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Hydraulic turbines

Hydraulic turbines

A turbine is a turbomachine that converts the energy of flow of a fluid (liquid or gas) into mechanical energy by means of a system of rotating blades. This mechanical energy can be used to power another machine or an electric generator.

The turbine name was proposed by Claude Burdin during an engineering contest in 1828. This name comes from the Latin turbine, which means Foucault current.

A simple turbine consists of a single rotor with vanes, which provide exchange of energy with the flow. The first examples of turbines are wind turbines and water mills (wind power and hydropower).

Gas, steam and water turbines generally have a housing around the rotor. This casing drives the flow in the desired direction, which benefits the efficiency. Steam turbines are used in certain solar thermal power generation facilities. This type of turbines are also used in thermal power plants that use fossil fuels or in nuclear power plants

The back of a turbine is a compressor. The compressors are used in some gas turbines and are available in two configurations: the radial compressor and the axial compressor, which are named after the direction in which the fluid flows during compression.

Types of hydraulic turbines

Hydraulic turbines, used in hydraulic power installations, can be classified according to two criteria. A first classification according to how it works and a second classification of turbine depending on the design.

Regarding the way it works, the hydraulic turbine can be classified into two groups:

  • Hydraulic action turbines: they only take advantage of the speed of the water flow.
  • Hydraulic reaction turbines: take advantage of both the speed and the pressure loss of the water inside the turbine.

Depending on the design of the turbine rotor, the following types of turbine can be differentiated:

  • Propeller turbine: axial-type reaction turbines, like a propeller placed on the horizontal pole.
  • Kaplan turbine: axial type reaction turbines, they are like propeller turbines that can also vary the angle and the blades of the propeller during its operation. They are more efficient with large flows and small waterfalls.
  • Pelton turbine: turbines with transverse flow action (turbine vertically) and partial admission. They are an evolution of water mills. They are designed to work with very large waterfalls but with small flow rates.
  • Francis turbine: reaction and mixed flow turbines. Designed for waterfalls and average flow rates.

Pelton Turbine

One of the most efficient types of hydraulic turbine is the Pelton turbine. The Pelton turbine consists of a wheel (impeller or rotor) equipped with spoons on its periphery. These spoons are specially designed to convert the hydraulic energy of a water jet that hits the spoons.

Pelton turbines are designed to exploit large low flow hydraulic jumps. Hydroelectric plants equipped with this type of turbine have, for the most part, a long pipeline called a pressure gallery to transport the fluid from great heights.

At the end of the pressure gallery, the water is supplied to the turbine by means of one or several needle valves, also called injectors, which are nozzle-shaped to increase the speed of the flow that hits the spoons.

Francis turbine

The Francis turbine was developed by James B. Francis. It is an internal flow reaction turbine that combines both radial flow and axial flow concepts.

The Francis turbine is what is called a "reaction" turbine, since the impeller element (usually water) is applied through it, and it is the same circulation of the impeller that makes it move. It is one of the three main families of turbines ( Pelton, Francis and Kaplan).

It consists of a fixed part, with curved guides called deflectors (or distributor), and a mobile part with blades, also curved, called a rotor. The inclination of the deflectors can be adjusted to adjust the flow rate applied to the blades, thus regulating the speed of the turbine.

It is a type of turbine very appropriate for medium-high jumps with medium flow, being able to produce very high powers.

Kaplan turbine

Kaplan turbines are axial flow reaction water turbines, with a roller that works similar to a ship's propeller. They are used in hydraulic power installations with small height jumps. The wide blades or blades of the turbine are driven by high pressure water released by a gate.

The water circulates in the same direction as the axis. In addition to being able to regulate the inclination of the baffles, the rotor vanes can also be adjusted, so that the turbine adapts to the power needs of each moment. It is used in renewable energy facilities of hydraulic type for small jumps and large flows, such as those of reservoirs.

Propeller turbine

Like all hydraulic turbines the turbine propeller consists of a steering wheel with guide vanes and a rotor. Depending on the flow, the helical turbine can be made with simple adjustment (adjustment of guide vanes) or double (adjustment of guide vanes and speed of rotation of the rotor).

The guide vanes adjust the volume of flow that enters the rotor. At the same time they change the flow direction so that the rotor enters the torsion itself so the rotor rotates.

The rotor of a turbine propeller has 3-5 blades connected fixed to the rotor shaft. According to the theory of flow of a vane there is an ideal flow for the ideal efficiency of a vane. As the flow and height of fall of the water entering the turbine is not constant, the rotor blades must be adjusted to the actual flow. The actual flow is characterized by pressure (potential energy) and velocity (kinetic energy) that vary according to the volume of the river, the times or the regulation of dams river abajao. To maximize the efficiency of the turbine, the rotation rotation of the rotor is adapted to the characteristic of the flow. This principle requires a synchronous generator and a current conversion to adjust it for the supply of the network.

On the contrary, the regulation principle of a Kaplan turbine is the adjustment of the rotor blades (mechanical regulation).

From the efficiency point the turbine propeller can be compared to a Kaplan turbine. In addition, the electronic regulation of a turbine propeller (regulation of rotor speed) allows to achieve points of operation with little water that can not be achieved with a Kaplan turbine. That's because the Kaplan turbine operates with constant speed and when there is not enough water you can not maintain the high speed of rotation. The turbine propeller still supplies with low speed of rotation.

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Last review: October 25, 2018