Patent GB-622068-A (GB)
Title: Improvements relating to the control of a.c. commutator motors
IPC: G05F1/24
Filed: 1947-03-10
Abstract: 622,068. Induction regulators. SCHWARZ, B. March. 10, 1947, No. 6668. [Class 38 (ii)] [Also in Group XXXVII] An automatic control arrangement for an A.C. commutator motor comprises an induction regulator or other variable voltage transformer, having a secondary winding which is introduced into the rotor circuit of the commutator motor and produces a variable phase-shifting voltage which is dependent in magnitude on the adjustment of the induction regulator or other variable voltage transformer, such adjustment being made dependent on the interaction of at least two torques or forces, of which at least one is dependent on one or more of the load currents of the commutator motor. An A.C. commutator motor M has its stator winding ST connected to a supply MS and its commutator brushes B are supplied from the secondary windings S of a speed-regulating double induction regulator DIR, the primary windings, P, of which are connected to the supply. A single induction regulator SIR has its stator windings STC connected both to the supply and to a rotor winding RC, and is provided with secondary windings SC which are accom. modated in the same stator slots as the windings STC. The windings SC are connected in the rotor circuit of the motor M to provide, in addition to a leading compensating voltagecomponent, a load-responsive speed-regulating component therefor. The shaft SH of the induction regulator SIR is coupled to a unit RM, the fixed field winding FW of which is energized through a rectifier RE and a current transformer CT which is in circuit with the stator winding of the motor M. The armature of the unit RM is separately excited and its torque opposes the inherent torque of the induction regulator SIR. The induction regulator SIR is so adjusted that, under no-load conditions of the motor M, the secondary voltage of the winding SC has speed regulating effect only. Upon movement of the rotor of the induction regulator SIR from a predetermined position, the speed-regulating effect of the winding SC is retained and in addition there is injected into the rotor circuit of the motor a quadrature leading component which increases automatically with increasing motor rotor current. The inherent torque exerted by the induction regulator SIR upon the shaft SH increases with increasing displacement from the neutral position and also with increasing current in its windings, that is, with motor rotor current. This torque, tending to move the induction regulator back to its neutral position, is opposed by the torque of the unit RM, which is proportional to the stator current of the motor M. Stability of the rotor of the induction regulator SIR is obtained in such positions that the compensating voltages derived from the winding SC increase with increased motor load. If it is desired that the said compensating voltages be proportional to the motor load, an additional mechanical torque on the shaft SH is introduced through a lever L and a weight W, this mechanical torque assisting the inherent torque of the induction regulator SIR. The unit RM may have two field windings (Fig. 1c, not shown), dependent upon the stator and the rotor currents respectively of the motor M. The excitation of the unit RM may be arranged so that the compensating component introduced by the winding SC exceeds the reactive voltage drop. An additional voltage component, compensating for the ohmic voltage drop of the motor M, may be introduced into the motor rotor circuit through the winding SC, so providing a shunt motor characteristic. A compound characteristic may be similarly obtained. In a modification (Fig. 2, not shown) the induction regulator SIR is replaced by one of the normal type which is mechanically coupled to an A.C. torque motor, the stator winding of which is energized in accordance with the motor rotor current, and a mechanical torque device comprising a weight opposed by a spring. Compensating voltages of certain magnitudes may be introduced into the motor rotor circuit under no-load conditions. The motor speed range obtained by the regulator DIR may be shifted by introducing appropriate voltage-components into the motor-rotor circuit through the voltage-regulating arrangements. The armature current of the unit RM may be varied in accordance with the adjustment of the regulator DIR. A constant voltage may be introduced by transformer action into the motor-rotor circuit, to which the variable compensating voltage is added algebraically. The size of the compensating regulator may thereby be reduced and the range or variation of the resulting compensating voltage may be adjusted. According to the Provisional Specification, the system may comprise an induction regulator of the type described in Specification 549,536.