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ubject: RE: Arecibo transformer
Date: Thu, 16 Jun 2011 14:39:27 -0400
In-Reply-To: <20110615155338.GA10705@ceiba.naic.edu>
Thread-Topic: Arecibo transformer
From: Robert McNaughton
To: Mike Nolan

Dear Dr. Nolan,

I'll be sending you multiple e-mails with photos of your transformer
attached. We're working on the estimate but there are a number of
things we have to discuss first. I'll try to outline them here but we
may need a conference call to discuss them more thoroughly.

Transformers like yours are designed with bolt-on covers because the
customer goes inside frequently and makes changes.

It is my understanding that your team has never gone inside the
transformer to make changes since you took possession. I know
Continental went inside multiple times because they were having problems
with the rectifier assembly due to faulty solder joints when it was
being built.

Now that you have some transformer experience, do you think your team
will be going inside the transformer for any reason to make repairs? We
already know there isn't anything you can do on the transformer side but
you still feel confident you could make field repairs to the rectifier
side if there was a problem.

We have to discuss these topics because the root cause of failure was
moisture in the oil. This is something that was occurring over an
extended period of time. The transformer oil was saturated with water
and the entry points were the cover gaskets. The moisture in oil
test(D-1533), dated 4/13/11, suggested the oil was saturated with water
at 69 ppm and the attached photos confirmed this.

The core and coil assembly(C and C) was sitting in at least one(1) inch
of free standing water at the bottom of the transformer tank.

My recommendation would be to go with a one(1) piece solid weld-on cover
to keep humidity and rain water from entering the transformer. If you
select this option, you won't have access to the rectifier assembly.
There are trade-offs. This is the best way to keep water out but it
also keeps you from making field repairs to the rectifier.

Since you are located in the tropics and this transformer is vital to
your operation, I would recommend a positive nitrogen system(PNS), with
alarms, on your transformer. The positive nitrogen system will keep the
transformer dry and if a problem develops, the alarm will notify you
immediately so you can take action. If you are interested in these
options, a quote can be provided.

I'm also trying to engineer a weld on cover for the transformer side and
a bolt-on cover for the rectifier side but I'm not sure it can be done.
You'll still need the positive nitrogen system and you'll need a domed
false cover, with drip edge, over the whole transformer to shed rain
water away from the gaskets.

Best Regards,

Robert