Sammendrag
In Norway, prototype efficiency measurements are mostly carried out by the thermodynamic method. For low head turbines, the pressure-time method can be most accurate and the cheapest way to perform efficiency measurements. The pressure-time method is not very well known by the Norwegian consultants and hydropower plant owners and therefore not often used. The experience data from Norwegian power plants measured by the pressure-time method is scarce, and the uncertainty of the measurements is often a question mark.
The paper will present uncertainty from efficiency measurements carried out at Svean Power Plant which is located near Trondheim, Norway. Here, both pressure-time and thermodynamic efficiency measurements has been carried out during the autumn 2005 by students and staff from the Waterpower Laboratory at The Norwegian University of Science and Technology (NTNU). The results from the measurements are presented in a paper written by Dahlhaug 2006.
Svean Power Plant has installed 3 Francis manufactured by Kværner Bruk and made in 1940 – 1948, where the head is 50 meter and the nominal power output from each turbine is 11 MW. The pressure shaft has a 27 degree slope, it is about 110 meter long, it has a steel riveted lining in its whole length and the diameter is 3.18 meter. The speed number, of the turbines are 0.9 and the speed is 300 rpm. The turbines are of the twin-Francis type. This means they have two runners back to back, two draft tube bend and one spiral casing. The outlet of the draft tube is one cross section with the flow rate from both draft tube bends.
The paper shows all of the equations and details for the determination of the uncertainty of a pressure-time efficiency measurement.
The uncertainties are calculated to numerical values taken from the Svean Power Plant measurement without further explanation or references, as we think that it is important to get a feeling of the magnitude of the uncertainties without making this paper too complicated.
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