GB528789A - Means for determining the rate of change of current in a d.c. electric circuit - Google Patents

Abstract

528,789. Control of D.C. motors. ENGLISH ELECTRIC CO., Ltd., FENEMORE, A. S., and SHAW, N. H. March 3, 1939, No. 7011. [Class 38 (iii)] Field control; varying E.M.F.-An inductive winding, for example the field winding of a motor 10 is energized from a D.C. source 6 and divided in two equal parts 1, 2, arranged as opposite alternate arms of a wheatstone bridge, the other arms of which comprise resistances 3, 4, each equal to the resistance of one of the field sections. Thus the time constant of the field circuit may be changed by the opening and closing of a switch 5 connecting the balanced diagonal points of the bridge. The ratio of the resistance 3 to the resistance of the field section 2 and also the ratio of the resistances of the other arms may differ from unity to give different degrees of adjustment of the time constant. Further adjustment may be obtained by means of a resistance in the supply to the field circuit or by a machine 7 driven with the supply generator 6 at constant speed and series excited by a winding 7a inducing a voltage on the machine opposing the supply voltage. A regulated separate excitation of the machine 7 is effected by a winding 7b. Further windings 7c, 7d on the machine 7 energized by the currents passing to the field sections 1, 2. may give an increased time constant to the circuit comprising the field 1, 2. The switch 5 may be operated by the controller for the motor 10, or by a polarized relay. The coil on each main pole of the motor 10 is divided into two parts included respectively in the winding sections 1, 2, or alternatively the N. pole windings may be grouped to form one section of winding and the S. pole the other. Specification 428,806 is referred to.