2500KVA Bayonet fuse blown; result unbalanced load to plant

[Rodney.Ferguson]

Problem detail:
We faulted on our main 480V 3800A switch gear for unbalanced load. C phase dropped from 484V to 250V. Our team dropped out all feeders from our main. We then went to 325V on C phase. Root cause C phase bayonet fuse of 120A on our 13KV line side of transfomer blew. Our load fuses were intact. Our main switch showed no fault other than unbalanced load.

Actions:
We immediatly turned all feeders off. (Lost a few fuses). Megged out all high HP motors. All good.
Secondary fuses on 2500KVA transformer; okay. Main feeder (13KV) to transformer; okay. The only fault was the Bayonet fuse on primary side of 2500KVA tranformer.

Question:
How? Power provider states it came from our side. We checked major power consumers and found no problems. After we powered everything back up without any repairs we have ran for 1 week with no futher problems.
Has anyone seen similar porblems? Could the power provider be at fault? If so, what data could be requested to find out?

Any help would be appreciated.

 

[LEO2854]

Welcome to the forum.
it sounds like some type of surge ,maybe a lighting strike in the area?
what is the condition of your 13/8KV 480V Transformer?

 

[mivey]

I seem to recall some heating issues with the fuses for the larger transformers (like the 2000 & 2500) when they were heavily loaded (and maybe even in a hot environment). I think they made a retrofit to have silver contacts or something but we just went with cutouts for the larger pads. I'd have to look for the note as it has been a few years.

 

[jim dungar]

Power provider states it came from our side. We checked major power consumers and found no problems.

Welcome to the world of finger-pointing.

Yes, it is possible that due to a lack of coordination some event in your facility caused their protective device to operate. It is also possible that the cause was in their system.

I assume you do not have any of your own power monitoring/recording equipment, and that it was set up to at least record Min-Max voltages and currents. If not you will have to trust the utility to tell you what actually happened.

But, if you did not need to replace/reset any of your protective devices, it is unlikely you caused the outage.

 

[zog]

Have you tested the transformer? What were the results?

 

[jghrist]

If there was an internal fault in the transformer that caused a primary fuse to blow, it is very unlikely that the transformer could be successfully re-energized. Sounds like miscoordination between the primary and secondary fuses or maybe a faulty primary fuse. First thing to do is check the coordination.

 

[mxslick]

If there was an internal fault in the transformer that caused a primary fuse to blow, it is very unlikely that the transformer could be successfully re-energized. Sounds like miscoordination between the primary and secondary fuses or maybe a faulty primary fuse. First thing to do is check the coordination.

I respectfully disagree with the part I put in bold. I have been witness to a few cases with padmounts where the fuse blew on an internal arcing fault, was replaced and held for an extended period of time after. In one case another internal fault finally took it out for good, and one of the others was a violent failure on the second go. Same thing with pole-tops.

I do agree that a bad primary fuse from the start could be a culprit here. It was probably on edge from the beginning and finally let go.

I don't feel miscoordination was the case here, but a remote possibility.

Bad primary fuse or a fault on the utility side is my vote. But good luck getting the utility to admit to anything.

Perhaps the OP can contact other facilities in the area on the same feeder and see if they experienced any problems.

 

[Rodney.Ferguson]

None of our distribution buckets nor our main was tripped. The secondary side of the transfomer's fuses were intact. Only 1 bayonet fuse on the primary blew.

 

[zog]

None of our distribution buckets nor our main was tripped. The secondary side of the transfomer's fuses were intact. Only 1 bayonet fuse on the primary blew.

Right, which makes the transformer itself the leading canidate here, what were test results?

 

[jim dungar]

Who owns the transformer, you or the utility?

 

[Rodney.Ferguson]

Power company owns the transformer.

We have 2 different substations that can supply power. 13KV lines come into a switch (The switch is fused from both substations). Then feeds the transformer. The switch fuses were intact.
The secondary side of the transformer's fuses were intact.

 

[zog]

Power company owns the transformer.

We have 2 different substations that can supply power. 13KV lines come into a switch (The switch is fused from both substations). Then feeds the transformer. The switch fuses were intact.
The secondary side of the transformer's fuses were intact.

I am confused, so you don't take ownership of the system until the 480V? I am reading some conflicting information in your posts, maybe I am nto reading it right, have a one line?

 

[jim dungar]

Power company owns the transformer.

Typical, utility owned fuses open on the primary side of a utility owned transformer and the utility blames the customer.

Very rarely does a utility ever care about coordinating their protective devices with a customer that purchases at 480v.

 

[dbuckley]

Welcome to the world of finger-pointing.

Ain't that the truth

 

[boboelectric]

Was the fuse link "blown" or melted from a poor contact?

 

[mxslick]

I am confused, so you don't take ownership of the system until the 480V? I am reading some conflicting information in your posts, maybe I am nto reading it right, have a one line?

I have heard of situations where the POCO owns/maintains the transformer, the customer owns and the POCO maintains the transformer, and customer owns AND maintains the transformer.

Sounds like the OP's situation is POCO owned/maintained. In that case the POCO should be able to tel you the condition of the transformer and if the did a DGA or other tests.

To the OP: Did you check in with others in your area to see if they experienced any problems? That may help determine where the problem originated.

 

[gfstanley]

I wonder if the primary fuse arrangement is close coupled to the primary bushings of the xfmr, and if the connection is by unshielded jumpers or a hard bus connection? Unshielded jumpers are notorious for causing problems on the primary side of a xfmr in an industrial facility. Usually these would be destroyed during the fault, but not always.

Also, I would check to see if there is any metering between the primary fuse arrangement and the primary bushings of the xfmr. There migh be a Potential Transformer (PT) connection for metering that could have faulted, blown clear, and you may not miss being out of service.

Another possibility is a rodent, but usually there is some physical evidence.

It would be interesting to shoot the primary fuses, or switch if there is one, with an ultrasonic gun to see if there is any corona or partial discharge activity in and around the primary side of the service. If it is accessible, I would shoot the primary fuse arrangement with an infrared camera. Good luck.