Experimental study of phase-angle controlled magnetic amplifier

Magnetic amplifiers can be rendered phase sensitive with the aid of phase-sensitive rectifiers [1]. In the present study phase sensitivity was effected directly, without recourse to an additional device with a phase-sensitive characteristic. It is shown that conventional two-core amplifiers, with one load winding and one control winding only on each core, are made phase sensitive by application of a phase-dependent ac rectified signal. Experiments were carried out with a signal derived from supply voltage for the load circuit and obtainable from any phase-shifting device (selsyn, resolver). In conjunction with the even-harmonic voltage produced at the control-coil terminals by the nonlinearity of the core characteristic, it results in phase-angle dependence of the even harmonic no-load voltage. Intrinsic feedback on the control side (and in certain cases feedback from the load circuit) gives the amplifier its phase-angle dependent current characteristic. If a pair of identical amplifiers are used with the control signal originating from different phases, zero current and phase reversal are obtainable at the output. Similarly, dc output with a directional characteristic is obtainable by transferring the load to the control circuit and connecting the load circuit of the two amplifiers to different phases of the supply source, the signal source being single-phase in this case. Load feedback, added to the intrinsic feedback of the control side, permits a current jump at a certain predetermined phase angle, so that the system operates like a switch; this jump can be reversed by opening the load feedback circuit. In the Appendix, an approximation is derived for the even-harmonic no-load voltage as function of the phase angle of the signal. This can be used as Thévenin voltage, and the calculation continued in the conventional way [2], [3].