Suppression of Local Heating on a Silicon Carbide Layer by Means of Divided Potentials

A new method was investigated for suppression of local heating of a silicon carbide layer used for field grading on stator coil ends in HV rotating machines. By means of synchronous divided potentials at proper positions on a SiC layer, surface current bypasses through the electrodes of the divided potentials, which prevents thermal runaway of the SiC layer during ac dielectric strength tests of coil insulation. Since SiC shows highly nonlinear resistivity, approximate formulas of heat distributions are discussed in detail on the assumption of ideal nonlinear resistivity. The formulas are compared with the results of numerical calculation and experiments.