Drop-out fuse cutout and load switching fuse cutout are of outdoor used high voltage protective device. To be connecte with incoming-g feeder of distribution transformer of distributiong lines it mainly protect ratansformer or lines from short circuit and overload, and on/off loading current. Drop-out fuse cutout is composed of insulat insulator supports and fuse tube, static contacts is fixed on two sides of insulator suppor and moving contact is installed on two ends of fuse tube. Fuse tube is composed of inside arcextinguishing tube, outer phenolic compound paper tube or epoxy glass tube. Load switching fuse cutout probides enforedelastic auxiliary contacts and arc-extinguishing exclosure for switching on/off loading current.

At normally working via fuselink tightened the fuse tube is fixed to form up of close position. In case system occure faults, fault current result in fuse melt immediately and take place electric arc, which let arc-extinguishing tube being heated and explode a lot of gas. Th-is will produce high pressure and blow off the arc along with tube. After fuselink melt moving contact has no tightened strength again. Mechanism is locked and fuse tube drop out. Cutout now is in open position. When it needs to switch off during cutout loading, operat-or shall via insulating operating bar pull the moving contact, at its beginning main contact and auxiliary static contact is contacted st-ill. Whiling pulling the auxiliary contact is separated between auxiliary contacts there occur electric arc and the arc will be lengthene-ill. Whiling pulling the auxiliary contact is separated between auxiliary contacts there occur electric arc and the arc will be lengthene-d in arc-extinguishing enclosure gap and meanwhile arc-extinguishing explode gas to blow off the arc during current passing zero.