The Pig Uncovered

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: The Pig Uncovered
From: Tesla List <tesla-at-stic-dot-net>
Date: Wed, 18 Feb 1998 23:41:21 -0600
Approved: tesla-at-stic-dot-net

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From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:  Wednesday, February 18, 1998 12:24 PM
To:  Tesla List
Subject:  Re: The Pig Uncovered

> 
> ----------
> From:  Gregory R. Hunter [SMTP:ghunter-at-mail.enterprise-dot-net]
> Sent:  Sunday, February 15, 1998 2:25 PM
> To:  Tesla List
> Subject:  The Pig Uncovered
> 
> List,
> 
> I took the lid off of my pole transformer, just out of curiosity. In
> the UK, pole pigs are upright rectangular boxes, with the HV
> insulators on the top-front and angled up & out at about 45 degrees.
> My 5KVA, 11KV unit is so heavy, I use a 600 lb dolly to move it
> around, and it's still a struggle.  The thing must weigh 300 lbs.
> That's one thing I was curious about--why does a 5 kilowatt
> transformer weigh so much? I've got some notion as to the the
> required cross sectional area for a 5KVA transformer core, and this
> thing is just too heavy for its rating.  And the SIZE of it--it's
> 20"H x 18"W x 11"D. Nutty.  I've got 2 and 3 KVA autotransformers
> around here no bigger than shoeboxes (powering all my Yank
> appliances).   So I unbolted the lid and took a peek.  As I
> suspected, lotsa empty space in there.  The transformer itself
> occupies less than half of the box. It's under a bath of
> crystal-clear oil.  Why such a big box for such a small transformer?
> I think more than half the weight of the thing is box & oil.

You are probably more than half right. It was originally designed to hang
outdoors in the environment for 40-50 years. So, the case is somewhat over
designed (steel is cheap) and they put in a lot of oil for thermal reasons
(oil is cheap too). BTW, the porcelain insulators aren't particularly light
either (they are, after all, manmade rock).

>  I bet
> the transformer itself is no more than 100 lbs.  The core has a big
> hook eye welded on top.  I'm real tempted to hook a chain hoist on
> that dude and repot it.  If I mounted it in a smaller, lighter 
> container I could probably carry it around by myself.

Probably... Put it in an aluminum tank with less oil, and you'll be all
set. Or even plastic, although putting a HV transformer in an ungrounded
case strikes me as a bit riskier in the event of a flashover. Fortunately,
the BIL rating (probably 90 kV or so) of your transformer is probably much
higher than the output voltage