Challenges to machine windings used in electrical generators in wave and tidal power plants

The majority of electrical generators in wave and tidal power plants are face harsh environmental conditions. Particularly the seals between the moving shaft and the stationary generator as these are mechanically stressed under pressure of the sea water. Flooding the electrical generator and the air gap respectively is a possible solution that would overcome seal failure. With this proposal, the strains on the seals can be reduced as they would have to seal non-moving parts against the sea water only. The lifetime of seals could be prolonged with this measure. On the other hand, this will also result in changes to the electrical behavior of the windings and the electrical machine respectively. This is the subject of this paper. Mainly, these are changes to the winding capacitances. They result in a different transient behavior, for example when the machine is operated with switched inverters. The performance of six different insulation materials for the submersion in sea water are studied and the results are compared to the standard operation in air. Furthermore, with the changed sealing methods the thermal characteristics are altered, which will be also analyzed within this work.