Insulation performance under switched voltage waveforms

The increasing use of IGBT-controlled pulse width modulated voltage waveforms for motor power supplies has prompted many studies to evaluate their impact upon insulation system performance. The works described in this paper indicate that when voltage waveforms contain significant harmonics at frequencies close to the relaxation peak for the insulation, failure arising from surface charge accumulation can occur. Ageing by partial discharges will take place when the voltage is above the discharge inception level and this level may change according to the duty cycle of individual carrier periods. If operating conditions do not promote either of these mechanisms, failure will occur through normal thermal degradation