GB231642A - Improvements in and relating to synchronous electric machines - Google Patents

Abstract

231,642. Shenfer, C., and English Electric Co., Ltd. March 3, 1924. Alternating - cur - rent induction machines; exciting. - In an alternating - current machine having a polyphase winding and continuous-current excitation on one element and a single - phase winding on the other element, an electromotive force is impressed by external means upon the continuous-current circuit approximately equal and opposite to the electromotive force induced therein by the flux of the machine. As shown in Fig. 1, the three-phase primary winding 4 is on the stator and the single-phase short-circuited secondary winding 8 is on the rotor. The stator has also a continuous-current excitation winding 9 fed from an exciter 10 in series with the secondary winding 11 of a transformer. The primary winding 15 of the transformer is connected to an appropriate pair of the alternating-current mains and by a suitable choice of the number of turns of the transformer, the electromotive force impressed on the circuit may be made equal and opposite to that induced in the exciting winding 9. When starting the machine as a motor, the rotor runs up to a speed which is approximately one-half that which it would have if both rotor and stator were provided with threephase windings, and when the switch 13 is closed the machine pulls into step. In a modification, the stator polyphase winding'is connected in open delta, two of the phases being supplied with alternating current and the third phase being utilized as a continuous-current exciting winding.