Study on the heat flux density delivered to the anode at the transition to anode spot formation in high current vaccum arcs

Abstract

In vacuum interrupters, anode spot formation is commonly known as a high-current anode discharge mode and it significantly decreases the current interruption capacity of the vacuum interrupters. To understand the mechanism of the anode spot formation, the heat flux density delivered to the anode is of vital importance. The objective of this paper is to determine the peak heat flux density at a transition from diffuse arc mode to anode spot formation in high-current vacuum arcs. A three-dimensional magneto-hydrodynamic model is adopted to describe the high current vacuum arcs. Based on the previous experimental data about the anode spot formation, the simulations quantitatively identified the heat flux density at the transition to anode spot formation. The influence of arc currents, contact gaps, and external AMFs are studied. The arc current is from 12 kA to 25 kA. The contact gaps are 12 mm and 6 mm. The external AMFs are 37 mT and 74 mT. At a given current, the peak heat flux density decreases with an increasing of AMF, and increases with an increasing of contact gap. Over the range of the parameters investigated, the heat flux density at anode spot formation is in a narrow range of 6.1 × 108 W/m2∼10.5 × 108W/m2.