
78 7 ◊ Transformers and Reactors
if P to S1 = X, P to S2 = X, S1 to S2 = Y
then, A + B = X, A + C = X, B + C = Y
and A = X – Y/2, B = Y/2, C = Y/2
If the secondaries are tightly coupled, then Y is very low, and the
equivalent reactance is nearly all in the primary. If they are poorly
coupled so that Y is high, the primary reactance, A, may go negative.
If the secondaries have a particular coupling to each other, the primary
reactance can be zero, and all the equivalent reactance is in the sec-
ondaries. A negative primary reactance implies a regulation character-
istic in which the secondary voltage of a converter falls less under
load, and this can be ...