Self-healing fuse development

The self-healing fuse is a very fast acting current overload protective device which opens and recloses in a few milliseconds. The fuse confines a mercury column in an insulated channel and returns the mercury to the channel after firing. Ratings 5 to 50 amperes at 600 peak volts are possible with a life of hundreds of cycles. Compared to conventional fuses, much less fault current energy fires the fuse by heating the mercury to boiling temperature. Next an arc discharge develops while explosive forces expel the liquid mercury from the channel. Then the high impedance arc either extinguishes immediately, or operates for a few milliseconds, until a switch opens the circuit. Containing this explosion and arc demands a reinforced, very refractory insulator as a fuse channel. Several channel materials and geometries have been tried. Preferred are sapphire and beryllia as materials and several cylindrical holes in parallel as a geometry.