New algorithm for the protection of delta-hexagonal phase shifting transformer

Delta/hexagonal phase shifting transformer (PST) represents both magnetically coupled and electrically connected circuits, which makes it unique in design and construction from a standard transformer. Conventionally, differential protection serves as a main protection element of PST and offers distinguished features such as speed and selectivity. On the contrary, it is prone to various new challenges in addition to well-recognised traditional ones when applied to delta/hexagonal PST. New challenges include non-standard phase shift between two ends, saturation of the series winding, dependence of differential/restraining currents on tap changer position and turn-turn fault detection. This study exploits the unique design of PST and explores the suitability of applying electromagnetic equations by presenting a new algorithm for the protection of PST. In addition to the internal/external fault detection and discrimination capability, unlike differential protection, the proposed algorithm remains stable during magnetisation inrush current, current transformer saturation and saturation of the series winding. Even though the implementation of the proposed algorithm requires currents, voltages and tracking of the tap-changer position, capabilities of the algorithm make it a distinguished and unique protection solution. Performance of the algorithm is tested and analysed for various fault and non-faulted power system conditions using power systems computer aided design/electromagnetic transient including DC (PSCAD/EMTDC) software.