Arcing Contact Gap of a 126-kV Horseshoe-Type Bipolar Axial Magnetic Field Vacuum Interrupters

The objective of this paper is to determine arcing contact gap of a 126-kV horseshoe-type bipolar axial magnetic field vacuum interrupter. Drawn arc experiments were carried out in a demountable vacuum. Experimental current ranged from 12-to 40-kA rms. Based on the vacuum arc behavior, minimum arcing contact gap D-1 and maximum arcing contact gap D-2 were defined. When average opening speed within 20 mm (v(1)) was 1.9, 2.3, and 2.6 m/s, D-1 was determined as 15.3, 16.8, and 14.3 mm, respectively. In addition, D-1 reflected a peak effect with v1. When average opening speed within 40 mm (v(2)) was 2.6, 2.7, and 2.8 m/s, D-2 was determined as 38.5, 36.7, and 36.1 mm, respectively. Uncontrollable arc mode appeared when current was higher than 32 kA with arc duration of 9 ms. The critical contact gap to avoid uncontrollable arc mode decreased as a liner function of arc current. Based on the experimental results, quantitative design method of three-interval opening velocity for the 126-kV horseshoe-type vacuum circuit breaker was proposed. For short-circuit current interruption test duty T100s, lower limit value of v(1) and upper limit value of v(2) were determined as 2.5 and 2.9 m/s with a prospective minimum arcing time of 7 ms.