Off line measurements of partial discharges in turn insulation of low voltage rotating machines

Premature failures of low voltage rotating machines fed by inverters are often attributed to the existence of Partial Discharges (PD). Nevertheless, a clear and direct evidence of PD existence in such systems is far from being established. Since their location is not in the turn to ground or phase to phase insulating materials, classical ac tests are not applicable. We present in the following an off line test able to solve this problem.