High-voltage fuse behaviour with varistor commutation

Expulsion fuse operation using parallel connected ZnO varistors for current commutation offers new protection opportunities for this simple switching element. The advantages of low cost and full-range protection can be retained with the addition of current limitation and hence almost unlimited breaking capacity. Pad-mounted and cubicle applications may also be possible. The relations among varistor voltage, fuse element cross-section, fault current, circuit conditions and energy dissipated during current breaking operation have been analysed. It has been found that maximum energy dissipated by a fuse-varistor arrangement depends on the fuse element cross-section and the varistor voltage; these parameters play crucial roles in fuse dimensioning