Parallel Operation of Transformers Whose Ratios of Transformation are Unequal

An equation is developed for use in meeting emergency conditions which necessitate the paralleling of transformer banks whose impedances expressed in percentage form are not equal. This equation makes it possible to calculate what change should be made in the ratio of transformation of the bank with the lower percentage impedance in order to prevent its being overloaded when the total load approaches the combined capacity of the two banks. It is pointed out that such an expedient is a makeshift justifiable only when maintenance of service is the paramount consideration and efficiency is, for the time being, of secondary importance. When conditions arise which do justify such a temporary arrangements ment, the method developed in the present paper affords a simple, yet accurate, means of solving the problem.