Re: PT Questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Steve,

At 11:04 PM 4/27/2002 -0600, you wrote:
>Hi,
>
>I have questions about HV Potential/Instrument Transformers of the type some
>use to power their TCs:
>
>1) Why are they so "beefy" so that they are at least 1 KVA?  Are they used
>to power a few lights or other things as well as a voltmeter that only
>requires miniscule power?

They must stand rain, hail, heat, cold, lightning, wind...  all in the
extreme...  They often are used to detect "unusual" line voltages so they
are designed to "take a hit" electrically too.

>
>2) Are most PT primaries "two-horn" style with neither primary side
>grounded?

I think so.  Being instrument transformers they do not have grounds to
prevent ground loop errors.

>
>3) Are typical PTs dry, oil immersed, or potted?

Most or potted in a big molded plastic case.  I think there are some pig
like oil immersed versions too.

>
>3) Does anyone in the US have one for sale at a reasonable price?  I am
>interested in a two-horn ungrounded configuration, 14 KV at around 2-3 KVA
>intermittent duty,  120 or 240 volt 60 Hz secondary, preferably dry style.
>I prefer an ungrounded HV winding so it can drive a bridge rectifier with
>one side grounded.
>
>4) What commercial source has the best deals for them?  T&R?  Austin?
>
>5) Do utility companies take them out of service?  Seems like they would
>last forever and not need replacement.

Things change, especially now that so much old overhead wiring is being
moved underground.  Any "designed" change to wiring specifies new equipment
since "recycling" old equipment is not the power company's "way".  You
don't want to throw the switch on a 2 million dollar job just to have a
reused 30 year old PT flame out... 

Cheers,

	Terry



>
>Thanks,
>--Steve
>
>