Calculation of two-phase short circuit current in electrical network when it is powered from the transformer with connection of windings according to the scheme $\mathrm{Y}/\Delta-11$

Abstract

Since when connecting the transformer windings according to the scheme $\mathbf{Y}/\boldsymbol{\Delta}-11$, the currents of direct and reverse sequences are equally transformed from one winding to another and the short-circuit resistance in the equivalent circuit for these currents and their sums are the same, if we neglect the magnetizing currents, the primary and secondary currents in each phase of the reduced transformer will be equal. This means that the currents and MDS of the primary and secondary windings are balanced in each phase separately and the influence of one phase on the other is absent. This gives the opportunity to calculate the currents of SC without conversion of the triangle into a star. In this case, the calculation is simplified and becomes more obvious. When determining the short-circuit resistance to the phase of the transformer with the connection of the windings Y/D, it is logically more reasonable and more clearly from a physical point of view to use a formula that includes not linear but phase voltages.