A Relationship Between Vacuum Arc Characteristics and Short-Circuit Current Interrupting Capability at Minimum Arcing Times

Abstract

The study is to explore a relationship between vacuum arc characteristics and short-circuit current interrupting capability of a fast vacuum circuit breaker (FVCB) at a minimum arcing time. Both a short-circuit current interruption test and an arc mode transition observation test were carried out to explore the relationship. Firstly, an FVCB with ceramic enclosure vacuum interrupter (VI), in which a pair of axial magnetic field (AMF) contacts were arranged, was operated with three different opening speeds to interrupt short-circuit currents. A Weil synthetic circuit provided short-circuit currents of 20, 30, and 40 kA, and a transient recovery voltage (TRV) of 92 kV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$120~\mu \text{s}$ </tex-math></inline-formula> for the short-circuit current interruption capability experiment. Then, the arc mode observation experiment was carried out under the same conditions as the short-circuit current interruption capability experiment, except for two differences, that is, a glass enclosure VI without a shield was used for observing the arc with a high-speed camera, and the other point was that only the short-circuit current was applied and no TRV was applied. Experimental results showed that the increase in the opening speed resulted in a decrease in the minimum arcing time, the critical arc extinguishing gap, and the critical arc diffusion time, but led to an increase in the maximum arc column diameter. In contrast, the increase in the short-circuit current would increase the minimum arcing time, the critical arc extinguishing gap, the critical arc diffusion time, and the maximum arc diameter. The diffusion of the arc column is essential but not sufficient for the successful interruption. The contact gap plays a significant role. On the one hand, a larger contact gap promotes arc diffuse. The arc diffusion can decrease the contact surface temperature and the local particle density at current zero. On the other hand, a larger gap distance leads to a smaller electric field intensity between fixed and moveable contacts, which reduces the breakdown probability during the postarc dielectric recovery. The critical arc energy density for a successful interruption of the FVCB in short arcing times was obtained to range from 0.54 to 1.01 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{8}$ </tex-math></inline-formula> J/m3.