Relay device and corresponding method

A method of operating a relay device, in an electrical circuit comprising first and second main circuit breakers, and a bus tie circuit breaker connecting the first and second main circuit breakers, the method comprising computing a first positive sequence current phasor for the first main circuit breaker and a second positive sequence current phasor for the second main circuit breaker computing a first positive sequence voltage phasor for the first main circuit breaker and a second positive sequence voltage phasor for the second main circuit breaker; computing a correction of the first positive sequence voltage and second positive sequence voltage to a line-to-neutral phase angle reference if there is any rotation in a potential transformer connection; determining a fault has occurred when a magnitude of a current through at least one of the first main circuit breaker or the second main circuit breaker exceeds a predetermined threshold; determining a phase angle difference by comparing the phase angle of the positive sequence current phasor with the phase angle of the positive sequence voltage phasor for both the first main circuit breaker or the second main circuit breaker having the magnitude of current determined to have exceeded the predetermined level; and determining the fault is located upstream or downstream of the first main circuit breaker or the second main circuit breaker having the magnitude of current determined to have exceeded the predetermined level, if the phase angle difference is determined to be above a predetermined amount.