Re: 25 kV PT

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi all,

I tend to think that Scott is right here. Up until recently,
I didn't know that it really mattered which of the two
bushings of the pig (or PT) that you grounded. I thought
that the BiL (basic impusle level) rating meant just what it
said, and for that matter, I still do! Most 14.4 kV pigs are
rated at either 95 kV or 110 kV BiL, and I know that this
is like a 50 micro-second duration impuse, but still, I don't
think that the pig is gonna "fuss" about whether or not H1 or
H2 is grounded, as long as you're keeping the operational
voltages within the design limits. From my personal
experience, I've never even given thought about "which"
bushing should be grounded and I've never had any
problems. Remember, pole transformers must be quite
rugged beast, both electrically and mechanically, to withstand
the occasional voltage spikes caused by nearby lightning
strikes or line switching transients, not to mention extreme sea-
sonal temperature variations and climatic conditions, year after year.
As a matter of fact, I've actually taken the actual internal transformer
assembly out of the tank and the oil and ran it "dry" at up to
280 volts input and it still ran fine. However, I did NOT run
a Tesla coil with the transformer outside of its tank of oil, so
I can't vouch for the transformer's ability to withstand coil
running while "dry". This kind of reminds me of that Castrol
GTX commercial where they ran several different automo-
bile engines with their oil pans drained. Of course the motor
with the Castrol GTX kept running after all of the other motors
with other leading brands of oil had locked up. ;^)) Of course,
thing may be a little different for transformers designed to be ran
indoors, as I'm sure they are probably not quite as rugged as
ones designed to run outdoors.

David Rieben




----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, February 04, 2007 5:02 PM
Subject: Re: 25 kV PT


> Original poster: Scott Kraus <plymouth_4406@xxxxxxxxx>
>
> Hi list,
>
>   Many of you have much more experience with pole transformers than I
> do. I have however taken one apart that had a shorted secondary
> winding. I don't know if all pole pigs are constructed the same but
> the one I took apart had (1) 120 volt winding nearest the core, next
> there were two separate 7200 volt windings and on the outside was
> another 120 volt winding. The core was made up of 2 spiral wraps of
> laminations. I think it was a General Electric unit.
>
> I would think the most insulation stress would be between the high
> and low voltage windings and second at the ends of each layer between
> in the high voltage winding and the core. In the case of the one I
> took apart I'm not sure that it would matter which bushing was grounded.
>
> Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "Dr.Hankenstein"
>
> Neither H1 or H2 may necessarily be closer to ground. Let me explain:
>
> When one winds a transformer, the begining of the winding is refered to as
> "start". When you are done, that's the "finish". While the transformer is
> being tested, such as with a TTR set (transformer turns ratio test set)
the
> polarity marks are commonly refered to as "start and finish" and the test
> set's connections are called "polarity and non-polarity", not H1, H2 to
X1,
> X2, etc.
>
> Now, with the above in mind, a normal "pole" transformer would have the H2
> connected to the "start" of the winding, and the H1 connected to the end
or
> "finish" of the winding. Being that the "finish" or H1 is furthest away
> from the core, you really don't want to ground that end! The "finish" is
> only called "H1" for connection's sake, and it is an industry standard so
> even a Lineman Apprentice can properly hook-up and phase in a transformer
> bank,... just by looking at the pictures. (No offense to the Linemen out
> there, because if it wasn't for the pictures, I probably couln't do it
> either.
>
> If you still confused, use a single-bushing transformer. Then there's
> absolutely no doubt which end is grounded!
>
>
>  > [Original Message]
>  > From: Tesla list
>  > To:
>  > Date: 2/2/2007 11:30:18 PM
>  > Subject: Re: 25 kV PT
>  >
>  > Original poster: "Barton B. Anderson"
>  >
>  > Hi Adam,
>  >
>  > It's probably wise to check with the manufacturer of the pole
>  > transformer to verify H1 and H2. Common sense says H1 is near the
>  > core (but again, check it out first). Here's a document which may be
>  > of some help.
>  > http://www.classictesla.com/download/TransfPol.pdf
>  >
>  > I run my pig with H1 grounded at RF ground. No problems for myself.
>  >
>  > Take care,
>  > Bart
>  >
>  >
>  >
>  > Tesla list wrote:
>  >
>  > >Original poster: Yurtle Turtle
>  > >
>  > >I felt like it should work as well. That's the way I
>  > >run my 4" coil, with one side grounded. However, I
>  > >seem to recall a post where someone stated that their
>  > >14.4 PT got fried by connecting the "wrong" leg to the
>  > >core. I've got lotsa literature on phasing, but
>  > >nothing that would indicate which side of the HV
>  > >windings would be closest to the core (H1 vs. H2).
>  > >
>  > >I also seem to recall a more recent thread, discussing
>  > >which side of a pig to ground. I can't find it now. I
>  > >think Dr. Resonance may have had an opinion or facts
>  > >on this.
>  > >
>  > >Adam
>  > >