# Understanding reaction turbine

Being a special type of turbine used in hydro-power plants, reaction turbine is used all around the world for the generation of electricity. It is estimated that about 60% of turbines used in hydro-power plants are reaction turbines, though still in competition with impulse turbines. A reaction turbine is constructed of rows of fixed blades and rows of moving blades. These fixed blades act as nozzles and the moving blades move as a result of the impulse of steam received (caused by a change in momentum). Also, as a result of expansion and acceleration of the steam relative to them, still acting as nozzles. This will be further explained, stick with me!

Today you’ll get to know the definition, applications, function, components, diagram, types, and working principles of a reaction turbine. You’ll also get to know the advantages and disadvantages of this reaction turbine.

Contents

## What is a reaction turbine?

A reaction turbine works with Newton’s third law of motion (action and reactions are equal and opposite). The system generates torque in response to the fluid’s pressure and weight. In it working, water first strikes the fixed blades then strikes the nozzle.

In a reaction turbine, the sum of potential energy and kinetic energy of water due to the pressure and velocity, respectively causes the turbine blades to rotate. The entire body of this turbine is immersed in water and changes in water pressure along with the kinetic energy of the water cause power exchange. Applications of a reaction turbine are usually at lower heads and higher flow rates than impulse type.

The turbine blades or impeller blades are designed to be able to generate a force on one side when water flows through it just like an airfoil. In an airplane, the force produced by an airfoil is responsible for its lifting. Similarly, here, the force causes the blades to rotate.

Different types of reaction turbines have their own ideal operating conditions. For examples,

• Pelton turbines are preferred where a low discharge rate can be obtained & a high head(80-1600m) is available.
• Kaplan turbines require a high discharge rate along with a low or medium head(2-70m).
• Francis turbine work on medium flow rate & medium head. Francis turbine is a combination of impulse & reaction turbines.

Francis turbines are the most widely used turbines because they offer the highest efficiency & could also work in a wide range of operating conditions.

## Applications of reaction turbine

The various applications of a reaction turbine include the following:

• Wind power mills to generate electricity.
• Also, for electricity generation in hydro-power plants.
• Reaction turbines are used to obtain maximum power output from a low available water head and high velocity.

Note: the primary function of a reaction turbine is for power generation.

## Components of reaction turbine

Below are the major components of the reaction turbine and their function.

### Spiral casing:

these components of the reaction turbine have a uniformly decreasing cross-section area, along the circumference. This decreasing cross-section area ensures a uniform velocity of water striking the runner blades. There is an opening for water flow into the runner blades from the starting of the casing, causing pressure to decrease as it travels along with the casing. The reduction of its cross-section area along its circumference to make pressure uniform, therefore, uniform momentum or velocity striking the runner blades.

### Guide vanes:

Guide vanes are mounted in the spiral casing to ensure the water striking the runner blades have direction along the length of the axis of the turbine. Otherwise, the flow would be highly swirling as it moves through a spiral casing, making it not efficient enough to rotate runner blades. In modern turbines, the angles of these guide vanes are adjustable, making the water flow rate adjustable.

Runner blades are important components of a reaction turbine. In fact, it is considered the heart of the reaction turbine. The shape of the runner blades uses the pressure energy of water to run the turbine. Their design is very essential and plays a major role in deciding the efficiency of a turbine. In the modern version, these blades can pitch about their axis, thus, the pressure force acting on them can vary according to the load and available pressure.

### Draft tube:

A draft tube connects the runner exit to the tailrace, having an increased cross-section area along its length. Water coming out of runner blades is at considerably low pressure, its expanding cross-section area recovers the pressure as it flows towards the tailrace.

## Types of reaction turbine

Below are the various types of reaction turbine

### Propeller turbines:

Propeller types of reaction turbine usually have a 3 to 6 blade flow path, having the water in constant contact with all of the blades. Propeller turbines can only be installed at the place where load and height are constant. Its energy efficiency curve is very peaked under partial load. Which means, poor performance in the system.

Kaplan turbines can achieve high-efficiency levels under various load conditions by properly adjusting the blades during their working. This is because the blade angle can be adjusted to the required power.

Read more: Different types of turbine

### Francis turbines:

These types of reaction turbine are a modified version of the propeller turbine, as the water flowing radially and axially into the runner. In its working, the flow channels are generally set in spiral housing with internally adjustable influence blades.

These types of reaction turbines have a rotor that has nine or more fixed blades. Water initiates directly above and around the runner, which then falls and turns.

### Gravity turbines:

These reaction turbine types convert gravity force into rotational force. So, in its working, the kinetic energy of the gravity force is converted into electricity.

### Bulb turbines:

Bulb turbine types are variants of propeller turbines. The bulb turbine generator is enclosed and sealed in a streamlined watertight steel housing located in the duct center. This generator is driven through a variable pitch propeller at the downstream end of the valve. The direction of water entering and exiting the system is practically unchanged or very little. Its compactness offers more flexibility in powerhouse designing.

### Straflo turbines:

These reaction turbine types are axial turbines with fixed blades. Its generator is located outside the water channel and is connected directly to the turbine runner.

### Tube turbines:

In this reaction turbine, the pressure line is bent shortly after and before the flow path, enabling a straight connection to the generator.

## Working principle of reaction turbine

The working of a reaction turbine is less complex and can be easily understood. In its working, a rotor containing moving nozzles that releases water of high pressure. As the water leaves the nozzles, they experienced a reaction force that rotates the rotor at a very high speed. Also, a reaction force is generated by the fluid moving on the runner blades. The reaction force produced on the runner blades causes the runner to rotate. The fluid enters the draft tube after moving over the runner blades and then finally to the trail race.

#### Watch the video below to learn more on the working of reaction turbine:

Below are the benefits of the reaction turbine its various applications:

• High hydraulic efficiency.
• High working speed.
• Design is less complex.
• Less space is required.
• Uses an oil-free exhaust system.
• Portable in size.
• Capable of using high temperature and pressure.

Despite the good advantages of a reaction turbine, some limitations still occur. Below are the disadvantages of a reaction turbine in its various applications.

• Require high maintenance
• Cavitation issues occur.
• The maintenance cost is high.
• Thrust force is generated.