Computational Approach to Electrical and Thermal behavior at End-turn Stress Grading System of Inverter-fed Rotating Machine under PWM Waveform

Abstract

SiC-based nonlinear conductive stress grading tape (SGT) has been used at an end-turn stress grading system of a form-wound rotating machine. Although previous researches reported that high-frequency repetitive pulses cause electric field enhancement and local heating at the SG system, few paper deals with the detailed electrical and thermal behaviors under pulse width modulation (PWM) waveforms, which contain not only the repetitive high-frequency, i.e., the carrier frequency, component but also the fundamental frequency component. In this study, the surface potential, the electric field, the time-averaged power densities as well as the resulting temperature rise under the 3-level PWM waveforms were investigated by the transient electric field and thermal coupled FEM simulation. Furthermore, the behavior of the accumulated charges within the SGT was analyzed, based on the simulation results. Consequently, it has been revealed that the charge behavior and the power densities by the carrier-frequency component and those by the fundamental frequency component could be separated individually.