GB682956A - Improvements in electric motors - Google Patents

Abstract

682,956. Dynamo - electric machines. BRITISH THOMSON-HOUSTON CO., Ltd., and LUDBROOK, L. C. March 29, 1950 [May 27, 1949], No. 14248/49. Class 35. A voltage proportional to the speed and direction of rotation of an A.C. or D.C. commutator motor is produced at the main or at auxiliary brushes by subjecting the rotor to a fixed auxiliary A.C. or D.C. field on the main or quadrature axis. In one form, Fig. 1, a D.C. motor having split series windings S1, S2, has an auxiliary quadrature exciting winding S4 which is D.C. excited to produce the speec dependent voltage at quadrature brushes X, Y In a modified arrangement for D.C. motors which avoids commutation difficulties, an A.C, auxiliary field is superimposed on the main field, the A.C. component of the output at the main brushes being filtered from the main D.C. voltage, and used in a demodulator as described in Specification 663,277, [Group XXXVIII], to produce a D.C. voltage depending on the motor speed. Alternatively, a condenser may be connected across the main brushes so that the resulting A.C. current produces an armaturereaction field which is picked up by a search coil in quadrature with the main field. In A.C. motors, the main field may have a different frequency superimposed on it or, as in Fig. 3, which shows a motor with split series field windings S1, S2, the main field may be biased by a fixed D.C. field S3. This field may conveniently be derived from the A.C. supply through a rectifier RB and smoothing circuit SC and S1C1. The continuous E.M.F. produced appears at auxiliary brushes X, Y, in quadrature with the main brushes of the machine, the supply frequency component induced by transformer action being balanced out by an auxiliary field winding S5 or by an external transformer fed from the main supply.