RF Currents Produced from AC Arcs with Asymmetrical Electrodes

The RF current (0-20MHz) produced by an air arc with asymmetrical (graphite-copper) electrodes was investigated for 120Vac 60Hz over a current range of 1.2A_rms to 45A_rms. Time resolved spectral signatures of measured RF currents showed amplitude dependence on 60 Hz arc current level, voltage polarity, electrode material, and circuit impedance. For most conditions, RF currents were measured only when the copper electrode was the cathode. It was hypothesized that the formation and extinction of cathode spots was likely the primary source for the measured RF current with a low level contribution from ion oscillations. A model was proposed that showed how graphite, transferred to the copper electrode, could create RF currents leading to the asymmetrical behavior. Circuit impedance, over the frequency range of interest, was also shown to affect the measured RF current amplitude. This work is useful to those who want to gain an understanding into the behavior of RF currents generated from series arcs at 120Vac in typical NM-B residential distribution wiring.