CALCULATION OF CURRENT DISTRIBUTION IN TRANSFORMER WINDINGS

The calculation of current distribution in the transformer windings is essential for calculation of the losses, temperature rises, short circuit stresses and so on. An important case is the calculation of the current distributon in a Y-∆ transformer in case of the line to line short circuit of ∆ side. Transformer with tertiary winding in YY∆ connection, with possibility of feed from both Y sids, is other interesting case. It is well known that the short circuit current in case of line to line short circuit is less than the three phase short circuit current. But the thermal stresses and the mechanical stresses in the windings of a Y- ∆ transfoermer in case of line to line short circuit is as high as the stresses in case of the symmetrical three phase short circuit. In this paper the current distribution in windings of a Y- ∆ transfoermer is calculated. In this calculation it is assumed that the sum of ampere-turns of windings on each leg of the core is zero. The line to line short circuit current distribution is then calculated explicitly. A general case for calculation of voltage and current distribution in transformer windings of any connection is then discussed.