GB298567A - Improvements in and relating to induction motors - Google Patents

Abstract

298,567. British Thomson-Houston Co., Ltd., (Assignees of Morrill, W. J.). Oct. 11, 1927, [Convention date]. Alternating - current induction machines.- Relates to electric motors with two squirrel-cage windings and provided with means for automatically varying the reluctance of the flux path in such a way that at starting the outer winding is predominant but as the motor speeds up the work is taken over by the inner winding. For this purpose the outer winding 13 and inner winding 14 are arranged in the same slots and in each slot between the two windings is placed a bar 18 of magnetic material. The outer part of the slot is wider than the bar 18 as shown, but the sides converge inwards to provide a seating for the bar clear of the winding 14. When the motor is at rest or running slowly the bar 18 rests against the seating referred to as shown in Fig. 2, thus forming a magnetic bridge across the slot between the two windings. When the speed increases the bar 18 is thrown outwards as shown in Fig. 4, leaving an air gap in the slot. To prevent the bar from sticking to the sides of the slot between the two windings, spacing pieces 21 of nonmagnetic material projecting into the slot may be arranged between some of the laminations. All or some of the bars 18 may be tubular. The arrangement may be used in a motor starting on a split-phase current which is changed to single-phase as the motor speeds up by a switch operated by a centrifugal governor. Specifications 237,911, 274,878 and 281,706 are referred to.