| 摘要 |
PROBLEM TO BE SOLVED: To provide a device which discriminates and informs the change of a system, such as disconnection, etc., caused by fallen snow when the ground capacitance of the system changes by automatically optimizing the operating point of the relay without performing any artificial ground-fault test. SOLUTION: Impedances R for measurement are connected to the tertiary side of a grounding transformer 7 by switching and the ground capacitance C of a three-phase batch system is calculated from the then appearing phase angle changeϕn2 of the tertiary voltage of the transformer 7. Then the operating voltages V0 of ground-fault relays 20 and 21 are calculated based on the calculated ground capacitance C, system voltage E, and a ground-fault resistance value Rg which becomes a detection criterion and the relays 20 and 21 are automatically set at the voltage V0 . AnωC measurement control section 23 which automatically executes the series of above-mentioned operations at set timing is provided. In addition, anωC change detecting section 19 which generates a system change informing signal when the rate of change of the measured value of the ground capacitance C from the preceding measured value exceeds a reference value is provided.
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