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There are two main types of hydroelectric turbines: reaction turbines and impulse turbines.

The type of hydroelectric turbine selected for a project is based on the level of standing water - known as "fall" - and the flow, or volume of water over time, at the site. Other decisive factors are how deep the turbine must be set, the efficiency of the turbine and costs. Here are some of the most commonly used turbines in the United States today.

reaction turbine

A reaction turbine creates electricity from the combined forces of pressure and moving water. A runner is placed directly in the water stream, allowing water to flow over the blades instead of hitting them individually. Reaction turbines are generally used for low head, high flow sites and are the most common type used in the United States today.

The two most common types of reaction turbines are propellers (including Kaplan) and Francis. Kinetic turbines are also a type of reaction turbine.

propulsion turbine

A propeller turbine usually has an impeller with three to six blades. Water constantly comes into contact with all blades. Imagine a boat propeller running on a tube. Through the tube the pressure is constant; if that were not the case, the runner would have lost his balance. Blade pitch can be fixed or adjustable. Major components other than the impeller are a volute housing, sliding flaps and a suction tube. There are different types of propulsion turbines:

Francis-Turbine

The Francis turbine was the first modern hydroelectric turbine and was invented in 1849 by British-American engineer James Francis. A Francis turbine has an impeller with fixed blades, usually nine or more. Water is introduced just above and around the rotor, which then drops causing the blades to spin. Other important components besides the impeller include a volute, sliding flaps and a suction tube. Francis turbines are commonly used for medium to high height situations (130 to 2000 feet), although they have also been used for low heights. Francis turbines work well in both horizontal and vertical orientations.

kinetic turbine

Kinetic energy turbines, also known as vortex turbines, generate electricity from the kinetic energy present in flowing water, rather than the potential energy of the head. The systems can be operated in rivers, man-made channels, tidal waters or ocean currents. As kinetic systems utilize the natural path of water flow, they do not require water to be diverted through artificial canals, riverbeds or pipelines, although they may find application in such conduits. Kinetic systems do not require major civil works as they can use existing structures such as bridges, escape lanes and canals.

IMPULSE TURBINE

An impulse turbine generally uses water velocity to turn the impeller and discharges at atmospheric pressure. A jet of water hits all the buckets in the hall. With no suction at the bottom of the turbine, water exits the turbine housing after reaching the impeller. An impulse turbine is generally suitable for high head, low flow applications. The two main types of impulse turbines are Pelton and cross-flow turbines.

Pelton-Turbine

The Pelton turbine was invented by an American inventorLester Allan PeltonIn the 1870s, a pelton wheel had one or more free jets that discharged water into a ventilated space and collided with buckets in an aisle. Pelton turbines are generally used for very high heads and low flows. Draft tubes are not required for an impulse turbine because the rotor must be located above the maximum head to allow operation at atmospheric pressure.

cross flow turbine

The original cross-flow turbine was designed by Anthony Michell, an Austrian engineer, in the early 20th century. Later, Hungarian engineer Donát Bánki improved it and German engineer Fritz Ossberger improved it further. A cross-flow turbine is drum-shaped and uses an elongated rectangular-section nozzle directed against curved blades in a cylindrical-shaped impeller. It resembles a "squirrel cage" blower. The cross-flow turbine allows water to flow through the blades twice. On the first pass, water flows outside the vanes; The second pass goes inside out again. A guide vane at the turbine inlet directs the flow to a limited part of the impeller. The cross flow turbine is designed to accommodate higher water flows and lower loads than the Pelton turbine can handle.