Stator end-winding currents in frequency-domain dielectric response measurements

This is a study of the components of capacitance, loss and harmonic currents that the nonlinear ´corona protection´ coating used on stator end-windings adds to frequency-domain dielectric measurements. The work is based on measurements on simple laboratory models, compared to one-dimensional numerical models having discrete or continuous parameters and linear or nonlinear resistance. The necessary components and parameters of the numerical models are discussed by comparison with the measurements. Commonly used models of the conductivity of the SiC-based nonlinear material are compared to dc measurements on samples. The studied range of the applied voltage has amplitudes from low values up to the levels of operation and testing of stator windings, and frequency from line-frequency down to millihertz.