Three-phase transductor circuits for magnetic amplifiers

Various transductor connections for 3-phase operation are described; a 3-element circuit with separate self-excitation, and a 6-element circuit with auto-self-excitation, are selected for detailed examination. The modes of action of these circuits are described, the theoretical output-voltage/control-current characteristics are given, and expressions are obtained for the sensitivities and time-constants of the two arrangements. A comparison, theoretical and experimental, is made of the performances of these 3-phase circuits with those of equivalent single-phase connections. It is found that the change from single- to 3-phase connections does not usually result in improvement in performance, except that brought about by form-factor improvement, and therefore the principal reason for making such a change is to secure balanced loading of the supply where this is a 3-phase machine of relatively small output. The paper concludes with some comments on tests made on more than ten 3-phase connections as a guide to design work.