E fuses & harmonics

[SG-1]

Has anyone heard of harmonics causing a medium voltage "E" fuse in the 1-5 amp range to have a catastrophic failure ( blown in half ). The two halves look like a laser beam hit them in places. The fuse sits right on top of an epoxy cast CPT (5kva), so it is directly exposed to the heat generated by the transformer. The CPT & fuses are drawer mounted. The transformer looks fine except for the scorch left by the fuse when it ruptured & the windings are intact enough pass a polarity test. It will be scrapped later. The insulation on the transformer lead that connected to the fuse shows thermal damage on the first 3 inches where it was connect to the fuse.

I have known transformers to fail because of harmonics, but never heard of any fuses.

 

[brian john]

I have seen fuses fail as you describe from a thermal condition, the fuse clip is loose fuse heats up and burns open, looks like an explosion but in reality it was more of a burn out.

 

[zog]

Has anyone heard of harmonics causing a medium voltage "E" fuse in the 1-5 amp range to have a catastrophic failure ( blown in half ). The two halves look like a laser beam hit them in places. .

Come on now, you can't post that without photos

 

[SG-1]

Come on now, you can't post that without photos

Is that a new 2013 forum rule ?

 

[SG-1]

I have seen fuses fail as you describe from a thermal condition, the fuse clip is loose fuse heats up and burns open, looks like an explosion but in reality it was more of a burn out.

That fuse does have a crappy connector at the end where the HV lead from the transformer is connected & a lot of heat was concentrated there. The blow out was toward the other end. Thanks, that opens a new & more likely avenue for the failure.

 

[zog]

Is that a new 2013 forum rule ?

Yes, anytime "blow up" or "laser beam" is used in a post photos must be posted.

 

[SG-1]

Ok, I do not want to break any new rules.

 

[robbietan]

Has anyone heard of harmonics causing a medium voltage "E" fuse in the 1-5 amp range to have a catastrophic failure ( blown in half ). The two halves look like a laser beam hit them in places. The fuse sits right on top of an epoxy cast CPT (5kva), so it is directly exposed to the heat generated by the transformer. The CPT & fuses are drawer mounted. The transformer looks fine except for the scorch left by the fuse when it ruptured & the windings are intact enough pass a polarity test. It will be scrapped later. The insulation on the transformer lead that connected to the fuse shows thermal damage on the first 3 inches where it was connect to the fuse.

I have known transformers to fail because of harmonics, but never heard of any fuses.

Ten years in a distribution company poco and have asked around older colleagues - no one has heard of an instance

 

[SG-1]

Ten years in a distribution company poco and have asked around older colleagues - no one has heard of an instance

Thanks for the reply. I appreciate the input. There were people trying blame the failure on harmonics. All the evidence points to a loose connection at the transformer end of the fuse.. Brian got me looking in the right direction. I think we are still waiting for a report back from the fuse manufacturer.

 

[zog]

Thanks for the reply. I appreciate the input. There were people trying blame the failure on harmonics. All the evidence points to a loose connection at the transformer end of the fuse.. Brian got me looking in the right direction. I think we are still waiting for a report back from the fuse manufacturer.

Thanks for the pic, never seen anything like that either but will send to my fuse God buddy, he know more about fuses than anyone should.

 

[brian john]

I have seen this before and that looks like a thermal issue, overheated at the ferrule.

 

[SG-1]

I have seen this before and that looks like a thermal issue, overheated at the ferrule.

I agree Brian, here is a good view of the ferrule connection. The other ferrule pretty much looks normal. Note the heat that must have been present to cook the silicone insulated conductor.

 

[rcwilson]

I 've seen 480V fuses blow like that. They were rated 5 kAIC but applied in an MCC with about 37 kA fault current. Blew open and burned the complete bucket. But I've never seen that happen with MV fuses.

Could the system short circuit level also be too high? In some switchgear and generator applications a series resistor is used to drop the short circuit current down to the VT fuse rating. The VT draws so little current during operation that the resistor has no effect on the VT accuracy. Maybe this application needs a current limiting resistor.

But I would bet it is due to the overheating of the connection as so well diagnosed by others.

Thanks for complying with our new "rules". Those are neat pictures!

 

[SG-1]

I 've seen 480V fuses blow like that. They were rated 5 kAIC but applied in an MCC with about 37 kA fault current. Blew open and burned the complete bucket. But I've never seen that happen with MV fuses.

Could the system short circuit level also be too high? In some switchgear and generator applications a series resistor is used to drop the short circuit current down to the VT fuse rating. The VT draws so little current during operation that the resistor has no effect on the VT accuracy. Maybe this application needs a current limiting resistor.

But I would bet it is due to the overheating of the connection as so well diagnosed by others.

Thanks for complying with our new "rules". Those are neat pictures!

Mr. Wilson, that was my first thought as well, but the CPT seems to be working order, passed polarity, dielectric on both primary & secondary, & turns ratio.

 

[zog]

My fuse guy says that is a type of failure seen when the ribbion element that is used as the current limiting portion of the fuse fails. The ribbon has holes in it and can weaken from small overcurrents (Inrush for example) or external heating. So it is very possible there was no real fault, just the loose connections producing heat, weakening the ribbon and leading to a failure.

 

[Electric-Light]

Thanks for the pic, never seen anything like that either but will send to my fuse God buddy, he know more about fuses than anyone should.

Overloads scorch and melts, but vaporized metal is usually a result of a short circuit. If the fuse holder normally only carries a few amps, and fault current places thousands of amps, that weak link can certainly vaporize.

 

[brian john]

Overloads scorch and melts, but vaporized metal is usually a result of a short circuit. If the fuse holder normally only carries a few amps, and fault current places thousands of amps, that weak link can certainly vaporize.

While we can only speculate, based on the fact the transformer is still operational I'll stick with my therory of a thermal condition causing this. I have seen that more than once.