Vacuum-Arc Behaviors of a Coil-Type Axial-Magnetic-Field Contact at Contact Gap of 60 mm

Contact gap is usually high in high-voltage vacuum circuit breakers (VCBs). We experimentally investigated vacuum-arc behaviors of a coil-type axial-magnetic-fleld (AMF) contact with a contact diameter of 100 mm and a contact gap of 60 mm, which included vacuum-arc appearance observation and LC discharging current interrupting test. The vacuum arc was ignited by a trigger needle in a demountable vacuum chamber, and the vacuum-arc appearance was recorded by a high-speed charge-coupled-device camera. The LC discharging current interrupting tests were done by using a VCB with the coil-type AMF contacts in the vacuum interrupters. Vacuum-arc appearance with current peak values of 11.3, 17.0, and 22.7 kA (current frequency of 50 Hz) was shown in diffuse mode, although there was an unstable period at the beginning of arcing period. The LC discharging current interrupting test showed that there was no second half-wave until a 50-kA rms current. When the contact gap increases from 40 to 60 mm, arc-voltage noise oscillation increases, and arc voltage at current peak almost doubled in the range of arc current from 10 to 50 kA. When the peak arc-current value increases from 11.3 to 17.0 and 22.7 kA, both the arc-voltage noise amplitude and the arc-voltage noise duration increase.