GB806486A - Improvements in or relating to induction motors - Google Patents

Abstract

806,486. Change-pole windings for dynamoelectric machines. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 4, 1957 [Feb. 14, 1956], No. 4617/56. Class 35. A 3: 1 pole-changing winding consists of a three-phase, four-pole delta winding which is opened at one corner and fed in series to provide a single-phase, twelve-pole winding, two other twelve-pole windings being wound in the same stator to give a complete three-phase winding which may be connected in star or delta. As shown in Fig. 1 for a twelve-pole star connection the four-pole delta winding 1, 2 ; 2, 3; and 3, 4 is normally fed at l1, 12, 13, but is opened for twelve-pole operation at switch s1. The additional coils 4, 5 and 4, 6 complete the threephase winding fed, as shown, through terminals L1, L2, L3. The pole-change is thus achieved with only the six terminals 1-6. A similar arrangement is described for the delta connection. It is necessary to use three, or a multiple of three, slots per pole per phase. Preferably three slots per pole-phase are used, the four-pole winding distribution being modified by concentrating half of the conductors in the central slot and a quarter each in the outer slots to provide space for the additional twelve-pole windings in these slots. This arrangement has the additional advantage of reducing the 7th harmonic at the four-pole connection. Preferably, the four-pole conductors in the outer slots are slightly reduced in gauge so that they occupy less than half of the slot, the greater part, e.g. two-thirds, being taken by the additional twelve-pole windings which may have a reduced number of turns. The outer slots may alternatively be deeper to hold the two windings without reducing the gauge of wire. Preferably, the twelve-pole winding is at the top of the slots. Saturation of the core may be employed at the higher speed. By reversing alternate coil groups in the four-pole winding connection, the machine may be made to run at two-pole speed. For this purpose, as shown in Fig. 7, the coils 1, 2 ; 2, 3 and 3, 4 are centre-tapped and supplied at terminals 7, 9, 11 to produce a parallelstar connection. It is described how, in addition, the winding may be connected to give a six-pole parallel-star arrangement in which the supply is connected to terminals 7, 12, 13. Specification 797,290 is referred to.