Decay Modes of Anode Surface Temperature After Current Zero in Vacuum Arcs-Part I: Experimental Study

Anode surface temperature has a significant impact on the interruption capacity of a vacuum circuit breaker. The objective of this paper is to experimentally understand the decay process of anode surface temperature after extinguishing a high-vacuum arc with a large contact gap. The anode surface temperature after current zero was measured by a two-color pyrometer and arc modes observation was recorded by a highspeed charge-coupled device. A pair of asymmetric butt type contacts (contact materials: CuCr25 and CuCr50) was subjected to an axial magnetic field in a demountable vacuum chamber. The experimental result shows that there are two modes in decay processes of anode surface temperature: Mode I and Mode II. Mode I describes the anode surface decay process after diffuse low-current extinction and Mode II corresponds to high current extinction. In addition, the decay time of anode surface temperature will last longer, if the proportion of chromium rises from 25% to 50% in anode material.

I. Introduction

In VACUUM interrupters (VIs), anode surface condition after current zero is a significant influential factor for a successful interruption because a hot anode surface that is also the post-arc cathode will evaporate an amount of metal vapor that dominates the dielectric recovery strength of the VIs directly [1], [2]. In addition, metal vapor is expected to be positively correlated with the anode surface temperature. Thus, a dielectric recovery process will be retarded seriously if the anode surface is still high after current zero, especially when the surface remains in a molten state. For this reason, axial magnetic field (AMF) [3] and transverse magnetic field (also known as radial magnetic field) [4] technologies are adopted to control arc energy input into contact surfaces and make sure that there is no overheating on the surfaces ensuring a successful interruption.