Anode Input Heat Flux Density in High-Current Vacuum Arcs as Anode Spot Formation

In vacuum interrupters, anode spot significantly decreases the current interruption capability. Generally, the anode spot is evaluated by the anode spot threshold current. Unfortunately, as a circuit parameter, arc current cannot explain the anode spot formation from the physical point of view. This work proposes the heat flux density as a new parameter to evaluate the anode spot. The objective of this study is to determine the anode input heat flux density as anode spot formation. The heat flux density is numerically obtained by a two-temperature magnetohydrodynamic model. Based on a previous systematic experimental work over a wide range of discharge conditions, the calculated critical anode input heat flux density located in a narrow range from
$7.3\times 10^{8}$
to
$11.3\times 10^{8}$
W/
$\text{m}^{2}$
. Compared with the arc current, the anode input heat flux density is a key parameter in the interaction between the vacuum arc column and the anode; moreover, the heat flux density has a close relationship with both the arc distribution and the anode activity. Therefore, heat flux density is a reasonable physical parameter to reveal the mechanism of the anode spot formation.