Investigations on the Influences of Winding Positions and Rise Times on the Winding Isolation System within the Line-End Coil under Fast Rising Impulse Voltages

The steep-edged voltage impulses from new wide bandgap power electronic devices shorten the lifespan of the motor isolation system significantly because of the highly uneven distributed voltage, especially in the line-end coil. This distribution leads to a much higher transient local field strength in the winding, which accelerates the aging process and reduces the isolation strength of the insulation materials. As a result of that partial discharges occur at early stage. Thus, a method for the reduction of the high local field strength is necessary and vital for the lifetime extension of the electrical machines fed by steep-fronted PWM (Pulse Width Modulation) voltage waves. In this study, a genetic algorithm is utilized to investigate the possible worst and best cases of electrical field distributions based on the real spatial locations of stator windings in the slots. Effects of each case are presented and discussed.