On the efficiency of power transformers with «star-zig-zag with zero» winding connection scheme in rural electricity networks supplying household consumers

Abstract

The dependencies of the loss coefficient on the value of reverse- and zero-sequence current unbalance coefficients are obtained, allowing estimating the energy efficiency of power transformers operation at different unbalance characteristics. The electricity losses were calculated from these dependencies and from data obtained from instrumental measurements at rural substations supplying household consumers. It was obtained that the power transformer with «the star-zigzag with zero» scheme is 6 times more energy efficient than the power transformer with «the star–star with zero» scheme. However, with small values of the currents asymmetry (for five cases studied), the power transformer with «the star-zigzag with zero» scheme has overestimated power losses.