GB1283354A - Improvements in or relating to coils for electrical apparatus - Google Patents

Abstract

1283354 Transformers and inductors MIDLAND TRANSFORMER Ltd 12 Nov 1969 [13 Aug 1968] 38580/68 Heading HIT A coil for a variable transformer, choke or motor starter with an outer surface which is traversed longitudinally by movable tapping contacts is made from a number of preferably identical elements 10, 11 spirally wound from strip of rectangular section and assembled side by side, with alternate elements rotated so that their turns spiral in the opposite sense. A series winding is then formed by interconnecting the starts such as 13, 15 of alternate pairs of adjacent coil elements e.g. 21-22, 23-24 by means of longitudinal bars 28, 30 within the coil and by interconnecting the finishes of the remaining alternate pairs of adjacent elements as at 27, 29. The finishes may project radially from the coil as at 14, 16 and be strapped together, or they may be joined edge to edge to form smooth transitions as shown in Fig. 4. The coil elements may be rectangular so that a flat coil surface (see Fig. 5) is presented to a brass and a carbon roller or brush contact connected in parallel. Alternate coil elements 36, 38, 40 have portions adjacent their finishes 54, 55 which extend right across the coil face as at 48a, 48b and 46a, 46b whereas intervening elements 37, 39 have portions extending only half way across the coil as at 47. Broad insulating strips 49 prevent the brass roller from bridging coil elements as it travels along a longitudinal path between lines 51, 52 while the carbon contact travels along a similar path between lines 51, 53 and bridges adjacent coil elements across narrow insulation strips 50 to preserve continuity of supply. The tapping contacts may move in synchronism or in a stepwise manner, preferably with snap-action to prevent overheating of the carbon contact.