Partial discharge activities in transformer insulation under steep front voltages

Gassing problems and premature insulation failures of wind turbine transformers have been documented lately, indicating concerns with insulation reliability of power electronic converter-fed devices. This fact shows that the transformer insulation system degrades under high dV/dt voltages generated in wind energy plants at a faster rate than those operated under power frequency AC voltages of the same amplitude. To study such degradation processes, unlike the cases of AC or DC voltages, under high dV/dt voltages, interferences coming from the pulse generator and fast oscillatory input voltages pose substantial challenges. In this work, a method to evaluate the effect of voltage waveform characteristics such as rate of rise (ROR) on the extent of partial discharge activities, based on the changes in hydrogen content in the transformer oil/paper insulation system is investigated.