| 摘要 |
PROBLEM TO BE SOLVED: To provide a directional ground fault protection relay, capable of preventing malfunctions by an oscillating voltage or a current that occurs in the zero-phase voltage V0 of a ungrounded distribution system after a failure was removed, when a directional ground fault is detected by comparing phase between the V0 and the zero-phase current I0 of a feeder. SOLUTION: A cycle decision part TC measures the cycle of zero-phase voltage V0 after the removal of a fault from a digital filter DF and an inhibiting part INH locks the output of the directional ground fault from a phase comparison part PC by the period, when the measured cycle is different from the base wave cycle of a distribution system. Changing the setting value in the direction of reducing the sensitivity of the phase comparison is included.
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