A novel algorithm of calculating the circulating current on the delta side of three phase wye-delta connected transformer

The circulating current on the delta side of wye-delta connected three-phase power transformer is hard to measure. The differential transformer protection has to adopt current phase compensation method to compensate the circulating current. However, the differential current hardly reflect the magnetic exciting current of transformer no matter what kind of current phase compensation methods used. It limits many algorithms of identifying inrush current, such as the promising one based on the equivalent instantaneous inductance. How to obtain the circulating currents in delta side has become a difficult problem in transformer protection. In this paper, based on the voltage equations of transformer, the calculation of the resistance and leakage inductance of winding is deduced. And then, a novel algorithm of calculating the circulating currents in delta side is proposed Simulation results of MATLAB verify the accuracy of this algorithm, which offers a new way to calculate the differential currents exactly.