Life of transformer

[rookie4now]

I was on a job last week and the owner asked me a question that I couldn't answer. There is a transformer in a vault on the property. I don't have much in the way of specs on the transformer. It is approximately 7' x 5' x 4'. The building has 800a 120/208. I assume it's a step-down transformer, but I don't know for sure. The question was, "how long do they usually last?" I'm really not sure. My guess is that 30-40 years is not unusual, but I really don't know. I believe it was installed in the late 60's early 70's so it probably has PCBs.

Anybody know what typical life on these guys is? Also, for my own curiosity, what does a transformer like that cost?

 

[mxslick]

It is most likely a step-down transformer, and is probably owned by your POCO (Utility Company) they should have all the info on it, including when it was installed and when it had it's last oil sample taken and the results.

IF and ONLY IF the transformer has NO exposed connections, you could carefully approach it and see if it has a data plate on it with all the information you need to know. BUT DO NOT TOUCH IT, just to be safe.

Generally speaking, a transformer of that type should last in excess of 40 years or more, (which from your guess it is about that old now) but it depends on many factors, such as how many overloads/overvoltages it has seen, the magnitude of the same, the quality of it's original construction and the insulating liquid in it, how much contamination (if any) is present in the insulating fluid, etc.

But bear in mind that one severe fault can easily damage even a good transformer beyond repair.

There are companies that specialize in testing transformer oil and the transformer itself to help predict how much useful life it has left. (I think zog's company offers that service?)

Modern transformers don't seem as durable as the older ones, I have seen some fail in a few months but the newer generation seems to only average about 15-20 years of useful life.

Some other folks here (like iwire, who does a lot of commercial work) could give more insight.

As for cost,, it's a lot....in excess of $10,000 or more. Testing is expensive but a lot cheaper that a replacement and the associated downtime. :grin:

 

[zog]

Sorry, can't tell you much about this transformer without any information. Oil? Gas? Dry?

10-100 years is the best answer I can give you. Oil filled tend to last longer if they are properly maintained, the most important indicator is obtained from a DGA sample to check the 9 different gasses present. They can tell you everything about the past and future life expantcany of the transformer. Sure we do it but lots of testing companies do, DGA should only cost $500 or so from a local company.

The main factor for life expantancy is tempature, even if the max is only exceed for a few minutes the result can be major.
Class ?A? insulation - 8C above max temp rating= ? life expectancy
Class ?B? insulation - 12C above max temp rating= ? life expectancy

Again, a DGA will be able to tell if overheating has ever occured.