General

Drop-out fuse and load-drawing drop-out fuse are the outdoor high voltage protective devices. They are mounted on the high voltage side of distribution transformer or main or branch distribution circuits, to protect against short circuit and overload and make and break load current of transformer and circuit. Hereinto, drop-out fuse is made up of insulator support and fuse tube, its static contact is mounted at both ends of insulator support, and the moving contact is mounted at the both terminals of fuse tube that is composed of inner arc extinguishing tube and outer phenol aldehyde laminated paper tuber or epoxy glass cloth tube. The load-drawing drop-out fuse is provided with additional reinforced auxiliary contact and arc chute, which are used to make and break the load current.

When the drop-out fuse works normally, the fuse tube forms the closing position by using the tension of fuse wire. If the system has the trouble, the fault current will cause that the fuse is blown out rapidly, and bring electric arc, the arc extinguishing tube is heated for arc, to decompose much gas, and produce high pressure in the tube, then, longitudinally blown arc is formed along the pipeline, and the arc is extinguished for rapid lengthening. After the fuse wire is blown out, the lower moving contact misses the pulling force and turns downwards, the locking mechanism releases the fuse tube to make it drop out and form the obvious breaking position. When need to draw the load, the moving contact is drawn out with the insulating rod, at this moment, the main moving and static contacts still keep contact, if need the insulation, the contact is also drawn out with the insulating rod, meanwhile, the auxiliary contact separates, thus, electric arc presents among auxiliary contacts, and the electric arc is drawn out in the slit of arc chute, at the same time, the arc chute produces the gas, when the current crosses zero, the electric arc is extinguished.