Analysis of two plane electromechanical model of shape deviation in a hydropower generator

Hydroelectric power supplies about 20 percent of the world's electricity and is the most important renewable energy converting industry. Swedish hydropower plants produce between 55-74TWh a year. These plants where built thirty to one hundred years ago and where constructed for base load. With new developments in energy production, for instance nuclear and renewable power, many hydropower plants have a new task, namely to function as regulators and keep frequency in the power net constant. Which means that constructions that where not built for it will have to do many starts and stops in their lifetime. This makes it interesting to examine the rotordynamic effects in hydropower generators. All generators have shape deviations since it is not possible to manufacture perfect circular generators. Especially in Hydropower applications, where the diameter is normally large and the relative airgap is small. These properties make it likely that the response of the system depends on the shape deviation. This thesis examines the effect shape deviation of the generator has on the response. It compares the difference between using the mean shape deviation on rotor and stator compared to two shape deviation one on the upper half of the rotor and stator and one the lower half. With two shape deviations there will be a bending moment due to the differences in shape of the upper and lower parts of the generator. The main goal is to investigate the effects of these bending moments and also to use a real generator as a model(Krångfors G2 at River Skellefte älv). The results show that two shape deviations give rice to bending moments in new frequencies. There is only a very small effect on displacement response of the rotor. The new moments are seen in the angular response, where there is a clear difference between the two cases. In the case of Krångfors G2 it was found that the stiffness of the rotor was high and therefore only the first frequency of the shape deviations is likely affect the system. But, in other hydropower generators it is possible that the bending moments can affect the dynamics of the system. Then the methods presented in this thesis can be a valuable tool.Validerat; 20101217 (root