires high space as compare to the reaction turbine.|
|Newton’s 3rd law defines the energy transfer from reaction turbines.||Newton’s 2nd law defines the energy transfer from impulse turbines.|
What are the advantages and disadvantages of an Impulse Turbine?
1) It has easy maintenance.
2) Its construction is very simple.
3) The efficiency of the impulse turbine is high.
4) These turbines have an easy assembly.
5) It works at atmospheric pressure.
6) It has a high rotational speed.
1) Its size is large as compared to other turbines.
2) It requires a high head which is difficult to manage.
3) The efficiency decreases over time.
4) High installation costs.
5) It is not the best turbine for high flow rates.
6) It is good only for low discharge.
In this article, we deeply discuss the impulse turbine working principle and some other major aspects. So, if you have any questions then let me know without any hesitation. I will try my best to give you a good response.