| 摘要 |
PURPOSE:To surely detect snapping, by using a low-cut filter to detect the current flowing through a distribution line and by extracting only the arc current component from the detected current. CONSTITUTION:The currents flowing through distribution lines 1 are detected by current transformers 31-33 provided on the power-source-side ends of the distribution lines so that the detected currents are applied to the differentiators 51-53 of a snapping detector 4. The differentiators constitute low-cut filters to extract high-frequency pulsating arc current components B superposed on load currents of AC power frequency. Overcurrent detecting circuits 61-63, which have reverse- timing property, act in response to the arc current components B. Since the circuits 61-63 have a slower melting-off property than the slowest melting-off property of several kinds lf insulated wires used for a distribution system and have a faster arc disappearing property than the fastest disappearing property of the insulated wires, the circuits 61-63 can be completely cut off. The detected signal is produced in a time range before the disappearance of arc and caused to cooperate with a ground fault detecting signal obtained from a ground fault relay. As a result, snapping can be surely detected. |
