Dry-type Transformer Outside

[WoodrowJWeen]

I want to put a 225 kVA dry-type transformer outside, which seems pretty ordinary. However, this transformer will only be energized when an outdoor emergency generator is running. I am concerned about moisture getting in the insulation during the long periods of non-use. Has anyone encountered such problems with a similar installation? If so what was done? Add heaters maybe?

 

[davidbeach]

I would suggest heaters on a thermostat. I once did something similar to protect transformers in a parking lot in Fairbanks, Alaska, where the transformers supplied block heater receptacles and were not energized until the temperature was below freezing.

 

[PWR]

Since in that size transformer the normal practice would be liquid insulated, why deviate from that? Are both primary and secondary low voltage?

 

[dpc]

My own personal preference would be to NOT put a dry-type transformer outside if it was not going to continuously energized. I'd find some way to put it indoors or buy a pad-mount oil-filled unit.

We generally never put conventional dry-type transformers outdoors. A cast-coil transformer is a different story, but the oil-filled will be cheaper.

If you must, then certainly space heaters are an absolute necessity. I'd leave them on all the time.

 

[davidbeach]

Depending on summer temperatures it may be worthwhile to have the heaters on thermostatic control. If the generator only runs for relatively short periods of time, there's probably no need to cut out the heaters when the transformer is energized. In my example above, where the transformers could be energized for weeks or months at a time, the heaters were turned off when the transformers were energized.

I'm not aware of oil-filled or cast-coil transformers for 480-208V applications. That isn't stated in the O.P., but given the small size, it seems likely.

 

[itsmoked]

Too bad the xfmr can't be energized all the time..

 

[WoodrowJWeen]

So is the insulation on dry-type transformers that different from the insulation on the generator(which sits outside too)? This is all low voltage (<600v) equipment.

 

[alehman]

Consider a totally enclosed non-vented dry-type transformer with heaters.

 

[BJC]

Don't forget about bugs, spiders and rodent's. A NEMA 3R tansfromer isn't exactly closed. They are good for falling water and you can get rodent screens but things you don't want will find a way in there.
IF you can't use an oil filled xfmer then keep it energized all year or build a house for it.