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

Abstract: 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.