Takayoshi Kubono

Rotational Drive of Break Arcs Using a Permanent Magnet Embedded in an Electrical Contact

Break arcs are generated between silver electrical contacts in a DC 42V resistive circuit. Circuit current when the contacts are closed is varied from 5A to 21A. Break arcs are driven by the radial magnetic field that is formed between the electrical contacts with a permanent magnet embedded in the cathode. The arc motion is taken with a high-speed camera and contact surfaces are observed after break operations. Experimental results with the magnet are compared with those without the magnet to confirm the effect of the embedded magnet. For break operations with the magnet following results are shown for each circuit current. Break arcs are rotationally driven by the radial magnetic field in the direction according to Lorentz force. The shortening effect of the arc duration is confirmed. The traces of the arc spots on the contact surfaces are ring-shaped, wide and uniform. This result shows the prevention effect of local erosion of electrical contacts. The rotational frequency is increased by the increase of Lorentz force to drive the break arc rotationally with the increase of the arc current.

Characteristics of Break Arcs Driven by External Magnetic Field in a DC42V Resistive Circuit

Break arcs occurring between electrical contacts are driven by the external magnetic field. Break arcs are observed using a high-speed camera. The external magnetic field is applied with a permanent magnet. The distance between the electrical contacts and the magnet is varied. Experimental circuit is DC 42 V-10 A resistive circuit. Material of electrical contacts is pure silver. The opening speed of electrical contacts is varied as 5, 10 and 20 mm/s. Following results are shown. The arc duration decreases with decrease of the distance between the electrical contacts and the magnet. When the magnetic-flux density applied by the external magnet is lower than a certain value at the center axis of the electrical contacts, the effect of the magnetic field to drive the break arc becomes ineffective to shorten the arc duration. The result is explained with a relationship between the motion of break arc and the distribution of the external magnetic field.