Water turbine
A water turbine is a turbine which makes the hydropower available. Thereby the kinetic energy of the water is converted into mechanical energy by means of the water turbine, which causes rotation of the turbine shaft. This rotation can be used for driving the transmission gear, but more often it is used to drive a generator to produce electricity.
Technical Basics
The power P ( in kW) of a water turbine is calculated in the so-called turbine equation from the efficiency of the turbine multiplied by the density of water ( kg/dm.sup.3 ), g the gravitational acceleration (m/s2), the drop height h (m) and the volume flow ( m3 / s)
The efficiency varies depending on the type, age and operating point of the turbine. New Francis turbines achieve efficiencies of just over 94 %, that is to say 0.94.
The drop height h does not correspond to the actual height between the upper water and underwater. In it, the losses have been accounted for by the friction of the water in the pipes. She has nevertheless the unit meters.
Can illustrate you look at this relationship by using the same formula for a pump that pumps the water from the lower to the upper water. Performs one of these pump mechanical performance, so that turns her wheel, the efficiency from the ratio of the power supplied and the product calculated from. Here, however, the height is only the actual pump head - well, this is then also at the water turbine the case.
In a few hydropower plants, the rotation of the turbine is transferred to a generator via a gearbox. Thus come to the losses of the turbine could be added the losses through the transmission and it is calculated as the mechanical power as follows:
Furthermore, the generator does not have losses. The ultimately generated electrical output of the turbine is calculated from:
From the equations it will be seen that a large height of fall can compensate for a low water flow, and vice versa. This means that the relatively small amount of water of a mountain stream with high head can produce more electrical energy than the large amount of water of a river that is only overcome by the difference in height of a weir under certain circumstances.
Constructive details
In order to achieve optimal efficiency, the turbine must be adapted to the different drop heights and water flow rates. A storage power station in the mountains therefore need a different turbine as a hydroelectric power plant on a river.
Water turbines are running with outputs of 200 watts up to a thousand megawatts. The turbines of the power plants are individually designed and made before they are finally assembled at the construction site of the power plant. The wheels of such turbines have a diameter of up to 11 m. However, water turbines can not miniaturize any, since small turbines a similar effort for the regulation have such large turbines and are particularly sensitive to water pollution.
A special feature of the water turbine is the complex control their speed with the ever slightly fluctuating flow of water. The regulators keep running with hydraulically operated actuators ( valves and vanes ) the speed constant and secure the turbine also against " runaway" if the torque on the generator shaft should drop for example because of an empty barrel.
On a speed control can be dispensed with in small turbines in network operation, since the generator is maintained at grid feed due to the mains frequency at a constant speed. If the power fails but then the water supply must be interrupted in order to prevent runaway when the turbine and the generator was not designed for the idling speed by means of valves or contactors. Normally this is about twice the half times to operating speed.
The proportion of turbine and governor of the total investment of a hydroelectric power plant is considerable. This cost share is in small systems up to 50%, in large plants 10 to 20 %. Water turbines feature the other by a long service life, in many power plant are machines since the end of World War I in use. They count in this case to the technical monuments which are still in operation.
History of Technology
The techno-historical predecessor of water turbines were water wheels with vertically disposed shaft, which came into use in the 18th and 19th centuries. The name comes from Claude Burdin turbine (1790-1873), who called in 1824 his invention so. 1826 had the French Société d' encouragement in Paris at a price of 6000 French franc to the manufacture of turbines advertised. The first applications were fruitless, until it until 1833 the French engineer Benoît Fourneyron succeeded, the price to purchase the turbine, named after him, the theory of which was determined in 1838 by Jean -Victor Poncelet.
The Fourneyron turbine operates similarly to her later following Francis turbine, except that the vanes have a fixed position and run the water in the reverse order from the inside to the outer wheel. The design was well suited for uniform water inflows and sat down within a few years against the undershot waterwheel by. With optimum water flow, the turbine had an efficiency of up to 85%. It is no longer manufactured, despite its simple construction today. In order to adapt the Fourneyron turbine to the available process water, the outer blades along a movable cover was attached to the inside, with the help of the water flow was changed.
The Fourneyron turbine has been improved several times:
Turbine types
Constant-pressure turbines
The water pressure does not change during the flow through the turbine. It is transmitted to the impeller only kinetic energy. Turbines of this type are the Pelton turbine and the cross-flow turbine.
Reaction turbines
The pressure of the water entering the same and takes up to the exit from steady. It is therefore the potential and kinetic energy transmitted to the impeller. This applies to the Francis turbine and the Kaplan turbine.
Survey
In addition:
- Wells turbine for large amounts of water with periodically changing the direction of flow for use in the wave power plant
- Hamann turbine for low flow rates of the watercourse for individual use