The voltage stresses of insulation systems under PWM inverter supplies

Exploitation stresses are causing degradation of high voltage insulation systems. The assessment of intensity and dynamics of these processes, being a consequence of local, working electric field strength is considered mainly at the sinusoidal voltage. However in applications where power electronics converters are used the voltage stress has usually a form of fast switching pulses composed of repetitive sequences. Such pulse trains pose usually a modulated width and fast rise-and fall-times. Such conditions have essential influence on inception and development of partial discharges in insulating systems subjected to non-sinusoidal stimulus. The insulation degradation mechanism is especially important for cables and electrical machines subjected to non-sinusoidal waveforms. A novel time-resolved partial discharge (PD) surge pulse acquisition has been described. The method is based on very fast PD registration during repetition of HV surge pulses on insulating material and visualization if form of PRPD like pattern. Comparison between PD patterns obtained at surge pulse and subjected to power frequency sine and trapezoidal is shown.