Cathode spot motion in high-current vacuum arcs under self-generated azimuthal and applied axial magnetic fields

Abstract

The motion of vacuum arc cathode spots under the influence of self-generated azimuthal and externally applied axial magnetic fields has been investigated for several metals at currents up to about 10 kA. The spot motion was recorded by means of a high-speed framing camera, and the self-generated magnetic field was measured with an inductive magnetic probe. The axial magnetic field was applied by means of two coils round the vacuum chamber in an approximate Helmholtz arrangement. The data have been used to determine the relationships between the retrograde (anti-Amperian) spot velocity and the self and axial magnetic flux densities. At low self-generated fields, the velocity is directly proportional to the flux density but at high fields velocity saturation is observed in some cases. An axial magnetic field decreased the retrograde velocities on all metals investigated. The spontaneous spot formation observed with high rates of current rise is analysed; the velocity saturation phenomenon is explained semiquantitatively and the influence of the axial magnetic field on the cathode spot velocity discussed.

Investigation of cathode spot characteristics in vacuum under transverse magnetic field (TMF) contacts

“…Then, the relation between the diameter and time was calculated by polynomial fitting. Finally, the radial expansion speed of the cathode spots was calculated by taking the derivative of this expression [10]. In the experiment, there was a certain angle between the direction of the high speed camera and the cathode surface.…”

Statistical Simulation on the Random and Retrograde Motion of Single Cathode Spot of Vacuum Arc

“…Agarwal and Holmes 8) investigated the macrovelocity of the retrograde motion of CS in self-generated azimuthal magneticˆeld for diŠerent cathode materials. It was found that the cathode material with lower vapour pressure near cathode surface, e.g., tin, had higher retrograde motion speed than that with higher vapour pressure near cathode surface, e.g., cadmium 8) . Since the macro-velocity of CS is closely related to the probability of each jump of CS in diŠerent directions, it can be deemed qualitatively that cathode material with lower vapour pressure near cathode surface has higher probability of the jump of CS in the retrograde direction, i.e., larger value of the parameter, k, under same TMF.…”

Investigation of unstable motion characteristics of vacuum arc cathode spots between transverse magnetic field contacts

“…Currently, research on the spot characteristics of high‐current vacuum arc cathode mainly focuses on the influencing factors of the motion characteristics of the cathode spot under flat contacts and axial magnetic field (AMF) contacts without external magnetic field and the influence of external AMF and transverse magnetic field (TMF) on cathode spot under flat contacts. Agarwal and Chaly et al studied the initial diffusion velocity of large‐current vacuum arc cathode spots under the action of external AMF. It was found that increasing AMF would significantly reduce the reverse velocity of cathode spots.…”