Simulation of external magnetic flux density of moving arcs in vacuum bottles

Vacuum circuit breakers are well established in the distribution levels of the electrical power grids. To minimize contact erosion, an RMF-contact design forces the arc to rotate. The performance of the RMF-contact designs is usually evaluated in specific model vacuum chambers with viewing ports allowing high speed cameras to observe the arc rotation. These setups differ significantly from commercial vacuum bottles in geometry and due to the fact that the main metallic vapor shield is generally not present or is significantly modified. This in turn can affect the arc rotation behavior. In order to overcome these shortcomings, a new diagnostic tool is being developed to analyze the arcing behavior in standard commercially available, sealed vacuum interrupters. Optical methods are not possible, since the view is blocked by the opaque ceramics and the metallic vapor shield. However, the magnetic field permeates the housing, and thus the new diagnostic tool evaluates the arc movement with externally mounted Hall sensors. However, eddy currents in the vapor shield affect the magnetic flux density. This paper presents 3D-simulations of a moving metal vapor arc, the corresponding eddy currents in surrounding metal parts and the final magnetic flux densities. With this information, a moving vacuum arcing can be characterized via a Hall sensor based measurement system.