| 摘要 |
The angle between the negative sequence and zero sequence currents for a power signal on a transmission line is measured and compared against a plurality of successive angle ranges from 0 DEG to 360 DEG . If the angle is 0 DEG +/-30 DEG , 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. An angle of 120 DEG +/-30 DEG indicates a BG fault, resulting in a second output blocking ground elements AG and CG and phase-to-phase elements AB and BC, while a phase angle of 240 DEG +/-30 DEG 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 are 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.
|
