Investigation of Control Methods for Local Heating at End-turn Stress Grading System of Inverter-fed Rotating Machines

Abstract

SiC-based nonlinear resistive materials and carbon-based semi-conductive materials (corona armor tape or CAT) are used at end-turn stress grading systems of high voltage rotating machines. Recent studies show that local heating as well as electric field along the system become problematic under PWM and high frequency repetitive pulses waveforms. Potential distribution, power dissipation and resulting temperature rise under the repetitive pulses are calculated based on three dimensional transient electric field and thermal coupled FEM computation. Computational results of surface temperature as a function of CAT conductivity have shown reasonable agreement with the experimental ones and we have validated those computations. In addition, the appropriate CAT conductivity for suppressing both local heating and electric field are evaluated based on the above computational results.