Creation of Positive and Zero Sequence Equivalent Circuit Models for Three-Winding Transformers

To calculate short circuit currents correctly and to make protection and coordination settings, it is important to measure the positive and zero sequence impedances of power transformers, which are indispensable elements of the power system. In this study, the measurements and mathematical operations performed to obtain the positive and zero sequence impedance models of three-phase transformers obtained from three-winding single-phase transformers are explained in detail. For the verification studies of the positive and zero sequence impedance equivalent circuit model of the single-phase 1 kVA, 276/120/54 V, mantel type, YNyn+d connection group test transformer, phase-ground fault was experimentally carried out in Kocaeli University Facility Research and Application Unit Laboratory. Model verification studies were supported by performing phase-ground fault in MATLAB/SIMULINK environment. Phase-ground fault solution was performed with symmetrical components by replacing the transformer equivalent circuit obtained from positive and zero sequence measurement results. The obtained equivalent circuit model was verified with simulation study and experimental measurements.