GB706284A - Combined thermal and electro-magnetic overload relay - Google Patents

Abstract

706,284. Electromagnetic switches. MAUPAS C. F. E. March 18, 1952 [March 22, 1951], No 7016/52. Class 38(5) A relay responsive to the current in a coil 14 has a main magnetic circuit 1 controlling an armature 4 and an auxiliary parallel magnetic circuit 2, 3 controlling an armature 5, the armatures 4, 5 being mounted on the same spindle 6 and being normally urged into the position shown by a spring 9 and the auxiliary magnetic circuit having a portion of an alloy which loses its magnetic properties at a temperature, say, of 170‹ which is heated by a current proportional to the current in the winding 14. In the form shown diagrammatically, the portions 2, 3 of the auxiliary magnetic circuit near the armature are made of the special alloy, are connected by a conductor 8 and are heated by the current flowing through them, an adjustable shunt 7 regulating the amount of this current. The magnetic force acting on the auxiliary armature 5 together with the force of the spring 9 oppose the magnetic force acting on the main armature 4. A moderate sustained overload causes the portions 2, 3 to lose their magnetism so that the force on the main armature preponderates and the shaft 6 is rotated to open contacts 12 or operate a trip device. A heavy overload causes the force acting on the armature 5 to increase less rapidly than that acting on the armature 4 with consequential actuation of the contacts. In a modification, Figs. 2, 3 (not shown), the current through parts 2, 8 and 3 is derived from a secondary winding energized transformer fashion from the winding 14. A number of mechanisms may also be associated axially so as to drive a common shaft operating the contacts, Fig. 6 (not shown). In Fig. 5, a spindle 54 corresponding to the spindle 6 of Fig. 1 is latched in operated position by a latch 56 and may later be released by an electromagnet 60.