PDIV and RPDIV on different temperatures on different kind of type I insulating system

Nowadays the massive adoption of electronic converters to supply electrical motors leads to critical problems during the normal operation. In fact when the motors are supplied by electronic converters, the stator insulating system could be subjected to over voltages due to reflection and resonance phenomena. Frequently this over voltages exceed the partial discharge inception voltage and partial discharge activity incepts. The presence of partial discharge activity implies the degradation of the dielectric characteristics of the type I insulating system and in the short-medium time, leads to a total breakdown discharge. Three different types of type I insulating system used in rotating electrical machines fed from inverters have been considered and studied. The PDIV and RPDIV at different temperatures have been measured and compared. During this research study the stators of asyncronous motors have been subjected to sinusoidal waveform and unipolar positive voltage pulses at different temperatures. In order to perform the RPDIV measurements a modified surge tester has been used so to apply unipolar positive voltage pulses at the terminals of the windings. The correlation between the repetitive partial discharge inception voltage and the partial discharges inception voltage measured at different temperatures has been studied.