Abstract: A motor control circuit comprises first, second and third saturable reactors connected between three supply lines and the three phases of a motor. The reactors can be excited to energize the motor to give a high torque output in a forward direction. Two further reactors ("reverse" reactors) are connected between the second and third supply lines and the third and second motors phases.In the "forward" condition, the "reverse" reactors are unexcited and have line voltage across them. To drive the motor in the reverse direction at a lower torque level, the first reactor and the "reverse" reactors are excited at a lower level and the second and third reactors are unexcited. However, the latter two reactors are made to operate at a point above the magnetization curve knee point by passing current through them up to their full-load current, and they are thereby "stretched" across a voltage only slightly (say 13%) above the phase voltage. Hence, only the fourth and fifth reactors have to withstand full line voltage.

Abstract: In order to prevent pulses induced in the excitation winding of a saturable reactor due to load current in the main winding from causing partial demagnetization of the core, a compensating coil of the same number of turns as the excitation winding is mounted on the core to generate pulses equal and opposite to the induced pulses. The compensating coil pulses are applied across an inductor connected in series with the main winding. A diode in series with the compensating coil prevents the excitation current from flowing through the coil.

Abstract: A control circuit comprises two series-connected pairs of saturable reactors, the two pairs being connected in parallel between a supply line and a load. Between one pair of reactors are connected two back-to-back diodes, the center tap of which is connected to the common point of the other pair of reactors. The difference between the voltages across the reactor main windings causes feedback which increases the magnetization of the cores and reduces further the impedance of the low impedance windings.