GB601729A - An improved electric motor protection switch - Google Patents

Abstract

601,729. Electrically-tripped switches. LANDIS & GYR SOC. ANON. Feb. 13, 1945, No. 3573. Convention date, Feb. 21, 1944: [Class 38 (v)] The time-lag and quick-acting releases for a motor-protection switch are simultaneously adjustable to the rated current and a multiple thereof respectively and are combined in a small box which forms a constructional unit for insertion in the switch. The moving contacts 1 of a three-pole switch are actuated by an electromagnet (not shown) which has a switch 15 in its energizing circuit. The normally fixed contacts 2 are mounted on insulating slides 3 biassed away from the contacts 1, but latched-in by detents 6 engaging half-cylinders 7, each carried by a two-arm lever 9, 10 pivoted coaxially with the halfcylinders 7. The motor current in each pole flows through contacts 1, 2, co-operating contacts on the switch and the box, the winding 33 of a relay, a bimetal strip 18 and further contacts on the box and switch. On normal overload, the strip 18 flexes about its fixed end 18a and raises a screw 21 to rotate a shaft 19 and a half-cylinder 19a, allowing a lever 25 to pivot about a lever 26 and bpen at 15 the energizing circuit of the switch-holding magnet, thereby opening all poles. On short-circuit, the winding 33 attracts an armature 34, which strikes the lever 10 to unlatch the contact 2 at 7, 6 and open one pole. As the slide 3 moves back, it strikes a manual re-set lever 13, 14 which, by striking an abutment 16, opens the switch 15, de-energizing the switch-holding magnet and opening all poles. The relays, bimetal strips, shaft 19 and levers 25, 26 are mounted as a unit in a box 17 together with a shaft 30 carrying cams 28, 29 and a slotted disc 37. By turning the disc 37, which indicates the rated current, the cams 28, 29 adjust the release point of the latch 19a, 25 and the tractive power of springs 35, to vary the operating currents for the bimetal strips and the relays, respectively. This adjustment maintains a constant ratio of operating currents, which is set by prior adjustment of screws 21, 36. Quenching chambers 5 house the contacts 1, 2 and one or more quenching coils 4. Specifications 588,724 and 588,738 are referred to.