Effects of oscillating waveforms on surge voltage endurance

Although voltage endurance is usually viewed in terms of a power frequency test, the increasing use of power electronics has highlighted the awareness of the loss of insulation life due to the application of repetitive surges. An experimental study is reported to quantify the voltage endurance of bisphenol A electrical casting resin when subjected to oscillating impulse voltages in a divergent electric field. Surge voltage endurance has been quantified as a function of pulse width (0.05 μs-100 μs), repetition rate (30 Hz-1 kHz), and polarity. The results suggest, at least for positive polarity impulses, that estimates of endurance under surge conditions can be made from conventional power frequency data provided that the appropriate corrections are made to the conventional voltage endurance curves. A theoretical treatment is provided to allow this correction to be estimated based on a consideration of the life removed by the multiple application of a damped train of impulses