GB418615A - Improvements in or relating to protective control systems for electric motors - Google Patents

Abstract

418,615. Protective cut-out arrangements and automatic circuit-breakers; control of motors. BROOKE, W., Braemar, Laburnum Lane, Hale, Cheshire. Aug. 17, 1933, No. 22964. [Classes 38 (iii) and 38 (v).] In a remote control system for an electric motor B, operating a coal cutter &c., and connected by a trailing cable U to control mechanism A and supply lines L<1>, L<2>, L<3>, the motor supply circuit is opened if connection is made between the pilot core Y and earth core Z other than by closure of an operating switch G, by associating opposed rectifiers m, n and inductances h<1>, h<2> with the energizing circuit of a relay k which initiates operation of the main motor contactor C. Closure of operating switch G energizes relay k with direct current from a transformer g thereby completing the energizing circuit of a relay f whose contacts r are included in the energizing circuit of the main contactor coil d. In closing, the main contactor C opens auxiliary contacts c<5> included in its energizing circuit, but is retained closed by a mechanical catch associated with relay f as long as the latter remains closed. If a short circuit occurs between cores Y and Z, alternating current is supplied to contactor coil k but is suppressed sufficiently to prevent operation (by inductances h<1>, h<2>). The contacts c<1>, c<2>, c<3> of contactor C are carried on a pivoted arm 20, Fig. 3, having an extension connected with toggle links 29, 30 co-operating with a pivoted lever 33 engaged through a spring 37 by the moving member 36 of contactor f. When contactor f is energized, the spring 37 is strained so that when contactor C closes, an extension 33<a> on lever 33 retaining the links 29, 30 in the extended position until contactor f is deenergized. Switch G may be retractive, and its circuit maintained through the contacts of an electromagnetic switch energized from two of the motor supply leads, so that, in the event of the supply failing, the motor does not start with the resumption of the supply until the switch is operated.