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Resistance of a pole pig


----------
From:  Chuck Curran [SMTP:ccurran-at-execpc-dot-com]
Sent:  Saturday, April 04, 1998 8:52 AM
To:  Tesla List
Subject:  Re: Resistance of a pole pig

Bart, Erik and All:

I wanted to mention that there is a book available specifically relating to
both pole and pad mounted distribution transformers.  Just in case you need
a nice text to help you fall asleep at night, but also provide some really
nice information on transformers.  The book is:

                                                        TRANSFORMERS,  by
Geber and Edwards
                                                         ISBN:
0-8269-1602-3

                                                        American Technical
Publishers, Inc.
                                                        Homewood, Illinois
60430

The text covers construction, principles, cooling, tap changers, current
transformers, potential transformers and so forth.  Much of it is related to
150 mVa and larger pad mount units, but it is still a very interesting text.
There is a section related to pole mount transformers.  The photographs of
the actual manufacturing plants of General Electric, Allis Chalmers,
McGraw-Edison, Westinghouse and others were of great interest to me.  Many
of the transformers are actually made by Square D Corp. and then nameplated
for their specific customer.

Erik, I was wondering as I read your post if you might be looking for an
idea on if you could overload the pole pig?  If, so, you can easily double
the nameplate rating and others have mentioned going as high as 4 times the
nameplate rating. I've never needed to or tried that level!  Our lab uses
dozens of the 1156D and 1256D series Superior autotransformers that
regularly see 300% overloads for brief moments.  It's always great (for me)
when a new lab engineer doesn't fully appreciate the phrase"brief moments".
That's when the units suffer and are replaced.  I end up with damaged units
that have been repairable and I use them in my current power unit.  It's
easy to know when a locked rotor current test has gone wrong, even in a
240,000 square foot building.  That burning insulation in a motor and/or
autotransformer can cover a very large area quickly!  I mentioned that
simply to emphasize the fact that Tesla service is typically a short duty
cycle situation for most of us.  I was drawing 15 Kw for 4 minutes on 10
minutes off and the transformer never showed any temperature change, using
my "calibrated hand" as the sensing device.

Chuck Curran


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: 'Tesla List' <tesla-at-pupman-dot-com>
Date: Saturday, April 04, 1998 7:54 AM
Subject: Resistance of a pole pig


>
>----------
>From:  Barton B. Anderson [SMTP:mopar-at-mn.uswest-dot-net]
>Sent:  Friday, April 03, 1998 9:24 PM
>To:  Tesla List
>Subject:  Re: Resistance of a pole pig
>
>Eric, calculate it,
>
>Tesla List wrote:
>
>> ----------
>> From:  ESchulz531 [SMTP:ESchulz531-at-aol-dot-com]
>> Sent:  Friday, April 03, 1998 5:49 PM
>> To:  tesla-at-pupman-dot-com
>> Subject:  Resistance of a pole pig
>>
>> Alfred and all,
>>
>>      I am getting a 10kva pole pig, I know that if you short them that
they
>> will draw more then they are rated for, so how would you find there real
>> internal resistance(as in wire and reactance) not the current they are
rated
>> for.
>>
>> thanks,
>>
>> Erik
>
>Find the current by dividing the output voltage (assuming 14.4kv) into the
power
>rating:
>(note: kva and output ratings are rms)
>
>                    P/V=I    or    10kva / 14.4kv = 694mA
>
>Finally, find the impeadance by dividing the current into the output
voltage:
>
>                    Z=V/I    or    14.4kv / 694mA = 20,749ohms at 60Hz (as
pole
>pig is design for).
>
>Hope it helps,
>|_Bart_|
>
>
>