Influence of tertiary stabilizing windings on zero-sequence performance of three-phase three-legged YNynd transformers. Part I: Equivalent circuit models
A detailed analysis of the influence of the stabilizing winding on the zero-sequence behavior of three-phase three-legged YNynd transformers is presented. The analysis is based on a complete set of onsite zero-sequence measurements taken in three power transformers with different internal designs. Based on these measurements, the paper assesses the ability of various equivalent circuit models to reproduce zero-sequence performance accurately. Separate T-type zero-sequence equivalent circuits produce a complete and sufficiently accurate description of the zero-sequence behavior of YNynd transformers. These experimental data and results will be of great use in analysis of tank overheating hazard and short-circuit duty in three-phase three-legged YNynd power transformers.