Patent GB-682588-A (GB)
Title: Improvements in or relating to alternating current electric motor arrangements
IPC: H02K17/04
Filed: 1949-04-13
Abstract: 682,588 Electric motors. GENERAL ELECTRIC CO., Ltd., and FRIEDLANDER, E. S. July 13, 1950 [April 13, 1949], No. 10043/49. Class 35. In a single-phase A.C. motor having a plurality of stator poles and an unpolarized rotor having a fewer number of poles, the distribution of the alternating flux between the stator poles is controlled in dependence on the rotation of the rotor by means of contacts, saturation or resonance effects. In its simplest form, Fig. 1, opposite windings 16, 17, and 19, 20 of a four-pole stator are connected in series and in series or parallel with condensers 18, 21. The condenser values are such that resonance at the supply frequency takes place when the inductance of the stator windings is least, i.e. when the rotor 15 is in such a position that its poles are not opposite those particular stator poles carrying the winding. Resonance causes an increase in the flux carried by the poles concerned and the rotor moves to this position, which, in turn, displaces the resonance condition to the adjacent set of poles. Starting devices of various kinds may be fitted while the stator and rotor may have other numbers of poles which need not be of salient form and the air-gap may be of sinusoidal form. The motor speed may be by altering the condenser values and if resonance occurs in the position where the poles are opposite each other, the motor will come to rest. In a modified form, Fig. 2, the resonance current induced in windings 71-76 on a series of exciter poles 41-46, is used to energize saturating windings 61-66 on the main poles 31-36 which are energized by main windings 51-56 fed directly from the A.C. supply. Exciter windings on opposite poles, e.g. 71 and 74, are connected across the A.C. supply in series with a resonating condenser and a bridge connected rectifier whose D.C. output is fed to the saturating winding, e.g. 61 and 64 of the adjacent main pole to control the flux produced by the main windings 51 and 54. The condenser values are such that resonance occurs when there is minimum overlap between the armature and main poles. The condensers may be omitted, in which case, the exciter poles may have to be moved relatively to the main poles. This is facilitated by making the main and exciter poles as separate magnetic systems and co-operating with separate rotors displaced by a suitable angle. Relative rotation between the two stators may be used to control the motor speed and direction. In non-salient pole forms, the stator windings are fixed in slots with the main windings at the mouth of each slot and the saturating winding at the bottom, and there may be magnetic bridges in the slots between these two windings. Alternatively, the saturating windings may extend through ducts in the stator core below the slots. Instead of salient poles, the rotor may carry short-circuited windings in one plane, so that the machine may be adapted to run as an induction motor at speeds near synchronism. It is stated that the magnetic amplifying effect of saturating windings controlling the main flux need not be incorporated into the machine itself but may be separate, the exciter unit being on the motor shaft to act as a magnetic commutator, in fact, it may be replaced by a mechanical commutator cyclically feeding the magnetizing windings on the main poles. The saturating and main windings on the main poles may be disposed so as to use the same copper and the exciter and main machines need not be coupled together. A single pilot exciter may be used to control the cyclic excitation of several motors, e.g. for position control.