GB436145A - Improvements in and relating to synchronous electric motors - Google Patents

Abstract

436,145. Motors. FERRANTI, Ltd., and HOLMES, W., Hollinwood, Lancashire. March 6, 1934, Nos. 7147 and 27073. [Class 35] Motors with unwound iron armatures.- The stator of a self-starting synchronous motor has a set of pairs of pole elements f, g, associated with one end of the core b carrying the winding a and a further set of pairs of pole elements h, j associated with the other end of the core, pairs of pole elements on one set being interpolated between pairs of pole elements on the other set, and certain of the pole elements in each set being lagged as by conducting sleeves m, k; the rotor embodies a magnetizable member or members n of ring form having high magnetic retentivity in which poles are produced solely by the action of the stator field. The poles f, g are cut from the cup-shaped member d, e and the poles h, j from the plate c. In this form, the ends of the upper set of pole elements lie in the surface of a cylinder and the ends of the other pole elements lie in a plane normal to the rotor axis. In a modification both sets of pole elements form parts of cup-shaped plates and the lagging conductor is in the form of a set of identical copper plates perforated to receive the lagged pole elements f, h and notched to receive the unlagged elements g, j. In a further modification, Fig. 6, the poles f, g appertaining to the lower end of the core form parts of two separate cupshaped members s, t fitting one within the other and separated by a copper annulus u The poles h, j, form parts of two plates v, w separated by a copper annulus x. Some of the poles may be omitted. The rotor ring n which may have radial grooves to define the induced poles may be formed of tungsten steel, cobalt steel, aluminium alloy steel or cast steel. In order that the motor may have a good starting torque and also a good synchronous torque, two rotor rings may be fitted, one comprising material of high permeability such as cast steel, tungsten steel or chrome steel, and the other of high coercive force such as cobalt steel, nickel-aluminium steel or silver-manganese aluminium alloy, e.g. as described in Specification 406,086. Both rotor rings may be disposed together outside or inside the cylinder constituted by the ends of the stator poles, or one ring may be arranged inside and the other outside.