| 摘要 |
PROBLEM TO BE SOLVED: To easily detect a ground-fault excessive voltage of a three-phase AC wiring, and to simplify the work for the detection. SOLUTION: Three pieces of distribution cables 21, 22 and 23 of a three-phase AC wiring are covered with conductive materials 24, 25 and 26 in an electrically insulated state. The conductive materials 24, 25 and 26 are connected to a connection terminal box 28 with a common connection wire 27. A voltage- measuring unit 31 of a ground excessive-voltage relay 30 measures a voltage between the connection terminal box 28 and the ground. A voltage through a filter 32 detected by the voltage-measuring unit 31 is decided by a decision unit 33 based on a settled reference value of a settling section 34 and, when the occurrence of the ground-fault excessive voltage is determined, a power system from a commercial power source is cut off from a private wiring and the like. Thereby, the same function as of a usual zero-phase potential device can be obtained by a simple work of covering the distribution cables 21, 22 and 23 with the conductive materials 24, 25 and 26.
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