| 摘要 |
The angle between the negative sequence and zero sequence currents for a power signal on a transmission lute is measured and compared against a plurality of successive angle ranges from 0.degree. to 360.degree.. If the angle is 0.degree. ~ 30.degree., an AG fault is indicated and a first section output is produced blocking ground elements BG and CG and phase-to-phase elements AB and CA. Art angle of 120.degree. ~ 30.degree. indicates a BG fault, resulting in a second output blocking ground elements AG and CG and phase-to-phase elements AB and CG, while a phase angle of 240.degree. ~ 30.degree. indicates, a CG fault, resulting in a third output blocking ground elements AG and BG and phase-to-phase elements BC and CA. If the phase angle is not covered by the above three primary ranges, then a second stage of comparisons arc made, including determining the magnitudes of the phase-to-phase distance elements, and then comparing the phase-to-phase resistance of the lowest of those with the apparent resistance of the one ground element, i.e, AG, BG or CG, associated with the non-primary (secondary) range of angles which includes the measured phase angle. If selected criteria are met, then an output is asserted to block the ground and phase-to-phase elements noted above associated with that ground element.
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