Insights into the Definition of Converter Surge Rise Time and its Influence on Turn/Turn Electrical Stress

Electrical converter-cable-machine systems, such as those in renewable source interfaces and transport drives, are operated with increasingly fast and high-performance converters. Their effects on the stator insulation and, in particular, on the turn insulation, need be understood in detail. A dynamic/FEM model is used to simulate the maximum voltages stressing the turn-to-turn and phase-to-ground insulation. The results show the role of rise time in the generation of overshoots and uneven voltage distribution. For machine to be fed with wide-bandgap converters, the limitations of PD testing using conventional surge generators are highlighted. Besides, the limits of the rise time definition and its role in the IEC60034-18-41/42 standards are discussed with reference to non-ideal waveforms acquired from a SiC bipolar converter.