Behaviour of Conventional and Nanofilled Impregnation Resins when Subjected to PD Activity

The insulating system of stator windings of rotating electrical machines are usually based upon organic enamel as primary insulation and impregnating resin used for the secondary insulation. When the motors are supplied by power electronic converters, the stator insulation system is subjected to voltage waveforms such as PWM composed by trains of pulses. Due to reflection phenomena, overvoltage can be associated to pulsed waveforms and partial discharge (PD) activity can incepts leading to the insulating system failure in short time. In this work different types of secondary insulating materials, consisting of conventional or nanofilled impregnating resins, have been compared. Suitable twisted pair samples prepared by means of wires insulated with conventional enamel and by different impregnating resins have been tested. The twisted pair samples have been subjected to sinusoidal voltage waveforms, having amplitudes higher than the Partial Discharge Inception Voltage. Aging tests have been performed, monitoring the PD activity until the total breakdown, which is assumed as end-point criterion.