Influence of the rise time and of the temperature on the PD inception voltage of enameled wires

This work describes an investigation about the influence of two service parameter on the PD inception voltage threshold of type I random wire wound stator insulation; the temperature and the voltage gradient (i.e. the rise time). An experimental campaign of PD inception tests was carried out on twisted pair specimens applying unipolar voltage pulses having different rise time. The results have been compared to PDIV measurement obtained applying to twisted pairs other voltage waveforms: sinusoidal voltage and voltage waveforms reproducing the output of a PWM switching drive with or without superimposed surges. The outcome evidences some interesting trend of the inception voltage with the voltage gradient and the test temperature that could be usefully used in order to relate test conditions to actual operating conditions of random wire wound motors.