[Hallicrafters] Repotting Transformers.

[Bill Gerhold]

We do this all the time at my work place only on transformers up to 1000
kva.  Your friend is doing it in the wrong order.  First the vacuum, then
the varnish, and then the pressure.  

Its called VPI or Vacuum Pressure Impregnation.  After the vacuum stage, the
varnish is pumped into the tank and the work is allowed to soak and absorb.
Then the air is pumped in under pressure forcing the varnish into the
windings and crevices.  The work piece is then taken to a large oven and
baked for a few days.  It makes the windings, and the core a one piece unit
with no movement of the windings at all and very quiet laminations.  

K2WH
Electrical Engineer in Power Generation,
Transformer Design Engineer and all around
Ham Radio Operator.


-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Roger K8RI
Sent: Friday, July 29, 2005 2:51 PM
To: Hallicrafters at mailman.qth.net
Subject: [Hallicrafters] Repotting Transformers.

I may have mentioned this before, but in case I didn't:
A friend of mine fashioned a metal canister with a fitting on the top that 
would allow him to connect a vacuum cleaner.  He'd fill the container with 
enough "hot" transformer varnish so he could completely imerse the 
transformer without the thing running over.  The transformer, sans covers, 
was then lowered into the varnish, the cover placed on the canister, the 
vacuum cleaner hooked up and turned on.

I don't think he'd run the vacuum cleaner for more than a minute, then while

the varnish was still hot he'd let the air back into the canister. That 
would force the varnish into small internal places that would never be 
reached by dipping alone.  It doesn't take a big vacuum system to do this.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com 

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