Patent GB-190923553-A (GB)
Title: Improvements in or relating to Windings for Alternating Current Motors.
Inventor: STERN MANU
IPC: H02K17/14
Filed: 1909-10-14
Granted: 1910-10-13
Abstract: 23,553. Stern, M. Oct. 31, 1908, [Convention date]. Alternating - current induction machines; windings.- In induction motors, the speed of which is varied by changing the connexions of the stator winding so as to produce, from a three-phase winding having 8 n poles, a two - phase winding having 6 n poles, and vice versa, as described in Specification 12,326/08. the connexions of the armature coils are correspondingly varied. The winding of each phase of the threephase 8-pole armature winding shown in Figs. 1 and 3, consists, as regards phase 1, of coils 1<a>, lb and 1<c>, 1<d>, those coils which are arranged apart at a distance of 720 electrical degrees from each other being connected in series ; the two groups 1<a>, 1<b> and 1<c>, 1<d> thus obtained are displaced by 360 electrical degrees and are connected in parallel either in star or in mesh, Fig. 3, to the main sliprings 1, 2, 3. Points y<4>, y<7>, which are equipotential with reference to the slip-rings 1, 2, are connected to additional slip-rings 4, 7, and similar points in the other two phases are connected to additional slip-rings 5, 6, 8, 9. When the stator winding is connected for 8 poles, the additional slip-rings are inoperative, and the brushes sliding upon the main slip-rings 1, 2, 3 are connected with the starting resistances, on to a second motor in cascade. When the winding is changed to the two-phase 6-pole form, the slip-rings are connected together in groups by conductors e, f, g, the leads L<1>, L<11>, L‹ showing the conductors of the two phases. The additional slip-rings may be dispensed with, if, between the equipotential points y<4>, y<7>, &c. of each phase, there are connected two resistances r, Fig. 4, between which is branched off a wire s leading to one of the main slip-rings 1, 2, 3. Each wire s is then provided with a contact k, which is open during the three-phase working and closed during the two-phase working. The above winding may be used on the stator. The Specification, in the original form, as open to inspection under Section 91 (3) (a), comprises also the following subject-matter. In one modification, seven slip-rings only are required; each phase of the windmg being divided into four portions connected up in star-fashion to four sliprings, which serve as terminals for two-phase working and as equipotential connexions for threephase working. Similar windings having equipotential connexions may be arranged in such a manner that they are automatically short-circuited when changing over to one number of poles ; at least two coils in each phase, which are separated by (2n-1).720 electrical degrees, are connected in opposition to each other for three-phase working. According to one arrangement, a "loop" winding, which is short-circuited by equipotential connexions for one pole-number, is short-circuited for another pole-number by outer connexions only, points on the winding which are equipotential for working with 8 n poles, being connected together by at least three connexions situated at equal distances from each other. This subject-matter does not appear in the Specification as accepted.