The Three-Circuit Transformer

Three electrical circuits which are separate and independent of each other, except that they are magnetically coupled by lines of force which interlink with the conductors in each circuit, can be represented by an equivalent circuit which has been developed from well-known fundamental equations. There are two distinct types of the three-circuit transformer which depend upon the relative directions of the fluxes flowing in the mutual paths in the magnetic circuit. Any arrangement of three coupled circuits will have the characteristics of either one type or the other. It is therefore important to study the magnetic circuits to determine the paths for the flux which interlink with the conductors in each of the electrical circuits. There are stray fluxes which interlink with the conductors in only one circuit and mutual fluxes which interlink with the conductors in two circuits. It may also be that there are mutual fluxes that interlink with the conductors in all three circuits. A problem of each type of transformer has been considered. In Case I the coils in each circuit, or the cores on which they are mounted, are disposed parallel to each other or arranged in the form of a Y in which case it is practically impossible to have a mutual flux thread through all three coils.