Protection of Hexagonal Phase Shifting Transformer

Phase Shifting Transformers (PSTs) are simple, reliable and economical means of controlling active power particularly if fast controls are not required for system stability. These transformers are built with unique connections of their windings, neither delta nor wye. Protection of such phase shifters is not well established. This paper presents original techniques for short-circuit protection of a hexagonal PST. Several novel protection schemes have been developed based on ampere-turn balance equations of a hexagonal PST. These schemes include linear and non-linear current based protection methods, a power based technique, and a phase comparison method. Protection schemes that require position of the tap changer for maximum sensitivity, as well as method working without this extra information are presented. The developed techniques have been validated with a digital and physical made-to-scale transformer models, and implemented on a general-purpose microprocessor-based relay platform.