Pole pigs

• To: tesla-at-pupman-dot-com
• Subject: Pole pigs
• From: "Eric Davidson" <edavidson-at-icva.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Tue, 22 Feb 2000 18:37:49 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi all,
 
In an effort to clear the air regarding pole pigs, I'm offering up my
$0.02.   Single HV bushing transformers (pigs with just one 'horn') are
well suited for TC use as long as some guidelines are followed.  A single
primary bushing simply means that one end of the primary is internally
connected to the tank.  This simplifies construction and reduces insulation
requirements.  These transformers are used in both single phase and 3 phase
Y connected banks.  Since a TC is essentially a single ended device, there
is really no need for the HV supply to be isolated from ground (floating),
in fact one end SHOULD be grounded.  The main safety concern is that the
tank (of the transformer) be solidly grounded BEFORE you apply any power to
the unit.  I have never seen a single HV bushing autotransformer, most auto
transformers are used as buck/boost units for voltage regulation or for
close ratio transformations like 2400/4160 delta-wye connections.   In any
event simply look at the nameplate before buying or connecting your
transformer.  DO NOT attempt to drill a hole in the tank and bring out the
other end of the primary on a single bushing unit, this could lead to a
flashover and likely an oil explosion.  My advice is to call T&R electric,
get a 5kVA 13800/240/120 unit with a one or 2 bushing primary and go from
there.  If you get a 2 bushing unit I bet you will be connecting one end to
ground at some point in the circuit.  Hope this helps.  Coil safe.
 
Eric
edavidson-at-icva.gov
 

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