Transformer Modeling for Three-Phase Distribution Network Analysis

This paper presents a symmetrical components approach for computing the phase-coordinates nodal admittance matrices of three-phase transformers, where each connection is comprised either of three single-phase units or one three-phase unit. The approach is based on assembling the symmetrical component circuits into the different three-phase connections; it can straightforwardly handle unsymmetrical transformer banks with different phase electrical characteristics or missing phases, and grounding impedances. The proposed approach easily accounts for the various clock numbers quoted in the British Standard (BS) and the International Electrotechnical Commission (IEC) Standard on power transformers; this presents an advantage as compared to classical phase-coordinates approaches that require defining a distinct connection matrix corresponding to each transformer vector group.