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#5919 12/13/01 09:46 PM
Joined: Aug 2001
Posts: 599
Nick Offline OP
I went on a service call last night to a hospital we did a few years back. One of the substation transformers was making an awful noise, like there was a lose bolt running around. This is a 12.47KV to 480/277V 2500KVA dry type transformer. What I found was the brace in the pictures lose and vibrating. As you can see by the close up there is some material that has flaked off giving evidence this has been going on for some time. The lock washer in the lose connection was fully compressed and the bolt was tight. It took a lot of effort to tighten this bolt enough to secure the brace. I got maybe a turn with a big wrench. The rattling is now gone.
Transformers are noisy as we all now especially ones of this size but this particular one is louder than the 5 others of the same size on the project.
My questions are as follows:
1) Given that the bolt was tight but the brace still rattled do you think we, as a contractor should assume any liability for it coming lose, or write it up as lack of maintenance? I feel it was reasonably tight at the time of installation and the tolerance between the brace and its support bracket was not to spec. When I tightened it, it felt like I was actually squeezing the angle bracket.
2) Why do you think in normal operation this transformer is louder than others just like it? When we got there and it was energized we had to yell to hear each other. Like standing next to a large generator. After de-energizing we could talk in normal tones even with the emergency substation transformer (a 1500KVA unit just like it and right behind us) running the emergency loads.
Overall view:
[Linked Image from]
Close up of lose brace:
[Linked Image from]

#5920 12/14/01 12:55 AM
Joined: Jun 2001
Posts: 642
Charge for the service call. Over a year since install.

#5921 12/14/01 07:41 AM
Joined: Mar 2001
Posts: 2,056
It seems that more loose hardware or vibrating panels is the most likely cause of that much noise. Did you grab onto, or push on various structural components to try to dampen vibration?

#5922 12/14/01 06:42 PM
Joined: Oct 2000
Posts: 5,392
Why something staionary , no moving parts, makes noise is interesting. [Linked Image]

#5923 12/14/01 08:20 PM
Joined: Oct 2001
Posts: 41
I may be all wet here but is that supposed to be a shipping bracket? And supposed to be removed after installation. I’ve never installed anything larger than 660KVA but I seem to remember having to remove some shipping hardware.

#5924 12/14/01 11:58 PM
Joined: Aug 2001
Posts: 599
Nick Offline OP
Well, it has been decided to charge for the call. Sometimes we do free bees for clients, even after the warranty period, when there is a prospect of more work in the future.

The transformer vibration, normal in a transformer of this type, is causing some of the dead fronts to rattle on the switchgear. Not much could be done about that. My concern is why is the normal transformer hum from this one louder than the others.

Yes, the braces are supposed to be there. It might be hard to tell in the picture but those coils are about 5ft tall. I don’t know how much they weigh but I am sure it’s a lot. The core frame sits on vibration dampeners and the mounting bolts are loosened slightly per manufacturer instructions. In a seismic event, without the braces, you could have a catastrophe! This facility is designed to survive an 8.5 magnitude earthquake and still be in full operation. That was the slogan during construction. “Built to Survive an 8.5”

#5925 12/15/01 09:28 AM
Joined: May 2001
Posts: 378
could the xformer be faulty we had one that loud and it turned out that the noise was excessive core clapping,bad laminations we called the manufacturer I will ask a xformer builder builder I know and post back if you like?

#5926 12/16/01 02:06 AM
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and

I was thinking in the lines of what Frank said - maybe the core is causing the excesive noise.
From the looks of the pics' you have posted, the enclosure looks like a fairly rigid and dampened assembly.
That, coupled with the Seismic Restraints Designs, would make it's enclosure and mounting assemblys secure enough to only pass on sound levels in the 10 to 20 dB range [max], and frequencies from 360 Hz to whatever Harmonics are available [360 being the most pronounced and the fundamental].

If you can inspect the core sometime, maybe part of the Epoxy Potting will have visible failure [cracks, chips, etc.]. I would look on the core and each coil.
Try pressing the laminations together to see if anything "snaps" or moves. [that's just a "let's see if" deal!].

Lastly, maybe one of the coils has a voltage tap jumper in the wrong position, or maybe one coil was connected wrong at the factory.

This really is starting to sound like a core [magnetic core and coils] problem now to me.

I have been able to quiet down noisy transformers after installation by just patiently tightening the enclosures and securing the diamond cladding mesh on the bottoms [if used]. Of course, this has been on Xformers of less than 750 KVA, with the highest Primary voltage of 480 VAC and mostly indoors.

Let us know what the outcome is.

P.S. If the culprite is the core, it's just a matter of time before the bolt you tightened begins vibrating roughly again and the whole thing begins again.
I bet there's very fine powdery dust around that bracket, which looks kind of Iron / Steel - ish.
Another thing to bet on is that if you were to remove the bolt and look at the mounts, the hole[s] will be much larger than they should be and possibly oval, instead of nice and round.

Just a hunch!

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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