Analytical approach of PD activity in low voltage motors fed by inverters [adjustable speed drives]

Adjustable Speed Drives are very efficient and convenient. However, pulse width modulation generates steep fronts which impose on the motors, through cable reflection overvoltages. This phenomenon should generate partial discharge activity within the stator insulation. The main goal of the present study is to quantify parameters and mechanisms which control PD ignition in order to define threshold voltages above which their activity can be ascertained. Moreover, turn-to-turn, phase-to-ground and phase-to-phase insulations present quite different characteristics and withstand very different voltage stresses. The study determines which kinds of insulation are the most susceptible for PD activity. Calculation results are presented and discussed.