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Partial Discharge (PD) measurements output,\ud when non-sinusoidal voltages are applied to insulating\ud systems, can have different meanings, depending on the\ud voltage waveform frequency content and on the PD\ud probe circuit. A PD detection circuit is designed for a\ud low noise-to-signal ratio, thus for suppression of the\ud residual high frequency (HF) voltage. Such a\ud suppression varies with the applied voltage rise time: for\ud fast rise rate voltage pulses the PD measurements\ud deserve a specific study. When multiple PD sites are\ud active in the same insulation system and when they give\ud rise to PD inception during the voltage rise/fall, effects\ud due to the signal superimposition should be considered.\ud During quasi-square wave PD tests on twisted pairs the\ud voltage rise rates, the voltage test levels and the high PD\ud repetition rate during voltage "pulses" have been\ud suitably inter-played, taking in account analogue and\ud digital PD acquisition systems, in order to evidence the\ud PD measurements actual information content. The\ud obtained results evidenced the limits of high and low\ud frequency PD measurements; in certain instances they\ud did negate both the validity of the relation and the possibility of\ud resolving each single PD pulse

Nowadays electrical motors used in industry applications are usually coupled with inverter drives so that the stator motor windings are subjected to severe voltage waveforms such as PWM. When electrical motors having stator windings realized by means of type I random wire wound are subjected to these kinds of voltage waveforms, reliability problems due to degradation phenomena increase. In this research work different insulating nanocomposite enamels have been analyzed: suitable twisted pair specimens insulated by the studied enamels have been prepared and tested. Breakdown voltage tests and electrical aging tests have been performed: during the electrical aging tests the specimens have been subjected to pulsed voltage waveforms having amplitude higher than the partial discharges inception voltage level in order to operate in presence of partial discharges. Enamel breakdown condition has been chosen as end-point criterion and both the relevant voltage breakdown and life time values have been collected and compared. Analyzing the obtained results it has been possible to point out the behavior of the different insulating organic enamels when subjected to electrical degradation phenomena.

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