Patent GB-598289-A (GB)
Title: Improvements in and relating to dynamo electric machines
IPC: H02K47/16
Filed: 1942-09-21
Abstract: 598,289. Dynamo-electric machines; automatic control systems. MORRIS, D. G. O., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Sept. 21, 1942, No. 13305. [Classes 35 and 38 (iv)] To quicken the secondary current response to changes of the variator current of a metadyne machine the secondary compensating winding of the machine is shunted, wholly or in part, by an impedance, e.g. a resistance or choke, which during change of varia,tor current diverts a lagging current from the shunted portion of the compensating winding. The action of the shunt circuit is to reduce the angle of lag of the sinusoidal series of current components, into which the changing secondary current may be resolved, behind the corresponding components of the variator current which. cause the change in secondary current. The shunt circuit is preferably such that the phase advancement of the secondary components causes them to lead the corresponding components of the variator current. The machine is particularly adapted for use in automatic control systems of the kind wherein deviation of a controlled quantity from a predetermined value affects the variator excitation and in which the corresponding change in secondary current operates to produce a restoring effect on the controlled quantity, the improved transient response of the machine resulting in a reduction of the time lag, freedom from hunting and greater stability of the system. Fig. 1 shows a machine having a variator winding 2 and secondary brushes bd supplying current through a compensating winding 3 to a load 6, the compensating winding being shunted by a choke 7 and resistance 8. The shunt may extend only over a portion of the compensating winding as shown by the dotted line. In cases where it is desired to limit the voltage rise across the load 6, the shunt circuit may be arranged as shown in Fig. 2, so that the voltage across the load also appears across the shunt circuit. Instead of the shunt circuit being arranged directly across the secondary brushes it may be across a portion of the load and all or part of the compensating winding, and means may be provided for switching the shunt circuit from one side to the other of the load terminals. Fig. 3 shows another arrangement in which a further shunt circuit consisting of a choke 9 and a resistance 10 is connected across the secondary brushes of the machine. To prevent current flow in the shunt circuit under steady state conditions of secondary current a condenser may be arranged in the shunt circuit, but the resultant impedance of this circuit should be inductive. Alternatively, a motor 11, Fig. 4, having constant excitation may be arranged in the shunt circuit so that it provides a back E.M.F. opposing the voltage across the compensating winding and allows current to flow in the shunt circuit only under transient conditions. In a modification, auto transformer 17, connected as shown in Fig. 6, forms in conjunction with the resistance 8 the shunt circuit for the compensating winding 3. Specifications 539,837 and 592,209 are referred to.