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 pstr-m01.ygpweb.aol.com]
Close up of lose brace:
[Linked Image from pstr-m02.ygpweb.aol.com]