dV/dt Impact on Turn-to-Turn Overvoltage Distribution in Motor Windings

Cable connected motor winding insulation is prone to failures owing to standing wave overvoltages (OV), caused by switching transition dV/dt. Standing wave is impacted by the motor drive system differential mode and common mode impedance interactions, as well as excitation frequency dV/dt. Winding and cable impedance create a complex combination of resonances and antiresonances. Wide band gap power electronics generate high dV/dt that exacerbates the OV phenomenon. According to the literature, the overvoltage across the motor winding is not distributed evenly between the turns. First turns are reported to be under higher overvoltage where OV is lower and more similar for the subsequent turns. However, in this paper with the accurate HF modeling of the motor drive system, the overvoltage distribution across the turn-to-turn (TT) of the motor winding for different dV/dt is investigated. It is proved that the voltage distribution trend does not remain constant. First, it is due to the different resonances across different TT in an unsymmetric network of drive system. Second, according to the trapezoidal waveform, different dV/dt excitation introduces different bandwidth of the secondary harmonics contributed to the OVs. So, not always the first turn is under highest voltage. Not clear understanding of the OVs could cause insulation overdesign for the first turns or easier degradation of the lateral turns. In this regard, this paper gives a guideline to study the system in regards of impedance interactions with excitation dV/dt in the WBG applications. Therefore, based on this study the appropriate insulation or filtering design to alleviate the OVs can be decided. The ground truth experimental validation for high frequency modeling of the system under test is provided.