Influences of Contact opening speeds in the range of 0.5 to 200 mm/s on break arc behaviors of AgSnO2 contacts in DC conditions

Break operations of DC inductive (L=20mH) currents in the range from about 1 to 10A at 14V were conducted with AgSnO2 contact pairs under different contact opening speeds from 0.5 to 200mm/s in air. Break arc voltage waveforms were observed, and total break arc durations and metallic phase arc durations were measured. After the experiments, averages for the total arc duration and the metallic phase arc duration were calculated at each condition. With load current of about 3A or more, the average total break arc durations showed shortening tendencies with increases in the contact opening speeds, but only in the middle range of the tested speed levels. With slower and faster speed levels, the arc shortening tendencies became less significant. Even in the middle speed range, the average total break arc durations were not in inverse proportion to the contact opening speeds. However, the metallic phase arc duration characteristics were found to show inversely proportional relationships with the contact opening speeds under certain operating conditions. Thus, the contact opening speeds exhibit clear influences mainly on metallic phases of break arc discharges. It seems the inductive component in the load circuit provided a contact gap with sufficient energy to prevent quick arc extinctions. Further experiments were also done in a DC resistive load circuit for comparison.