Analysis of DC and AC arcs at break with spectrum analyser

The frequency components of the arc voltage waveform for alternating and direct currents ranging from 5-15 A and a gap-length of 0.1-1.0 mm for a resistive circuit are measured with a spectrum analyser. Measurements reveal that the arc voltage for alternating current is composed of odd harmonics of the supply frequency. The amplitude of frequency components for direct current are much smaller than for alternating current for the same test conditions. A detailed comparison of a pair of AgCdO contacts with the case of opposing AgCdO and AgCuNi contacts for a direct current test suggests that the use of the latter reduces the number of frequency components and also that these extend to higher amplitudes. This paper also proposes that frequency components could be used for condition monitoring of switchgears and erosion prediction of power switching devices.