A Double-Break Oil- or Gas-Blast Power Fuse

The use of two fuse elements of different rating, in series, in a high-voltage fuse device is described in this paper. The two elements are placed in a tube and the tube is filled with an arc-extinguishing substance and sealed; one end with an expellable plug. In operation the lower rated element melts first on an overcurrent and draws an arc; the energy from this arc is used to build up a pressure and forces the sealing plug out which establishes a second arc. Then the pressure in the tube blasts the arc extinguishing substance into the second arc and interrupts the circuit. For convenience, the circuit-interrupting part of the device is built in the form of a cartridge refill for insertion in a fuse tube or holder. Seven years of field experience have been obtained and is reported in this paper. The device has been applied on circuits up to 60kv.