Effective arcing contact gap of a 126 kV horseshoe type axial magnetic field vacuum interrupter

The objective of this paper is to determine the arcing contact gap for a 126 kV horseshoe type bipolar axial magnetic field (AMF) vacuum interrupter. A pair of contacts with contact material of CuCr50 was arranged in a demountable vacuum chamber. Movable contact was driven by a spring driven permanent magnetic actuator. The full contact gap was 60 mm. Arc current reached up to 40 kA rms, and arc duration was set as 9ms. Evolution of vacuum arc behaviors was observed by a high-speed digital camera. A long arcing contact gap is the maximum gap above which vacuum arcs cannot be controlled by the bipolar AMF. A short arcing contact gap is the minimum gap below which vacuum arcs are constrict. Experimental results show that the long arcing contact gap of the horseshoe type AMF contact is determined as 35 mm, in which the vacuum arc can be controlled by the AMF effectively. The short arcing contact gap is determined as 14 mm. In addition, a recommended arcing contact gap without arc distorting outside is determined as 27 mm. The long arcing contact gap and short arcing contact gap can be used to determine opening speed curve of the 126 kV horseshoe type bipolar AMF vacuum interrupter.