GB1057730A - Improvements in or relating to electrical switchgear - Google Patents

Abstract

1,057,730. Electromagnetic relays; control of D.C. motors. SECRETARY ARMY, UNITED STATES OF AMERICA. Nov. 25, 1963, No. 46447/63. Headings H2B and H2J. A moving coil relay 6 is designed to maintain constant the direction of current in the field winding of a series wound motor despite reversal of the direction of the current in the armature winding of the motor. The relay 6 comprises a moving coil armature 7, 10, 11 rotatable in the air-gap of a permanent magnet 8. An arm 4 carrying pairs of inter-connected brushes 3a, 3d and 3b, 3c is moved by the armature over the surface of a cylinder 1 carrying four insulated conducting segments 1a, 1b, 1c, 1d, between two positions. In one position brushes 3a, 3d bridge segments 1a, 1d and brushes 3b, 3c bridge segments 1b 1c and in the other position segments 1c, 1d and 1a, 1b are bridged. A generator 14 is connected in series with armature winding 12 and field winding 13 of the motor. The relay 6 is controlled by a shunt-excited relay 19 connected in the motorgenerator circuit. Normally this relay causes energization of coil 10 of relay 6 so that contact brushes 3a, 3b, 3c and 3d occupying the full line position, but when the direction of current in the generator and motor armature winding 12 reverses, relay 19 causes energization of coil 11 and the brushes rotate to the dotted line position thus maintaining the direction of current in field-winding 13 constant. In an alternative arrangement (Fig. 4, not shown) a polarized moving coil relay 6 has only one moving coil which is energized by a shunt in the generatorarmature winding circuit so that relay 19 is unnecessary. In Fig. 2 (not shown) the relay 19 energizes or de-energizes a single moving coil which is spring-biased to one position. In Fig. 3 (not shown) the armature of relay 6 carries a continuously energized moving coil which is controlled by alternate energization of two coils wound on a fixed core in the air-gap of which the coil rotates. Sparking is prevented by capacitors shunted across the segments 1a 1b 1c, 1d. In another embodiment (Fig. 6, not shown) two coils are secured in conducting channels in the armature, the channels acting as short-circuited turns, and erratic movement of the armature is prevented by an hydraulic dash-pot. Stops limit the movement of the armature. To ensure that the armature can only come to rest in its extreme positions the armature may be spring- biased to one position or may be provided with a spring-biased detent. The brushes may be fixed and the cylinder movable.