At current interruption by electric contact, a repetition phenomenon of arc extinction and re-ignition is often observed before complete extinction of arc discharge, in some cases for a long time and in other cases for a short time. Occasionally, no re-ignition is observed. From a viewpoint of arc duration, the period of this repeating arc is also an important factor, if it is very long. However, the conventional explanation about the contact arc duration excludes this repeating arc phenomenon so that it fails to explain the reason and the duration of this phenomenon. For the purpose of investigating why this phenomenon occurs and how long it lasts, the arc extinction current and the arc re-ignition voltage have been measured for tungsten electrode, palladium electrode, copper electrode, and silver electrode. The circuit is, for simplicity, resistive with a capacitor source voltage and a fixed short arc gap of 0.5 mm. Taking newly into account the idea of unstable arc region by the measured results, the conventional explanation was improved. As a result, the reason and the duration of arc extinction and re-ignition phenomenon have become understandable. For simplification, the main description is based on the results by tungsten electrode. The results by other electrodes are summarized in appendix.

This paper proposed the method as an estimation on the size of discharge spots through observation on traces after the discharge arose in circumstances gases mixed hydrocarbon gas. Namely, the circular carbonaceous deposit and the carbonaceous heap are observed on cathode and anode surface, respectively, after the short gap discharge arises in N2+NO+CH4 gases. The current density, which is the normal conversion current density, is calculated from the size of the trace of discharge and its value is about 1.010-9 A/(cm2 Pa2) in case that the concentration of CH4 is 0.6%. The value is about 1/5 of values that are reported in the former articles and is reasonable one.