GB429200A - Improved means of starting synchronous electric motors - Google Patents

Abstract

429,200. Synchronizing; controlling A.C. motors. ENGLISH ELECTRIC CO., Ltd., 28, Kingsway, London, and YOUNG, J. B., 11, Baswich Lane, Weeping Cross, Stafford. Dec. 16, 1933, No. 35415. [Class 38 (iv)] [See also Group XXXVII] A synchronous A.C. machine is started as a motor by first applying thereto a low A.C. voltage which is ahead of the normal running voltage by some predetermined phase difference and then disconnecting the machine from the low voltage source for such a time interval before connection to the normal supply as to allow the machine to become substantially in phase with the latter. Fig. 1 shows an arrangement in which a synchronous machine is started by connection through switch S2 to the low voltage tappings c, a, b, on three phase auto-transformer. The machine windings 1, 2, 3, are connected for running to the phases A, B and C respectively, the voltages of which lag 120‹ behind the voltages of the tapping points c, a, b to which these windings were previously connected. Fig. 3 shows an arrangement for starting up a synchronous machine under light load by the use of a three phase star connected transformer having two series connected windings wound on different limbs and connected in series between each terminal and the neutral point. The low starting voltage is obtained from tappings a, band c on the set of windings adjacent the neutral point, and the running voltage from the terminals A, B and C, while the phase angle between these voltages is varied by varying the ratio of the number of turns of the two series connected windings connected to each terminal. The value of the starting voltage may be varied by varying the positions of the tapping points. According to the Provisional Specification a leading voltage for starting may be produced by the use of an open delta connection on the tapped secondary of the main transformer.