Patent GB-1221647-A (GB)
Title: Improvements in or relating to electrical apparatus
Inventor: HINKSMAN ERNEST ALAN
IPC: H01F29/06
Filed: 1967-07-13
Abstract: 1,221,647. Transformers; inductors; mechchanical switches; tap changers. MIDLAND TRANSFORMER CO. Ltd. 12 July, 1968 [13 July, 1967; 24 May, 1968], Nos. 32266/67 and 25037/68. Headings HlN and HIT. [Also in Division H2] A movable tapping arrangement for the coil of an electrical apparatus, e.g. a voltage regulator, transformer or choke, comprises one or more assemblies, each of which comprises a first element contacting the turns of the coil and arranged to break contact with one turn before making contact with the next, and a second element arranged to provide a resistance in the load current path as the first element makes and breaks said contact, means being provided to move the two elements in synchronism. In one embodiment (Fig. 1) the first and second elements comprise a brass roller 45 and a carbon (or metal-carbon mixture) roller 46 respectively, both spring-urged against the turns 21 of a helical coil 20. The two rollers are moved along the coil by rotation of shaft 38 having a helical track 37 engaged by screws 36 on the contact assembly. The inter-turn insulation is made flush with the surface of the coil along the path followed by roller 45 but not along the path followed by roller 46, so that the latter is able to bridge adjacent turns when the former is out of contact with both of them. Brass and carbon brushes disposed side by side may be used instead of rollers (Figs. 7-9, not shown), the brass brushes (90) being cut away (as at 97) to ensure that only the carbon brush (89) can bridge adjacent turns. Alternatively two brushes may be disposed one behind the other rather than side by side, as 73, 74, Fig. 5. In all these embodiments more than one roller or brush may be used to constitute each element. A further embodiment uses a single roller whose periphery comprises parts of high conductivity separated by parts of lower conductivity, the latter parts being arranged to contact the coil while the roller is moving from one turn to the next. In a final embodiment (Fig. 10) an assembly 100 comprises two brass discs 101, arranged so that at least one of them is always in contact with a turn, bolted to respective take-off discs 114, each of which has an insert of carbon and contacts a respective feeder disc 122 slidable and rotatable on spindle 123. The whole assembly 100 rotates about a shaft 109 disposed parallel to the axis of the coil and simultaneously moves along that shaft in such a way that as a brass disc 101 breaks or makes contact with a turn the respective carbon insert comes into the load circuit. An insulating peripheral portion of each disc 101 breaks the electrical contact between the disc and a turn before the disc moves off that turn. Contact strips, such as 29, Fig. 1, and 66, Fig. 5, may be attached to each coil turn, the strips extending across at least part of the surface 24 of the turns and projecting beyond the coil to provide heat-dissipating fins. Alternatively, the turns may have a cross-section in the shape of an inverted T. The tapping assembly is moved from turn to turn in jerks, e.g. by an electric motor driving shaft 38 through a Geneva motion in conjunction with a snap-action mechanism (Fig. 4, not shown). In the arrangement of Fig. 10, the tapping assembly is connected to the load by means of a centre-tapped choke connected between the two spindles 123. In the other embodiments, sprung carbon or metal brush(es) as 54, Fig. 1, or 129, 134, Fig. 17 (not shown), running against a fixed bar 56, (125), is used, no choke being needed.