Ground distance relay compensation in the presence of delta-hexagonal phase shifting transformer

In this study, the effects of the delta-hexagonal phase shifting transformers (PSTs) on the operation of distance relays and their trip boundaries are investigated under different fault resistances and locations. Existence of fault resistance in phase-to-ground faults creates an unreliable operation of distance relays. Trip boundaries are used to determine the fault resistance effects on the impedance calculated by the relay. Moreover, PSTs are used to control the power flow in transmission lines. Finally, a feasible method for eliminating the PSTs detrimental effects on the operation of the distance relays is presented. This method, which uses the voltage difference between the PST terminals, is getting prevalent in modifying the operation of the distance relays even under the high resistance faults. Phasor measurement units (PMUs) are used to calculate this voltage as PMU signals and a remote signal system is used to transmit them to the system protection centre. All the simulations are conducted with Electro-Magnetic Transient Program.