Spiral turbine
A spiral turbine , also known as a closed turbine , is a water turbine that is provided with an inlet spiral. The contrast to this is the shaft turbine , also known as an open turbine or chamber turbine , in which the water is not specially guided before it enters the guide vane ring. Spiral turbines are the usual design for Francis and Kaplan turbines today . Compared to shaft turbines, they are more efficient. Nowadays, shaft turbines are usually only found in historic power plants and small hydropower plants with low heads.
history
The Francis turbine developed in 1849 was initially designed as a shaft turbine. This simple construction could only be used for drop heights of up to 5 meters. In Germany, Georg A. Pfarr added the inlet spiral to the Francis turbine so that greater heads could also be used.
technology
Inlet spiral
The inlet spiral ensures that the water receives an additional swirl even before it hits the guide vane ring and that it hits the guide vane ring at the same speed over the entire circumference of the turbine. The inlet spiral has the shape of a single-flight screw, the diameter of which decreases towards the inside. This ensures that the same pressure and the same speed can be maintained over the entire circumference of the turbine, although the volume flow through the water flowing into the turbine is getting smaller and smaller from the inlet nozzle of the inlet spiral to its end. The water enters the guide vane ring through a gap on the inside of the screw.
Inlet spirals for large heads are made of cast steel or welded constructions. At low heads, especially with Kaplan turbines, the inlet spiral is usually made of concrete . For structural reasons, the lip of the gap on the inside of the inlet spiral connects to a truss ring, which consists of two truss ring decks that are connected with trusses. These cross members are designed as stationary guide vanes in front of the guide vane ring. Large volute casings must be made in multiple parts that are manageable and transportable. They are only put together on the construction site.
Inlet spiral of a horizontal Francis turbine
in the Rabenauer Grund power plant
Multi-part volute casing of a vertical Francis turbine built in the 1940s,
Grand Coulee Dam , USA
Shaft turbine
In shaft turbines, the turbine is housed in a simple rectangular turbine chamber. The water runs directly into the guide vane ring without additional guidance. The linkage for adjusting the guide vanes is open in the headwater. Turbulence of the upstream water in the corners of the turbine chamber and uneven flow to the turbine circumference lead to efficiency losses.
Francis shaft turbine
Standing Francis shaft turbine by G. Luther from Braunschweig, approx. 1907
Kaplan shaft turbine in the Swedish power station Skogsforsen, 1939
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Individual evidence
- ↑ a b Francis turbine. Kraftwerk Reinisch GmbH
- ↑ Deutsches Museum: Francis spiral turbine, 1886. .
- ↑ Patent WO2012110197 : Hydraulic flow machine . Registered on January 31, 2012 , applicant: Voith , inventor: Martin Schabasser.
- ↑ Patent US1462890 : Spiral Casing. Registered on April 30, 1920 , inventor: HB Taylor.
- ↑ M. Adolph: Turbo machines : Turbines, centrifugal pumps and compressors An introduction . Springer-Verlag, 1965, ISBN 978-3-642-88294-4 , p. 109 ( google.cz ).