Transformer baking Recovery

[Rbethman]

Folks,

Most of us have power, mod, audio, and "other" transformers that have
been "due to storage requirements", exposed to humidity.

The 90 Deg C temp converts to 194 Deg F.

This would seem to be a starting point for a multiple hour bake session.

My Electric stove/oven has a 200 Deg F setting.

I plan to make some baking runs on xfmrs for periods between 2 to 4 hours.

This SHOULD take care of "simple" humidity issues.

Dealing with REAL MOISTURE issues is someplace I've been.  The year was
1975.  My team and I were installing a replacement 1500KW, 4160VAC, 230A
60 Hz synchronous generator.

We were located on the Island of American Samoa.  The military transport
folks, for reason never determined, had left this in an unprotected wood
shipping crate.  This crate sat OUTSIDE for about weeks in the summer
tropical environment AND rains.

We acquired about 12 floodlights, sockets, wiring, and plugs.  We
removed the end bells and confirmed a "Depot Rebuilt" assembly that was
indeed SOAKED.

We baked it with the end bells OFF for two weeks in a water-proof
shelter.  Testing was performed with first a Megger, then followed by a
"Hi-Pot".  We determined that our effort was successful.

Several days later, we installed it, aligned it with the prime mover,
and then, crossing our fingers, started the generator, flashed its
field, and achieved full output voltage.  We did a careful step loading
until we reached full power of 1500KW 4160 3 Phase VAC at a power factor
of 0.8.

It was run for 72 hours in that condition.  It performed flawlessly.

To MY knowledge, this piece of equipment operated for at LEAST four
years without failure.

Baking works!  WE just shouldn't have to go to THOSE extremes to safely
recover OUR transformers.  Unless we have managed to let them get WET.

Bob - N0DGN

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