1-2hit |
Seika TOKUMITSU Makoto HASEGAWA
When AgSnO2 contacts were operated to break an inductive DC load current of 14V-12A, 20V-7A or 20V-17A at a contact opening speed of 10mm/sec or slower, application of an external magnetic field resulted in reductions in break arc durations even without magnetic blowing. Simple estimation of Lorentz force to be applied onto arc column revealed that a certain minimum magnitude of Lorentz force seems to be required for initiating arc blowing. Certain relationships between the Lorentz force magnitude and the timing of metallic-to-gaseous phase transition were also found to exist.
Break operations of DC inductive (L=20mH) load currents up to about 5A with 14V were conducted in air with AgSnO2 contact pairs under different contact opening speeds, first up to 20mm/s and then to 200mm/s. Average break arc duration at each current level was calculated under the respective opening speeds. While break arc durations became shorter with increases in the opening speeds at larger current levels, such reduction tendencies were less significant with an increase of the contact opening speed from 20mm/s to 200mm/s, even when operated to break a load current of 5A. Both load current levels and contact opening speed levels seem to exhibit certain roles for realizing arc shortening effects.