"k" factors for Medium Voltage Fuses?
"k" factors for Medium Voltage Fuses?
(OP)
Is there a "k' factor for MV fuses to allow increasing the rated KAIC for operating voltages lower than the rated voltage rated?
My co-worker is checking a design of fused 4.16 kV motor starters. Short circuit levels under some unusual conditions are very close to the fuse interrupting rating. A sales engineer from the MCC supplier thought there was a "k" factor for fuses similar to the old ANSI MV circuit breaker rating factor.
For breakers, the interrupting rating could be raised by the ratio of the rated voltage to operating voltage within the range of <k. (Constant MVA interrupting rating). Example: a 5.0 kV, 50 kA breaker operating at 4.16 kv, with k=1.2, could have an interrupting rating raised by 5.0/4.16 = 1.20 for a rating of 60 kA. That standard is no longer applicable for modern breakers that are current limited and not MVA limited.
I haven't found a similar standard for fuses in the manufacturers' literature. Is there one?
Thank you
My co-worker is checking a design of fused 4.16 kV motor starters. Short circuit levels under some unusual conditions are very close to the fuse interrupting rating. A sales engineer from the MCC supplier thought there was a "k" factor for fuses similar to the old ANSI MV circuit breaker rating factor.
For breakers, the interrupting rating could be raised by the ratio of the rated voltage to operating voltage within the range of <k. (Constant MVA interrupting rating). Example: a 5.0 kV, 50 kA breaker operating at 4.16 kv, with k=1.2, could have an interrupting rating raised by 5.0/4.16 = 1.20 for a rating of 60 kA. That standard is no longer applicable for modern breakers that are current limited and not MVA limited.
I haven't found a similar standard for fuses in the manufacturers' literature. Is there one?
Thank you






RE: "k" factors for Medium Voltage Fuses?
RE: "k" factors for Medium Voltage Fuses?
I think it would depend on the type of fuse and the mechanism used internally to interrupt the current and dissipate the resultant energy.
BTW, I am not suggesting trying this, I was just curious if it has been done.
RE: "k" factors for Medium Voltage Fuses?
Our solution is the usual: first check the calculations and data used in the short circuit study, add impedance if necessary to get a reasonable safety margin.
RE: "k" factors for Medium Voltage Fuses?