Arc Movement Investigations of Break Arcs of AgSnO2 Contacts under Applied External Magnetic Field in Inductive DC Load Conditions

Break operations of AgSnO
₂
contact pairs were conducted in a DC inductive (L=5.7mH) load circuit with 14V-7A, 14V-12A, 20V-7A and 20V-17A at different contact opening speeds from 1 to 200 mm/s and with/without external magnetic field application of about 120 mT in air. Break arc movements were observed with a high-speed camera, and arc voltage/current waveforms were also obtained. In some conditions especially with smaller load current levels and slower contact opening speeds, magnetic blowing were not observed even with applied external magnetic field. However, in such cases, certain reductions in break arc durations were still observed. When magnetic blowing was observed, arc movement started almost at the maximum level of the calculated Lorentz force. When magnetic blowing was not observed, the calculated Lorentz force levels were found to follow the same trace up to the maximum level as the blown cases. Thus, some factors other than the Lorentz force level seem to have critical influences on realization of magnetic blowing. In the non-blowing cases, arc was found to move in the direction opposite to the Lorentz force direction. When the magnetic field in the opposite direction was applied, the arc movement direction was also switched in the opposite direction. Mechanism for explaining such arc movements has not yet become clear.