Abstract: Abstract:Aiming at the false trip accident of the 10kV line protection in an 110kV intelligent substation, the protection devices and the secondary circuit were inspected, and the site record files were analyzed. It was determined that the reason of the false trip accident is abnormity of the AC current sampling of the protection, and the reason of the abnormal AC current sampling is looseness of the AC plugin components, which causes floating voltage in circuit. At last, the relevant preventive measures were proposed.

Key words: Keywords:intelligent substation, line protection, false trip, AC current sampling, plugin component, floating voltage