[Boatanchors] Drying power transformer

[Brian Clarke]

Whoa there, Dobbin.

Polyurethane, wax and pitch all start to fail irreversibly long before 100 C. So 
does the paper used in the inter-winding layer of insulation. Wire often had 
polyurethane coating in the later transformers, too. So, see previous 
sentence. Irreversible damage starts about 45 C, say, 115 F for many 
carbon-based protectives.

Vacuum is a good idea because the boiling point of water and many other 
volatiles drops with atmospheric pressure. So, to accelerate drying, you 
don't need to stress things thermally quite so heavily.

How do you know when the transformer is dry? If you are using a vacuum 
dryer, put a couple of fine-pointed needles in the outlet stream that have 
say 10 to 15 kV between them. When the crackling stops, the exit air is 
dry. Or, use the Hi-Pot test. In Australia, we expect a frame to winding, 
and winding to winding withstand of 4,500 V for telecomms applications.
That may have changed with the new CISPR regulations coming in.

73 de Brian, VK2GCE.

  Ron reminisced:
  Put it in a dryer and if you happen to have a vacuum chamber , use that 
  as well.
  If you can get a heated vacuum dessicator ...all the better.
  Go to 100 C as the transformer should easily handle that.