Current limiting fuses
Current limiting fuses
(OP)
Under what circumstances will a current limiting fuses take longer than one half of a power frequency cycle to fully interrupt a short circuit current significantly greater than the current at which the fuse begins to current limit? Are there differing considerations for HV fuses versus LV fuses? The reason I ask is to try and rationalise the ANSI approach with the traditional British approach to grading relays upstream from current limiting fuses. ANSI permits a minimum time margin of 0.12 seconds whereas the British formula calls for a time margin not less than 40% of the fuse's melt time plus 0.15 seconds.





RE: Current limiting fuses
RE: Current limiting fuses
Z
RE: Current limiting fuses
Coordination between low voltage fuses is determined by test for the most part, especially in the current-limiting range. It gets complicated when there are multiple devices in series and all are trying to trip or melt. for lower values of fault current, the fuse minimum melt and total clearing time curves should be pretty accurate.
RE: Current limiting fuses
My concern is grading with an upstream relay.
RE: Current limiting fuses