Ratings of Fused Cutouts for Medium Voltage Distribution

[kartracer087]

Hello,

Just curious, does anyone apply fusible link style cutouts to their system by using the single-shot ratings? I believe the manufacturer's standard label is for a 5-shot operation at a given fault current (there are a series of tests in the IEEE standard). I know that some manufacturers have tested cutouts in a single shot rating, which essentially requires replacement of the fuse tube and the link after an operation. An example is for a 27kV cutout, a typical rating is 12,000A asymmetrical for the standard 5-shot, and 16,000A asymmetrical for single shot. Just curious if anyone applies this to their system. One of the issues is if you are borderline near the substation if it makes more sense to buy a power fuse which is much more expensive, or if relying on single shot ratings is sufficient.

 

[dpc]

Are you talking about the fuse clearing five downstream faults? Or five operations by an upstream recloser?

 

[davidbeach]

I’m guessing that the tube is good for 5 links vs. good for 1 link.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[kartracer087]

Yes, that is what I mean. Basically replacing the tube and link after one operation. Some manufacturers offer extended ratings for this although I'm not sure it's really a good practice or not. As I understand cutouts have to pass a number of tests and I believe at least three are high current interrupting tests and require replacement of only the link in the fuse holder per ANSI C37.41 for those three tests. So if a cutout carries a single shot rating then it becomes a manufacturer certified test not covered in C37.41. Was primarily curious as there may be reason to use this rating if you are borderline right at the interrupting limit near the substation. It also leads me to believe that cutouts actually have the capability of interrupting higher fault currents especially if the tube is replaced at each operation.

 

[stevenal]

If the tube appears damaged it is replaced.