Self-saturation in magnetic amplifiers

SATURABLE reactors, in their simpler forms, have been used in controlling many types of equipment. As is known, control is effected by adjustment of the reactor impedance with d-c premagnetization. The a-c windings are so connected that no fundamental component of power-frequency voltage appears in the d-c control winding. For optimum utilization of the core structure, the control winding must supply premagnetization equal to the sum of the magnetomotive force of the a-c windings and the magnetomotive force necessary to saturate the core. Generally, the control winding consists of many turns of fine wire. As a result, a high voltage can be induced in the control winding if one a-c coil becomes inoperative and the effective inductance and time delay of the control circuit are substantial. However, these factors can be reduced if feedback is used to equilibrate the magnetomotive force of the a-c windings so that the control winding need supply only the magnetomotive force required to saturate the core. Consequently, saturable reactors with feedback, or magnetic amplifiers, have been applied in many cases where simple saturable reactors would have been unsuitable.