Inverter-fed drives: which motor stators are at risk?

This article describes measurements of the surge voltage characteristics from a number of motors driven by inverter-fed drives (IFDs). The measurements were done with both laboratory and purpose-built instrumentation. Further, we discuss why certain surges deteriorate the insulation, and we give guidelines for determining which motors may be at risk of failure from IFD voltage surges. The effect of these surges on stator windings is also included, as well as means to determine if a motor installed in a severe surge environment will fail.