Kaplan-Turbine

The Kaplan turbine is an axially flowing water turbine with adjustable impeller and is used in hydroelectric power plants. It was further developed by the Austrian engineer Viktor Kaplan in 1913 consisted of a Francis turbine and patented. Cavitation occurs particularly easily in this type of turbine resulted in the development work always be setbacks. The first Kaplan turbines could only go into a successful continuous operation, as you knew how to combat this phenomenon by structural measures on the turbine into the handle.

Principle of operation

The impeller resembles a ship's propeller, whose wings are adjustable at the Kaplan turbine. Turbines without this blade adjustment are called propeller turbines. However, should a relatively constant amount of water available for the use of a propeller turbine available, since the efficiency at partial load drops rapidly. The water is mixed with a spiral twist, and the stabilizer, also referred to as guide vanes, ensures that the water hits the blades parallel to the shaft, thereby transferring the energy. The water pressure decreases from the inlet into the impeller to the discharge steadily. The Kaplan turbine is therefore a reaction turbine. Through the suction pipe, the water leaving the turbine.

Installation is usually vertical so that the water flows from the top downwards. Directly above the turbine, the alternator is usually appropriate to be able to transfer the heat generated by the impeller kinetic energy through a vertical shaft without deflection losses to the generator rotor can. The achieved efficiency is in the range of 80-95 %. The adjustable guide vanes impeller and the Kaplan turbine can be regulated. Thus, it can be better adjusted to the respective amount of water and height of fall. It is ideally suited for use in low to lowest heads and large and fluctuating flow rates. The Kaplan turbine is therefore predestined for large -river power plants to calm flowing bulk waters.

Developments

Kaplan bulb turbine

From the Kaplan turbine the Kaplan bulb turbine for low heads up to 25 m and a power has been developed up to 75 MW, whose shaft is fitted with wheel horizontally in the direction of the flowing water. This deflection losses are avoided, thus achieving a greater absorption capacity and a higher full- load efficiency. The generator is housed in a waterproof case on the extended end of the turbine shaft. The horizontal arrangement, a smaller footprint and thus a lower overall height of the nacelle is possible, so the landscape is less affected.

Model of Kaplan bulb turbine with generator ( front view) in the historic water plant at high drain

Kaplan bulb turbine with generator ( small power plant ).

Special forms of Kaplan bulb turbine are the S- turbine ( for fall heights up to 15 m ) and the transmission tube turbine ( for fall heights up to 12 m ). The S- turbine the suction pipe is bent S-shaped and the turbine shaft is guided from the turbine housing. The generator is allowed to install outside of the turbine and is therefore more accessible to regular inspections and maintenance. The overall height can be reduced even further. This also makes the installation of the turbines in small hydropower plants, for example, across a narrow river or canal, with fall heights up to 5 m or light impoundment possible by a weir. See also types of hydropower plants. S- turbines are used in power plants up to a capacity of 15 MW. The transmission tube turbine is similar to the S- turbine strong, but it differs in two essential features. The suction pipe is straight and the turbine shaft is connected through a gear instead of directly to the generator. This can take place horizontally or vertically, whereby the more compact design compared to the S- turbine failure. By a suitable over-or step-down the turbine speed can be optimally adapted to the generator. Transmission tube turbines are used in power plants with a capacity up to 4 MW.

S- turbines, Augsburg used at high discharge for power generation, for example, in the historic waterworks. With the electricity generated, the pumps are operated for water supply and covered the own needs of the waterworks. The " excess power " is fed into the public power grid. Clearly visible is the impeller with its adjustable wings, the mechanism ( yellow) for adjusting the guide vanes and the s- shaped intake manifold. The inlet of the turbine is formed by the funnel-shaped inlet with the cone-shaped tail. The transparent Plexiglas walls are of solid masonry.

Straflo turbine

A further development of the Kaplan bulb turbines are the so-called Straflo turbines (of English. Flow straight, straight flow ). In this type of turbine the rotor of the turbine and the rotor of the generator form a unit, which lie in a common plane. Thus, the Straflo turbine does not have a wave, instead carrying the turbine blades of a peripheral, in which the excitation winding is integrated. In contrast, the stator winding is installed in the casing of the turbine; it is in the water, which drives the turbine. The mounting of the turbine axis is done on one side in a sealed housing.