Electrical aging tests on different kind of insulating systems adopted for induction stator motor

The massive adoption of electronic converters to supply induction motors leads to critical problems during the normal operation. One of the most investigated problem is the unexpected early failure of the stator winding insulation. When the motors are supplied by electronic converters, the stator insulating system could be subjected to over-voltages due to resonance and reflection phenomena; if these over-voltages exceed the partial discharge inception voltage, partial discharge activity can incept. The erosion of the enamel used to insulate the stator winding wires, due to the presence of partial discharge activity, leads to the degradation of the dielectric characteristics of the insulating system and in the worst cases, to a total breakdown. This investigation campaign presents the outcome of experimental tests aimed at the investigation of the unipolar pulses voltage waveforms role on the degradation of Type I stator winding insulation systems. Induction motors having different insulating systems have been considered. The stator windings have been realized using conventional or corona resistant enameled wires.