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Rectifier fuses

Rectifier fuses

Rectifier fuses

(OP)
It may seem obvious that a rectifier fuse is used with rectifiers.  But why?  It seems that the curves for rectifier fuses are very similar to "one-time" fuses.  We have a PT setup which was designed using old KAW type fuses, and they are labeled "rectifier fuse".  What makes a fuse a recitifier fuse?

RE: Rectifier fuses

I think one of the criteria for a semi-conductor fuse (assuming this is the same as a "rectifier" fuse) is that they create a low arc voltage during interruption. This reduces the voltage stresses on the semi-conductors.

RE: Rectifier fuses

(OP)
Figured it had something to do with transients uniquely harmful to semiconductors, but couldn't figure out which ones.

Thinking about it, that does make some sense.  Thanks for your info, GordS!!!

RE: Rectifier fuses

(OP)
Additionally... any idea why rectifiers fuses were desgined into a PT circuit?  They weren't used just cause they were lying around and handy.  For some reason they were designed into the project.

RE: Rectifier fuses

Seems that historically there has always been a race between the fuse and the junction it was protecting, and the fuse had a good chance of loosing.  On a PT application, wouldn’t inrush be in conflict with the speed of semiconductor fuses?  Are the KAWs significantly oversized?

http://www.bussmann.com/library/docs/Spd.pdf ‘high speed fuse application’ has some general information.  

RE: Rectifier fuses

(OP)
I don't know.  I just started working at this utility, but have heard of problems with the KAWs blowing out for apparently no reason.  As they pop, we replace them with other types, mainly KTK-Rs.  So that may have been the problem.  I just started looking at the problem yesterday and figured this could be a good place to get a jump start.

RE: Rectifier fuses

(OP)
I suppose the difference, then, is how the fuse interrupts rather than the time-current curve characteristics.  I think that they've been undersized at 5A.  We think lightning has been popping the KAW fuses and the KTKs are much more tolerant for lightning transients.

Thanks.

RE: Rectifier fuses

If you do need time delay for inrush, consider something like a Bussmann FNQ-R.  It's a time-delay fuse intended for inductive applications.
http://www.bussmann.com/library/bifs/1014.pdf
Shawmut lists ATDR as their equivalent.

RE: Rectifier fuses

Well, now I have it from two independent sources.  I was discussing that same fuse with someone else about 5 minutes ago.  Thanks, Busbar.

RE: Rectifier fuses

The big difference for semi-conductor fuses is the energy let through.  Typically a semiconductor fuse has a lower peak let-thru and lower I^2t.  The semicon fuses may have been used to try and minimize damage to the PT's during a fault.  Normally semi-conductor fuses are used at less than 1200V, what are they installed on?

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