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.
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