| 摘要 |
PURPOSE:To broaden the scope of protection in earth detection by arranging a load conductor crosswise to the incoming and outgoing direction of an electric equipment, by coating the load conductor and an insulating layer having an earth layer to a cable head and by arranging a directional zero-phase-sequence current transformer and a current transformer to the insulation layer. CONSTITUTION:When an insulation layer of a load cable 23 is deteriorated in insulation and is earthed, earth current iA flows to an earthing conductor 27 from an earthing point A through an earth metal layer 25, a crossover 28 and an earth terminal 26. The current is detected by a directional zero-phase- sequence current transformer 30 and a vacuum circuit breaker is interrupted so that the ground fault may be prevented from extending further. In case of an earth point B the earth current iB can be detected by the directional zero-phase-sequence current transformer 30 as the current flows to the earthing conductor 27 as in the case of earth current iA. The scope of protection in earth detection of an enclosed switchboard can thereby be broadened. |
