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back-up fuse links are the closest inconstruction to LV cartridge types. However, a longer strip element with many more restrictions is necessary to produce the large number of series arcs needed to interrupt a high voltage. Fuse manufacturers achieve this by coiling the element around a ceramic core with a star shaped cross section. In this way, a 1m long element can be fitted into a 250mm long fuse body. If the adjacent coils are too close, there will be a flashover between them and this sets a practical limit on how long an element can be crammed into a particular cartridge, and how many elements can be used in parallel. Like an LV cartridge fuse link, an HV fuse link of thistype has a ceramic body.Many HV current limiting fuse links are also fitted witha

High Voltage - 12341 High Voltage Fuse Technology

Current LimitingFor the protection of equipment operating above 1000 volts AC

Current limiting HV fuse links split into threeinternationally recognised types: general purpose fuse links, which will interrupt allcurrents from rated breaking capacity down to a current that will melt the elements within one hour. A third type is the full range fuse. This term applies to fuse links that can interrupt any current below the rated breaking capacity that melts the fuse elements satisfactorily. Current limiting back-up (or partialrange ) fuse links, which will interrupt any currentfrom their rated breaking capacity down to a minimum breaking current specified by the manufacturer; and striker mechanism . This not only provides the userwith a visual indication that the fuse link has operated, but can also be used to operate other switchgear. In this way, a fuse on a single phase system can cut off all three phases if a fault occurs. Striker mechanisms are driven by explosive charges orcompressed springs. Both are triggered by a thin fuse wire running the length of the fuse, usually through the centre of the star shaped core. The wire is connected
Cross Section End capPorcelain barrel Fuse elementsGranular QuartzStriker coilExpelled striker Star coreMoisture tight seal Silver ceramicpoint contact Star coreStriker coil GranularQuartzFuse elementsPorcelain barrel in parallel with the elements, so a current flowsthrough it when the elements melt. The current heats up the wire and detonates the explosive charge, or melts the wire andreleases the spring, pushing the striker pin out of the fuse link’s end cap. A lock washer mechanism makes it impossible to push the pin back into the fuse body.There are several variations on this design for specificapplications. For example, the elements in three- phase motor protection fuse links are corrugated to withstand the cyclical mechanical stresses induced by the high starting and stopping currents drawn by the motor.
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