Rotational Drive of Arc Discharges by a Permanent Magnet Embedded in an Electrical Contact Mounted on a Relay

A column-shaped permanent magnet is embedded in the center of an electrical contact mounted on a relay. Another contact is conventional shape without the magnet. The magnet forms radial magnetic field to rotate arcs around the center axis of electrical contacts. A series of experiments is carried out in a 42V-10A resistive circuit. The contact material is Ag/SnO₂ 12wt%. The electrical contacts that are used in switches on the circuit current are called the make-only contacts, and switches off the circuit current are called the break-only contacts. Experimental results for make-only and break-only operations with the magnet are compared with those without the magnet. Following results are obtained. Rotational motion of the arcs occurring during the contact bounce for make-only operations is not observed. However break arcs for break-only operations are successfully rotated. Without the magnet the area of contact erosion on the contact surfaces is concentrated on the tip of contacts. With the magnet, on the other hand, the area of contact erosion is wide on contact surfaces by the rotational motion of break arcs. For break-only contacts the arc duration with the magnet is almost equal to that without the magnet. These results show that the effect of the magnet is confirmed to uniform the area of contact erosion for break-only contacts and the effect is not remarkable for make-only contacts.