How Does An Impulse Turbine Work? | An-Overview
A turbine is a device that uses to produce electricity. There are multiple types of turbines, and impulse turbine is one of them. According to the design of impeller blades and nozzle, turbine divides into two major types;
- Reaction Turbine
- Impulse Turbine
In the previous article, we discussed reaction turbines. This article just focuses on the impulse turbine working principle and some other aspects.
What is Impulse Turbine?
An Impulse turbine is a very famous category of turbine in which a jet of water pushes the rotor and the water jet collides directly with the rotor 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.
The impulse turbine has multiple static nozzles that convert the pressure of the water jet into kinetic energy. After passing through the nozzle, the water strikes the blades of the impeller. The turbine impeller blades get almost all of the kinetic energy of the water jet and convert it into water speed. These turbines use for low water flow rates and high head functions.
The main difference between reaction turbines and impulse turbines is that in an 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.
The impulse turbine works on the following simple steps:
- A jet of water moves from a reservoir or dam to the fixed nozzles of the turbine.
- As the water enters into the nozzle, it converts the pressure energy of the water into kinetic energy.
- After discharging through the nozzle, the water jet hits the impeller blades and rotates the impeller along its own axis.
- The impeller blades transform the kinetic energy of the water jet into speed and increase the speed of the water.
- This high-speed water strikes the turbine due to which the turbine shaft starts rotating.
- This turbine shaft links with the coil of the generator. The rotary motion of the turbine shaft uses to rotate the coil of the generator.
- As the generator coil starts rotating, it produces electricity. This produced electricity delivers to 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.
So, it recommends using 3-4 nozzles instead of one. In this way, the turbine’s power output capacity will be increased and also turbine can bear heavy load. When the turbine load is small, turn off some water jets to adjust the power.
If the turbine load drops sharply and the spear can’t regulate the water jet flow quickly. 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 Blades
The impeller blade has a cup-shaped hollow hemispherical construction. It screws on the top of the impeller. The buckets include in the major components of the impulse turbine. The jet hits these blades and turns the impeller. These blades design in such a way that they transform the kinetic energy of the water into speed and increases the water speed. The blade’s design acts an important role in determining the turbine efficiency. These are made of cast iron or stainless steel.
2) Runner or Impeller
The runner of the turbine is a solid disc centered on a cylindrical shaft. 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 from cast iron where the usable head of the water is minimal, so the force acting on the turbine is not too high.
3) Casing
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.
4) Nozzle
The purpose of the nozzle is to direct the water flow towards the impeller blades. The water from the dam flows inside a nozzle which converts the pressure energy of the water into kinetic energy. After this conversion, it sends increased kinetic energy water to the impeller where water strikes the impeller blades.
5) Spear
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:
- Pelton Whell Turbine
- Turgo Turbine
- Cross-flow Turbine
1) Pelton Wheel Turbine
This turbine uses for a high head of water. During the operation of the Pelton Wheel turbine, 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 on the centre (deflector) of the vanes and emerges from both ends. Due to the turbine design, the exit water from one vane doesn’t hit the next one 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
- These turbines can discharge water from 5-1000 liters/second.
- Pelton turbines are easy to install compared to reaction 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
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. |
Advantages and Disadvantages of Impulse Turbine
| Advantages | Disadvantages |
|---|---|
| It has easy maintenance. | Its size is large as compared to other turbines. |
| Its construction is very simple. | It requires a high head which is difficult to manage. |
| The efficiency of the impulse turbine is high. | The efficiency decreases over time. |
| These turbines have an easy assembly. | High installation costs. |
| It works at atmospheric pressure. | It is not the best turbine for high flow rates. |
| It has a high rotational speed. | It is good only for low discharge. |
FAQ Section
Why It is called Impulse turbine?
These turbines are known as impulse turbines because, in these turbines, water generates impulse force instead of reaction to turn the turbine.
What is impulse turbine give example?
The impulse turbine has the following examples:
- Cross-flow turbine
- Pelton wheel turbine
- Turgo turbine
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.
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