Patent ID: 7345488

Claim:
An apparatus for determining a faulted phase resulting from a fault in a three-phase ungrounded power system, the apparatus comprising: a means for deriving a plurality of digitized signal samples from a corresponding plurality of measured signals of the three-phase ungrounded power system; and a microcontroller operatively coupled to the means for deriving, the microcontroller having a microprocessor and a memory operatively coupled to the microprocessor, the microcontroller being programmed to: calculate a magnitude and phase angle of a fixed reference phasor, determine an operating phasor, calculate a magnitude and phase angle of the operating phasor based on at least one of the plurality of digitized signal samples, compute a phase angle difference between the operating phasor and the fixed reference phasor, and compare the phase angle difference to at least one threshold to determine the faulted phase.