Distribution of cathode current density and breaking capacity of medium voltage vacuum interrupters with axial magnetic field

In an earlier work the authors offered a technique of high-speed photography of high-current vacuum arc that, in combination with the special computer-aided treatment, allowed reconstruction of distribution of current density on the cathode. This technique was applied for but solid contacts with external axial magnetic field (AMF) at relatively low current density j < 2 kA/cm2. In the present work this technique is further developed. Ther advanced technique is applicable for the analysis of current density distribution on the complicated electrodcs of commercial vacuum interrupter (VI) cnrrying current up to I = 50kA at current density up to j ~ 4 kA/cm2. The experiments have been carried out for three types of electrode systems generating AMF with different configurations. The obtained results prove previously derived conclusion that current density tends to distribute evenly across that part of the contact surface where AMF induction fits an inequity relation where the characteristic inductions are as defined in the earlier work. Slots on the electrode surface lead to substantial nonuniformity of current density distribution even if the AMF is properly configured.