High voltage fuse for interrupting a wide range of currents and especially suited for low current interruption

A high voltage fuse for interrupting a wide range of currents and especially suited for low current interruption having a tubular insulating casing, and an inert granular material of high dielectric strength within said casing, said fuse further comprising:

• one or more ribbon-type fuse elements, the elements being electrically connected in parallel when more than one is present;
• said one or more fuse elements comprising at spaced locations along the length of an element a first and a second plurality of portions of first and second predetermined reduced transverse cross-sections, respectively, of the fuse element available for the conduction of current, said second plurality of reduced cross-section portions having two or more parallel conductive segments;
• said first predetermined reduced cross-section portions having a fusible time-current characteristic so as to initiate melting before the second predetermined reduced cross-section portion under first abnormal current conditions in which the current applied to the fuse element exceeds a first predetermined current value for a first predetermined time duration;
• said second predetermined reduced cross-section portions having a fusible time-current characteristic so as to initiate melting before the first predetermined reduced cross-section portions under second abnormal current conditions in which the current applied to the fusible element is less than the first predetermined current and has a time duration exceeding a second value which is greater than the first predetermined time duration;
• said two or more conductive segments having fusible materials one of which has a higher melting temperature than the material of said remaining segment or segments so that said one conductive segment melts after the other segment or segments under said second abnormal current conditions;
• said one segment of each of said second plurality of reduced cross-section portions having a sufficiently long melting time under said second abnormal current conditions to force all of said remaining segments of substantially all of the second plurality of reduced cross-section portions to melt before melting of said one segments.