Investigations of modified nonlinear electrical materials for end corona protection in large rotating machines

Materials with nonlinear dielectric behavior are applied in rotating electrical machines for a defined control of the electrical field strength in the insulation system of stator end windings. To achieve better control of the electrical parameters a new filler material has been developed. Due to platelet shapes and coating with oxide layers the electrical behavior indicates a minimized spreading. The electrical resistance could be adjusted by different doping conditions of the oxide layers. Nevertheless, operational and environmental influences are not sufficiently investigated for operational application. In this paper the combined electrical, thermal and chemical properties under direct voltage stresses are worked out.