Importance

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Abstract

For interrupting all values of electric current in a high voltage circuit which cause operation of a fuse within one hour, a plurality of parallel connected helically configured fusible elements formed of cadmium are embedded within quartz sand in granular form disposed within a housing structure which includes a tubular member of insulating material to the ends of which terminal caps are secured and connected to the ends of the fusible elements respectively so that currents of a high order of magnitude are interrupted in a fraction of a half cycle in a current limiting fashion and so that currents of a low order of magnitude and which are slightly in excess of normal rated load current of the fuse cause the temperature of the fusible elements to rise to the melting point within a longer predetermined period of time and then to establish a gap sufficient to withstand the recovery voltage. For substantially preventing degradation processes in the cadmium fusible elements, a non-porous metallic coating of substantially uniform thickness between 0.5 and 10 microns is arranged to cover each fusible element and wherein there is substantially no inter-metallic diffusion through the interface between the cadmium fusible elements and their metallic coatings at temperatures below the melting temperature of cadmium.

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First Claim