Temperature and electric field dependence of stress grading on form-wound motor coils

The paper addresses the temperature and electric field dependence on the conductivity of the conductive armor and stress grading tapes on form-wound motor coils. The temperature and electric field dependence is measured in the laboratory, and the nonlinear dependency is used in transient FEM simulations of the potential distribution on the form-wound coils. The surface potential distribution, for various temperatures and applied voltages, is measured in the laboratory from which the surface electric stress is calculated. Good agreement between the simulated and measured stresses is obtained. A temperature of 155 °C is shown to have little influence on the stress grading, but the electric stress dependence on conductivity is shown to have a major influence on the stress grading of the motor coil examined in this study.