GB164728A - Improvements relating to protective devices for electric circuits - Google Patents

Abstract

164,728. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Smith, B. H.). June 9, 1920, [Convention date]. Transformers, - Protective devices for electric circuits comprise a thermal relay with a bimetallic member adapted to make and break the circuit through the operating coil of a circuit breaker controlling the protected circuit, the bimetallic member being actuated by the heating effect of energy supplied by the secondary of an auto- 'or two-winding transformer in the circuit controlled. The bimetallic member 16 is supported within a tubular member 7 of magnetic material, side plates 12, 13 of similar material being secured around the member 7, and an outer member 14 completing the magnetic circuit. Within the annular space between the members 7 and 14 are placed the transformer windings 10, 11, insulated metal connecting ferrules 8, 9 closing the ends of the member 7. An insulating shell 15 surrounds the member 14. Fig. 2 shows the connections for a two-winding transformer, the primary winding 11 being connected in series with the protected circuit 2, and the bimetallic member 16 being connected to the secondary winding 10. In Fig. 4 an auto-transformer is employed, the winding 11 being connected in series with the protected circuit, and the bimetallic member 16 connected to a section 10 of the winding 11. The ratio between the primary and secondary windings is such that the current traversing the bimetallic member is greater than the current in the protected circuit. The free end of the bimetallic member carries a contact 18, which normally touches an insulated contact 19, which is connected in the circuit of the holding-on electromagnet of the circuit breaker 3. The elements 7, 12, 13 and 14 of the magnetic circuit of the transformer are slotted to prevent formation of eddy currents. The air space surrounding the member 16 acts as a thermal insulant between the bimetallic strip and the transformer. Specification 114,161, [Class 38 (v), Electric switches &c.], is referred to.