Blown transformer Primary fuse from Secondary overload
Blown transformer Primary fuse from Secondary overload
(OP)
Hi,
At work I noticed a phase loss from one of our transformers. After making some checks I noticed one of the three transformer primary fuses was blown. I am trying to figure out if it was due to a secondary overload, how much current it would take to blow the primary fuse, and why didn't it blow a secondary fuse instead? Here are some particulars that I have:
Transformer
4160/480 vac small pad mounted transformer
Primary fuses- three 65 amp fuses
Secondary fuses - three 175 amp fuses
Normally, the load on the secondary side is pretty light (just some cooling fans for another transformer). At certain times, it is used for backup power for other heavy duty equipment. Between the time there was no phase loss and one was detected, there was an instance where the transformer provided backup for that heavy duty equipment that was giving trouble. Certain members of our team say it was not related. Since it is the only abnormal event we can find I politely disagree. I am trying to prove it could happen. Thanks for any help.





RE: Blown transformer Primary fuse from Secondary overload
It may be a dirty or corroded fuse holder.
It may be a combination of the two.
Examine the fuse holder for signs of overheating.
Bill
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"Why not the best?"
Jimmy Carter
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload
So, you either have a problem in the transformer, inrush or core saturation for some other reason. I have had malfunctioning thyristor rectifiers (missing gating pulses) that caused so much DC in the secondary winding that the core got saturated and drew a lot of primary current.
Do you have any DC equipment on the secondary? If you have that, make sure they don't misbehave.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload
But if there is at least one delta winding, the current relationship between secondary and primary current (at the terminals, what the fuses see) is independent on what winding configuration the transformer has.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload
If you have a 560 A fuse and a 175 A fuse in series, which one blows first when there's an overcurrent?
Right. The 175 A fuse blows. The 560 A will not blow. Ever.
The only possibility that it blows before the 175 A fuse is that there is an internal fault in the transformer (or something else). Right?
Is there an internal fault in the transformer? No, it doesn't look like there is one. You can put in a new fuse and switch on again without any problems? Can't you?
So there you are - something else causes the problem. That "something else" is very often a DC saturation of the core. I have had that several times and it is very often caused by a faulty tyhristor rectifier (disturbed gating pulses, usually), be it a drive, an electrolytic plant or a heavy lifting magnet.
I repeat my question: Is there any DC equipment on the secondary?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload
Then there are a few reasons to see what comes after the 480 V breaker.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blown transformer Primary fuse from Secondary overload
RE: Blown transformer Primary fuse from Secondary overload