Searching for the factors which affect self-healing capacitor degradation under non-sinusoidal voltage

The purpose of this paper is to show how voltage distortion may cause accelerated aging of insulation systems, particularly of self-healing capacitors. Distortion is due to the presence, in the supply voltage waveform, of harmonics which are typically detected in distribution ac networks. These harmonics sum up to the fundamental component giving rise to voltage waveforms which can considerably differ, for peak value and shape, from the sinusoidal waveform. The results of life tests carried out on capacitors subjected to non-sinusoidal voltage allow an investigation on the most significant factors which affect endurance to be performed, resorting to appropriate statistical techniques. Voltage peak seems to be the most significant factor for aging acceleration, but also waveshape and rms voltage play a significant role. A life model is thus derived, which provides a relationship between failure time, defined as the time required to reach a given decrease of capacitance, and appropriate figures derived from the voltage waveform. These figures take into account, in fact, voltage peak, waveshape and rms.