Electrical and thermal computation of stress grading system in inverter-driven medium voltage motors

This paper focuses on analyzing the electric field and the temperature distribution in a typical stress grading system used in medium voltage rotating machines under pulse width modulation voltage source conditions. Two analysis models for electric field and heat transfer processes are developed to take into account the nonlinear relationship between the electric field and the electrical conductivity of Silicon Carbide (SiC) semi-conductive tape. The simulation results give a fundamental background to explain the failure of the stress grading system in inverter-driven medium voltage motors.