Dry Type Transformer Life Expectancy
Frequently electricians and plant engineers ask how long dry type transformers last. The easy answer is, “Until they fail.” But that answer might result in a ‘click’ at the other end of the phone line. In this case we are talking about general purpose dry type air cooled transformers, 208, 240, and 480 volts. These transformers are located everywhere in manufacturing facilities. For most people they are just metal enclosures that are warm in the winter and make a funny humming sound. We were asked if they were good for 25 years or more.
The biggest enemy of air cooled dry type transformers are roof leaks and fork trucks. The transformers are good for many more than 25 years. But don’t let them get wet, dirty, hit, or buried under “stuff.” They do not like water or heat. If the ventilation is blocked, they may overheat and that will shorten their reliable life expectancy. So, if your general purpose, dry type, air cooled transformer is kept dry, clean, and well ventilated, it may last 30, 40, even 50 years. It should last until you retire, which has become the newest criteria for many electricians and plant engineers. Also, these transformers look innocent, but they are very dangerous, fatal, if they blow up or if something gets stuck inside the enclosure.
We are talking about transformers that might be 1000 kva with a primary voltage of 4160 volts or 13,200 volts and a secondary voltage of 480 or 208. They are in a metal enclosure with vents to allow air to circulate and cool the transformer. These transformers are indoor and usually found in locked electrical rooms. We see these transformers 60 years old and still humming away.
These transformers are definitely deceptive and are very dangerous. Thanks for sharing this information. I have been looking all over for a good explanation.
We recently switched the 2x500kVA 11KV dry transformers off, to replace the main board.
This took place over a period of 3 weeks, is it true that we might have damaged the transformer by letting in moisture due to the off period?
No, unless the dry type transformers are located in a very humid area. The 11 kv primary voltage is fairly low. The transformers should not absorb appreciable moisture, unless the humidity is high or the temperature drops past the dew point at night causing free moisture, dew, to deposit on the windings and cores. We assume you use these transformers indoors, which should be dry and warm. Once the transformers are energized, the heat from the core will dry everything out quickly. Therefore, dry area, dry transformers, no damage, and no loss of life expectancy.
if you have a 750kva dry type transformer 208v primary delta, 277/480v secondary wye grounded….at the secondary side, the transformer will deliver 930.6 amps…however, can you get an additional 150 amp, by overloading it….and if so, can the transformer last 50 years…..
as always, a quick response will be greatly appreciated……Thanks…
No. Heat is a transformer’s big enemy. Transformers are pretty dumb devices, but the manufacturers are very smart. They are not going to overbuild a transformer to reliably take such abuse. Years ago some transformers were overbuilt and just seemed to last and last, even when overloaded. But today there are other concerns besides ‘run to failure.’ There are concerns for the conductor sizing, overcurrent protection, cost of losses, low voltage, reliability, consequences of failure, and most important, SAFETY. Don’t do it. MIDWEST
I have a 13.8 kv / 3000 kva transformer. if i run the transformer at 50% capacity for 10 years then i up the capacity to 90% of the transformer’s output, is the life expectancy less because i ran it in at 50% of it output capacity for 10 years then i up the output capacity to the 90% mark. the reason i ask this question is because we lost a transformer the size i spoke about and we installed a transformer as a temporary and it had been run under the above conditions, does the life expectancy become shorter because when the transformer had been installed years ago at the beginning of its life and the varnish on the coils would have been cooked in at a lower output so when i up the output would that create a problem for how much load it could carry safely.