GB388739A - Improvements in and relating to synchronous electric motors - Google Patents

Abstract

388,739. Motors. FERRANTI, Ltd. and HOLMES, W., Hollinwood, Lancashire. July 30, 1931, No. 21801. [Class 35.] Motors with unwound iron armatures; driving arrangements.-A synchronous motor comprises a stator and rotor having teeth or polar projections, a constant field system associated with the stator or rotor, and a cyclically varying field system, the rotor and stator teeth being so arranged that when both field systems are brought into action the rotor is caused to vibrate in tune with the cyclically varying field and synchronous rotation is initiated. Figs. 1 and 2 show two rotor discs x, y which are mounted on a common shaft and are associated with stator pole plates a, band c, d as described in Specification 379,383. Permanent polarity is given to the pole plates by a permanent magnet, or a continuous-current excited electromagnet. The stator and rotor teeth have the same pitch but the stator teeth are displaced so that complete magnetic alignment occurs only at A, Fig. 1. When alternating-current is supplied to the magnet - coil of the motor, torques are produced at B, C and D in the direction of the arrows during one half cycle and in the opposite direction during the other half cycle. No torques occur at A. In the construction shown, the anticlockwise torque on the discs is greater than the clockwise torque and the amplitude of the vibrations is greater than the tooth pitch so that the rotor rotates in the anticlockwise direction. The air-gap at A is made smaller than at other places so that the rotor will always stop in the position shown. The rotor and stator may have teeth of different pitch. A flywheel may be attached to the spindle by a spring of such a characteristic that a condition of resonance is produced when the spindle is oscillated at a frequency corresponding to the impressed alternating current. In a modification, Fig. 7, a permanent magnet u has staggered bifurcated arms and the air gaps at m, n are made smaller than at the other poles. The stator poles in this construction are formed on the edges of the cylinder and of the closing disc of a pot type electromagnet.