Analysis of a Shunt Phase-Shift Transformer for Multi-Generator Harmonic Elimination

A 12-pulse rectifier with the combination of Δ-Δ and Δ-Y type phase-shift transformers has been commonly used for harmonic cancellation in a large-scale power system. Recently a shut phase-shift transformer was suggested to have the same harmonic cancellation effect with more than 75% size reduction over the traditional phase-shift transformers provided that the power generation system equips with multi-generator that can be regulated with 30° phase difference between the two sources. Theoretically, the harmonic trapping performance of a shunt configuration is equivalent to 12-pulse rectifier with a significantly reduced transformer rating and size. However, the working condition and the performance of a shunt phase-shift transformer rectifier under the practical condition have not been verified. This paper presents a detailed analysis of a harmonic elimination principle of a shunt phase-shift transformer through an equivalent circuit model and a mathematical derivation. The analysis also describes the working condition for a shunt phase-shift transformer rectifier and the effect of phase difference of generators on the harmonic cancellation performance. The derived model is verified with computer simulation under the ideal and non-ideal 30° phase-differential configurations.