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How does a hydraulic turbine work?
Mis à jour le
March 6, 2026
5
Min reading
Hydroelectric power plants are true engineering masterpieces that have revolutionized The history of electricity. Even today, hydroelectricity is one of the most important sources of energy in the world.
Hydroelectric power plants essentially consist of reservoirs, dams, forced pipes, generators and turbines. Fed by water, it is undoubtedly the main component of hydroelectric power plants. SirEnergies shows you how hydraulic turbines work.
What is the general function of a hydraulic turbine?
Hydraulic turbines are part of turbomachines and, as a result, they include their three main components :
- the distributor,
- the rotor,
- possibly a diffuser.
Evolution of the water wheel, they are machines whose role is to transform the kinetic energy of water into mechanical energy.
Hydraulic turbine operation
Gravitational potential energy is first converted to kinetic energy. Flowing water is accelerated to a maximum speed within a dispenser.
This makes it possible to operate the rotor of a generator, which in turn is responsible for transforming the stored mechanical energy into electrical energy. Turbines are generally custom-made for each power plant, which ensures maximum efficiency.
The wheel is undoubtedly the main part of the hydraulic turbine. It is it that rotates under the impulse of the force of the moving water. Depending on the water flow and the height of the fall, different hydraulic turbines can be distinguished.
The two main models of hydraulic turbines
Two main models of hydraulic turbines are most often distinguished: the action turbine and the reaction turbine. In an action turbine, the total potential energy is transformed into kinetic energy in the fixed distributor. No pressure drop is observed between the inlet and the outlet of the wheel. More specifically, the exchange of energy takes place under atmospheric pressure.
Likewise, these turbines do not include a diffuser unlike reaction turbines. This element makes it possible to recover part of the kinetic energy at the exit of the wheel and the height that exists between it and the downstream level of the dam. The diffuser creates a vacuum at the outlet of the rotor, which is why it is also called a vacuum cleaner or suction pipe.
In the case of the reaction turbine, the potential energy is partially converted in the distributor and in the rotor. In the latter, we observe A pressure differential between the entrance and the exit. The ensuing flow is then diverted and accelerated in the rotor.
The most popular hydraulic turbines
All the turbines widely used in power plants are action or reaction models. This is particularly the case with the Pelton turbine, the Francis turbine, the Kaplan turbine and the Crossflow turbine.
The Pelton turbine
Pelton turbines are generally used in high-fall power plants (from 130 to 2,000 meters) and low flow power plants. They are well indicated in the case of high mountain dams. The Pelton turbine is an action machine whose axis can be horizontal or vertical. This type of turbine is composed of a moving wheel and a distributor made up of injectors that vary from 1 to 6.
Injectors are converging nozzles that transform Hydraulic power of pressure into kinetic energy. Arranged around the wheel, they emit A jet at atmospheric pressure which is directed towards the middle of the troughs. By varying the output of the needles, it is possible to regulate the flow and to adjust the diameter of the jet.
In a Pelton turbine, the wheel rotates at atmospheric pressure. However, as it passes through it, the water is diverted by almost 180°, which allows it to give up all its kinetic energy. This explains why this type of turbine does not have a diffuser. The presence of a housing is generally sufficient to recover and channel water.
The Francis turbine
Francis turbines are very suitable for fall heights (40 to 730 meters) and average flow rates. They are frequently found in waterside power plants. It's abouta radial type reaction turbine whose axis is vertical.
Its dispenser is wound around the turbine. Water enters from all around its periphery. As for its output, it takes place axially in the diffuser.
The Francis turbine is undoubtedly one of the oldest turbine models and also one of the most widespread. It is found in several possible configurations (horizontal in mini-hydro, in vertical axis). Very robust and effective, it sinks about 2 m below the downstream level. In some cases, the wheel may be located above the latter.
The Kaplan turbine
This type of turbine is very common on falls of low height (5 to 80 m) and with a high flow rate. La Kaplan turbine is an axial-type reaction model. Its axis is vertical and one of its particularities is that it offers the possibility of adjusting the angle of inclination of the blades, which makes it possible to adapt the flow that passes through the turbine to that of the river.
Kaplan turbines are fairly common machines. Their sinking of about 5 m below the downstream level is rather moderate. In addition, the pitch of its blades is adjustable, which means that the efficiency of this turbine is not subject to variations.
One of the variants of the Kaplan turbine is The Bulbe turbine. It is in fact a Kaplan device with a horizontal axis. It was designed for installations with a low fall over the water. Their structure resembles that of a submarine.
The bulb is also characterized by a rather significant depression of the wheel compared to naval level (approximately 10 m).
The Crossflow turbine
The Banki-Mitchell or Crossflow turbine is a turbine in which water is injected into a cylindrical rotor with a horizontal axis that passes through a rectangular convergent. The flow in this type of turbine is diverted in contact with the peripheral blades. The rotor has about thirty curved blades that are fixed and parallel to the axis of rotation.
One of the great strengths of this turbine is its simplicity. In fact, it has only three moving parts: the rotor and the two flow control flaps. However, it most often requires major earthworks.
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