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ISSN Imprimir: 1093-3611
ISSN On-line: 1940-4360
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ANALYSIS OF THE SPONTANEOUS OSCILLATIONS OF THE VOLTAGE OF AN ARC BURNING ON HETEROGENEOUS ELECTRODES BY CURRENT INJECTION
RESUMO
It has been shown that large amplitude voltage oscillations may be present in free burning arcs in special conditions. These conditions concern the cathode nature, the ambient gas, the gap length, the arc current. To investigate the origin of these oscillations, we inject in an oscillating arc a stepwise current pulse, and record the induced arc voltage variations Depending on the sign of the injected current ΔI vs. arc current I, and on the relative time position of the current injection vs. voltage level, we observe either stable arc behaviour, with a voltage variation proportional to the injected current : ΔU = ui ΔI/I, where ui is the voltage drop in the plasma, or sensitive unstable levels where the voltage exhibits anomalous large amplitude variations. In this latter case, with ΔI > 0, the arc voltage shifts towards the higher level for a short period, then rapidly falls to the lower level. For the stable arc case, we compute the minimum arc voltage and the arc impedance.