Square-Shaped Waveform Pulse Control to Minimize PD Exposure Within Motor Insulation

Pulsewidth modulated (PWM) voltage supply is important for efficiently controlling the performance of electric motors. The downside brought up by its use is that the electric stress imposed on motor insulation considerably increases, compared to traditional 50- or 60-Hz sinusoidal supply, and it often results in the reduction of insulation lifetime. In this article, the advantages arising from employing PWM waveforms with adjustable rise time and pulse height are verified by evaluating their influence on partial discharge (PD) characteristics of motor winding insulation, exemplified using twisted pair test object. A test setup enabling control of the voltage pulse shape is introduced for demonstrating that the intensity of PD activity can be reduced or even ceased by adjusting the slope of voltage flanks at which the electric stress reaches its maximum level, including application of ultrashort rise times imposed by modern semiconductor technology. It is also shown that the proposed solution yields reduced PD activity without increasing switching losses and the influence of reflections becomes considerably limited. Quantitative guideline to reduce the PD activity is presented.