GB655111A - Improvements in and relating to resistance units for electric circuit breakers - Google Patents

Abstract

655,111. Wire resistances ; casings, enclosures and mountings for resistances. BRITISH THOMSON-HOUSTON CO., Ltd. March 25, 1948, No. 8857. Convention date, March 26, 1947. [Class 37] [Also in Group XXXVII] A shunt resistor unit 9 shown as applied to the multi-break oil-blast circuit breaker disclosed in Specification 644,392, [Group XXXVII], is of thin part-cylindrical form, thereby possessing small volume, and permitting it to be secured to the cylindrical interrupters 2 without obstructing the blast ports 13. Each resistor unit 9 comprises an arcuate core 19 of strong hot-moulded insulating material and formed on both sides with parallel grooves 22, the grooves on opposite sides being relatively staggered. The resistance wire 21, of, say, 0.03 inch diameter, is first coiled into a helical spring about “ inch diameter and then one end 21a is clamped between a washer 24 and flanged tubular terminal 23 in the top end of the core 19, Fig. 6, the coiled wire then being wound round the core 19 and similarly secured at the bottom end by a tubular terminal 27. During this winding the wire beds into the grooves on the convex side of the core 19 and the portions which stretch straight across on the concave side are brought opposite their respective grooves by opening up one turn of the wire when passing from one side of the core to the other. This assembly may now be applied to an interrupter 2, the cylindrical wall of which will stretch the straight resistance portions and press them into their appointed grooves. As shown, however, the wound core 19 is sandwiched between curved insulating members 18, 20, the parts 18, 19, 20 being held together by shouldered fibre spacers 28 and screws 29. A row of spacers 28 and screws 29 are provided at each end of the resistor unit, and for long units there is an additional central row, in which case a gap 26 is provided in the winding 21 and the grooves 22 are preferably omitted from the corresponding portion of the core 19. The unit 9 is mounted on the interrupter 2 by two pairs of screws 30, 31, accessible through holes 35 in the member 20. The screws 30 extend through the tubular terminals 23, 27 and also serve to connect the resistor to metal parts 17, 16 which are connected respectively to the uppermost and lowermost contacts in the interrupter. The screws 31 extend through similar tubular members 32. Insulating spacers 33 secured to the core 19 by the tubular terminals or members such as 23 extend through holes 34 in the member 18 and thus transfer the mounting pressure to the core 19. The wire 21 is completely protected by bending the edges of the member 20, and may be insulated by filling the unit 9 with a thermosetting compound, this arrangement being suitable .for an air-blast interrupter. Specification 3561/44 (as open to inspection under Sect. 91), also is referred to.