Numerical simulation of multi-component arcs in high-current vacuum interrupters

A transient three-dimensional numerical model has been developed to describe a diffuse multi-component vacuum arc between copper-chromium (CuCr) electrodes under the influence of an axial magnetic field (AMF). The model is based on a two-temperature magneto-hydrodynamic approach of the plasma and is realized with commercial simulation software (CFX) and in-house extensions. The quasi-neutral plasma is described as a two-fluid system distinguishing between electrons and multiply ionized heavy particles. The heavy particles are treated as a multi-component fluid containing Cu ions and Cr ions. The model incorporates balance equations for the ion momentum, balance equations for the ion and electron energy, and transport equations for the magnetic flux density and the radiation. The plasma parameters near the cathode are specified in terms of a self-consistent space-resolved numerical model of the cathode spot on CuCr contacts taking into account the granular structure of the contact material. The simulation is performed at different times during a 50 Hz electrical current cycle. Results are presented for plasma flows under realistic conditions referring to the geometry (140 mm diameter, 11 mm gap), the material (CuCr), and the spatio-temporal AMF profiles of a cup-shaped AMF contact system in an industrial high-current vacuum interrupter (72 kA). Depending on the characteristics of the mass flow near the cathode, distinct features of the energy transport onto the anode are calculated.