Patent GB-616301-A (GB)
Title: Improvements in or relating to systems for controlling the supply of power to load devices, for example, electric motors
IPC: H02P23/00
Filed: 1946-05-14
Abstract: 616,301. Changing wave-shape; switching control systems. WESTERN ELECTRIC CO., Inc. May 14, 1946, No. 14549. Convention date, May 16, 1945. [Classes 38 (ii) and 38 (iv)] [Also in Group XXXVII] An electrical circuit controls the supply of power to a load device which is supplied through a circuit extending serially over the armature contacts of two relays, power being supplied to the load device only when each of the relays is in a pre-determined condition, a biassing direct current is applied to windings of the two relays and a cyclically varying current is also applied to windings of these to cause the relays to operate and release during each cycle of the cyclically varying current, and means is provided for varying the relative values of the biassing current and the cyclically varying current in the two relays for controlling the relationship between the operated periods of the two relays and thus the pulses of power supplied to the load device. When the windings of relays A and B, Fig. 1, are energized solely from a battery B1 and similar A.C. sources AC1 and AC2, the relays operate and release simultaneously and a load device 3 receives no power from a source E. When the directcurrent energization of one relay winding is increased and that of the other winding is decreased, for example by interpositioning the batteries B2 and B3, the relays no longer operate in unison and an intermittent current passes from the source to the load. In a control system, Fig. 3, for a separately-excited D.C. motor 24 the windings of relays A and B are connected in the anode circuits of a doubletriode thermionic valve AMP, anodes 16 and 17 being connected through the relay windings to a positive D.C. source, and cathodes 18 and 19 being respectively interconnected to an A.C. source and earth through resistors 20 and 21. If a D.C. signal is applied across terminals 10 and 11 to grids 12 and 13, a balanced condition of both units of the valve AMP, wherein the relays A and B operate in unison, is upset and the D.C. components supplied to the relay windings respectively increase and decrease, so that the relays no longer operate in unison and a pulsating current is fed from the source E to the motor armature. The pulses supplied to the motor armature are of duration proportional to the magnitude of the control signal and the direction of motor rotation is dependent upon the polarity of the control signal. A series split-field D.C. motor, a two-phase induction motor, and a split-phase motor, may be similarly controlled, (Figs. 4, 5, and 6, not shown). In the system of Fig. 5 one stator phase winding is supplied from a constant A.C. source, and the other from a separate A.C. source through the contacts of the two relays. Each relay has a low resistance winding supplied with constant A.C., and a high resistance winding which is connected to the anode circuit of the valve amplifier the grid potential of which is dependent upon a D.C. control signal. In the modification shown in Fig. 2, the battery B2 and one of the sources AC1 or AC2 have reversed polarity compared with the arrangement shown in Fig. 1. The connections from the source E to the contacts of the relay A are also reversed. In this system the contacts of the relays open and close alternately when there is no signal voltage, current pulses being fed to the load when both relays are in the front or back positions. A two-phase induction motor (see Fig. 7), a split phase motor, or a D.C. motor may be controlled according to this arrangement. As shown in Fig. 10, the relay windings A and B are each energized from a battery B1 and synchronous A.C. sources AC1 and AC2, the output of a third A.C. source AC3, which is variable in accordance with a control signal, being impressed on the two relay windings. Variation of the control signal varies the relative phase of the alternating-currents in the two relays and causes current-pulses to be supplied to the stator winding 64 of a two-phase induction motor, these pulses being alternately in opposite directions. A motor stator winding 65 is supplied with constant alternating-current in synchronism with the sources AC1 and AC2 and therefore in quadrature with the pulses in the winding 64. A direct-current motor (Fig. 11, not shown) may be similarly controlled by connecting the ends of its split field windings to the front contacts of the relays A and B and supplying the motor armature, through the moving contacts of the relays, from an A.C. source in quadrature with the alternating- current driving the relay A. Specification 616,302 is referred to.