Models for degradation of self-healing capacitors operating under voltage distortion and temperature

Nowadays the increase of polluting loads in electrical networks affects supply voltage sinusoidality more significantly than in the past. Voltage distortion can decrease reliability of electrical devices, that is, increase their failure rate. This paper deals with the effect on aging acceleration due to harmonics for a simple insulation system, i.e. low-voltage self-healing capacitors. The most stressing features of the nonsinusoidal voltage and current waveforms (peak value, rms value, slope, etc.), as well as temperature, are investigated in order to single out the extent of their effect on life reduction. For this purpose, life tests under temperature and voltage distortion were carried out considering different kinds of harmonics, summed to fundamental one, able to vary peak and slope of the voltage waveform. The tests were performed both at room and at high temperatures. The results, statistically processed through Design of Experiment (DOE) techniques, show that the effect of temperature on ageing is significant, but the most important effect is that relevant to peak voltage. A life model involving all the main stressing factors (peak voltage, rms value and slope, as well as temperature) is therefore proposed