Life tests on twisted pairs subjected to PWM-like voltages

This investigation regards the partial discharges (PD) ageing processes of motor winding insulation (enamelled wires) subjected to "fast rising and dropping" voltages, i.e. to a PWM controlled inverter drive voltage waveform. Twisted pair specimens were fed till failure by two different PWM like (and by a sinusoidal) voltages, at several voltage amplitudes, in presence of PD. The relevant life curves were traced and the PD were measured. The outcome evidenced that the life curves besides depending on the Vpp voltages they evidence a very strong connection with the relevant waveforms.