A comparative performance analysis of three differential current measuring principles associated with phase shifting transformer protection

Various current differential based protection approaches are applied to detect and discriminate the internal/external faults in phase shifting transformer (PST). The differential current measuring principle is the one that distinguishes these approaches. These approaches exploit PST unique design to propose the differential current measuring principle that presents magnetically couple circuit, electrically connected circuit or compensated currents entering and leaving the zone of PST. In addition to the traditional challenges, PST brings new challenges to the biased differential protection. This paper presents a comparative performance analysis between various differential current measuring principles associated with PST. Old and new approaches are reviewed first followed by the detail performance analysis. Simulation studies are performed in the real time digital simulator (RTDS) and PSCAD/EMTDC. The results of the analysis identify the limitations of these approaches and suggest new research directions for the protection of non-standard transformers like PST.