GB168849A - Improvements in or relating to automatic electric circuit breakers - Google Patents

Abstract

168,849. MÚtallurgique Electrique. Sept. 6, 1920, [Convention date]. Automatic circuit - breakers; electromagnetic switches. - To deal with small overloads a circuit-breaker is provided with ordinary overload tripping mechanism which first introduces a limiting resistance into the main circuit and finally breaks the circuit at sparking contacts while, to deal with heavy overloads or short-circuits, the circuit-breaker is opened rapidly by electromagnetic means before the relatively slow-acting tripping mechanism comes into action. As shown in Fig. 1, the threearmed switch lever A carrying the main contact 3 is pivoted at 5 and has pivoted upon it, with slight lost-motion, two independently-movable sparking contact levers 10, 11. The arm 5, 7 has a loose connection, which is maintained by a spring 17, with the switch-operating and tripping mechanism within the box 15. The shunt tripping coil is shown at 18. With an ordinary overload, the main current which passes through the coil of a heavy magnet 25 energizes the tripping coil sufficiently to operate the trip, whereupon the three-armed lever swings round, first withdrawing the main contact 3 and introducing the resistance 13 into the main circuit, then withdrawing the contact 11 from the contact 10 and, finally, breaking the circuit by withdrawing the contact 10 from the fixed sparking contact. In the event of a heavy overload, however, the heavy series magnet 25 attracts its armature 23 and pulls over the lever 21. 19 against the action of an adjustable shunt-retaining magnet. The lever 21, 19 has a one-way connection with the link 19, 6 and pulls over the three-armed switch lever to the off position directly, even before the tripping mechanism operates. In this movement, the spring 17 is compressed, but immediately afterwards the tripping mechanism acts and the spring is again relaxed. The number of auxiliary sparking levers may be increased to allow of the resistance 13 being inserted in stages. The heavy operating magnet 25 and its armature 23 are preferably of the form shown in Fig. 7, with an additional air gap in which the sparking contacts are located so that the operating magnet may provide the blow-out field.