GB172433A - Improvements in and relating to overload electric switches - Google Patents

Abstract

172,433. Rogers, T. W., (Krupp Akt.- Ges., F.). Sept. 16, 1920. Electromagnetic switches; ratchet operation; protective arrangements.-In order to interpose an adjustable delay-action before the operation of an overload switch, the overload is caused to move the contact-arm of an electromagnetic relay step-by-step to the closed position, whereupon the overload switch is energized to open the circuit. If the overload ceases before the step-bystep relay closes, the relay returns to its initial position, and, if a very heavy overload occurs, the main switch is actuated at once. As shown applied to the overload protection of a motor D, an overload on the motor energizes the winding H of the step-by-step relay sufficiently to move the core G and propel the ratchet-wheel K one step, moving the contact-arm k<2> towards the adjustable contact k<5>, the ratchet wheel being held, against spring return, by a pawl p<2> held down by the core of the winding Q carrying the motor current. The movement of the core G separates contacts g<1>, g<2> and removes a short-circuit from the winding H<1>, which is equal and oppositely wound to the coil H. As a result the core rises again and, if the overload persists, the ratchetwheel is again moved on until, finally, the relay circuit is closed. If the overload ceases, the reduced current in the winding Q allows the pawl p<2> to be removed by its spring and the relay returns. A short-circuited damping winding J is provided on the.relay core. When the relay closes, the shunt coil C is energized and, acting additively to the series winding B, opens the overload switch. The main circuit is opened but the coil C remains excited through the resistance F, coils Q, H, and contacts g<1>, g<2>; this excitation is adequate to hold the switch open until the holding circuit is broken by a hand switch. In the event of a very heavy overload the coil B operates to open the switch at once.