Patent GB-595660-A (GB)
Title: Improvements relating to inductive windings
IPC: H02P7/34
Filed: 1945-07-11
Abstract: 595,660. Control of D.C. motors. ENGLISH ELECTRIC CO., Ltd., and SHAW, N. H. July 11, 1945, No. 17683. [Class 38(iii)] [Also in Groups XXXV and XL] A direct current circuit containing inductive windings is arranged to have time constants which differ, at least under certain conditions, from the natural time constants of the inductive windings. A network comprises n parallel paths, each containing one of n equal sections of an inductive winding and each being completed by resistors to the total value of (n-1) times the resistance of each winding section; the network also comprises (n-1) rectifiers each connected in the same sense from an end of a winding section in one path to the beginning of a section in another. When currents flowing in the network are constant there is no voltage across any of the rectifiers. A bridge, connected according to the invention, comprises an inductive winding divided into two equal sections arranged as opposite arms, two resistors, each having resistance equal to one winding section, arranged as the two other opposite arms, and a rectifier connected between two opposite corners of the bridge. The invention is particularly applicable to the field windings of dynamo-electric machines, to cause the rate of change of field current with increase of applied voltage to differ from that on a decrease of voltage. When the field windings of a direct current motor are connected as the inductive windings of an abovedescribed bridge and an exciter supplies the two corners of the bridge which are not connected to the rectifier, an extra exciter field winding is connected across the rectifier in which is produced a transient current whereby there is injected in the supply a transient voltage further reducing the effective time constant. In a Ward-Leonard control system a direct current motor 1 is supplied from a generator 2 the field winding 21 of which is supplied from an exciter 3. The field winding of the motor 1 is divided into equal sections 11 and 12 arranged as opposite arms of a bridge, the other two arms which consist of resistors 13 and 14 which are each of equal resistance to a winding section. Terminals A and B of the bridge are supplied from an exciter 4 in series with an exciter 5. A rectifier 85 is connected across opposite terminals C, D, of the bridge. When the currents in the bridge are constant there is no voltage across the rectifier. When the currents in the bridge from A to B are increasing the inductance of the winding sections 11 and 12 limits the rate of rise of current therethrough and a current flows through the rectifier from D to C. The time constants of the windings are therefore substantially the same as if connected in series. When the currents through the bridge decrease the potential at C rises above that at D and the rectifier is non-conductive. The effective time constants of the windings are thus reduced. In a modification, the field windings of each machine 1 and 2 are divided into two equal sections 11, 12 and 34, 35, each pair being arranged as opposite arms of a bridge, completed by resistors 13, 14 and 36, 37 of resistance equal to that of a winding section. An exciter 3 supplies the terminals E and F of the generator field bridge so that with steady current conditions the bridge is balanced. When a potentiometer 25 is adjusted to change the generator field excitation the bridge becomes unbalanced and a current is passed through the exciter field 38 to accelerate the change of excitation. The bucking exciter 5 has a field winding 41 connected so that the bucking-effect is increased when the currents in the windings 11 and 12 decrease. The rectifier 85 passes current when the currents in the windings 11 and 12 increase to shunt the field winding 41. The motor may be quickly accelerated by rapid decrease of field strength, and when the motor field is strengthened for regenerative braking the rise of current is not excessive. Specifications 528,789, 594,951 and 595,665 are referred to.