| 摘要 |
<P>PROBLEM TO BE SOLVED: To easily and accurately detect minute ground fault by only a zero-phase current value while preventing erroneous detection of the minute ground fault caused by an opening/closing surge, noise, etc. <P>SOLUTION: A zero-phase current detector is mounted in a live-line state to the distribution line where the minute ground fault is generated, and determination is made whether or not a first wave serge of the zero-phase current detected by the zero-phase current detector exceeds a first set value, which is larger than the opening/closing serge, and when the first wave surge of the zero-phase current exceeds the first set value, the minute ground fault is determined. When the first wave surge of the zero-phase current is in the state not exceeded the first set value, the determination is made whether or not it exceeds the second set value, which is smaller than the first set value, and when the first wave surge of the zero-phase current exceeds the second set value, the determination is made whether or not on and after the second wave of the zero-phase current exceeds a third set value, which is smaller than the second set value, periodically over the prescribed time or longer, and when on and after the second wave of the zero-phase current exceeds the third set value periodically over the prescribed time or longer, the minute ground fault is determined. <P>COPYRIGHT: (C)2013,JPO&INPIT |
