Performance of cables and machines insulation at various parameters of impulse stimulus

The impulse stimulus like PWM (Pulse Width Modulation) creates special challenges on the requirements of the insulation systems of both electrical machines and cables. Voltage waveforms characterized by repetitive slopes of fast rise- and fall times are influencing the aging phenomena in the insulation system of cables and motors, especially creating the danger of partial discharge (PD) development. The repetitive character of the pulses (usually in kHz range) combined with rapid voltage changes results in dedicated aging processes. This problem has been investigated in the laboratory setup, on samples of polymer cable and machine insulation. The dedicated measuring system allowed for setup of various parameters of IGBT based inverter like rise time, frequency, voltage, du/dt, polarity. The PD patterns have been acquired both at the slope and on the pulse constant part. The comparative assessment shows influence of the du/dt steepness and switching frequency on the PD activity on the waveform slopes but also on the plateau part. The qualitative illustration of these parameters on PD inception and magnitude has been presented.