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Re: Help w/ Chokes

Tesla List wrote:
> 
> >From rwstephens-at-ptbo.igs-dot-netMon Jun  3 22:22:57 1996
> Date: Mon, 3 Jun 1996 18:11:57 -0500
> From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: Help w/ Chokes
> 
> >Date:          Sun, 2 Jun 1996 22:25:20 -0600
> >From:          Tesla List <tesla-at-poodle.pupman-dot-com>
> >To:            Tesla-list-subscribers-at-poodle.pupman-dot-com
> >Subject:       Re: Help w/ Chokes
> >Reply-to:      tesla-at-pupman-dot-com
> >
> >>From jim.fosse-at-bdt-dot-comSun Jun  2 21:51:14 1996
> >Date: Sun, 02 Jun 1996 18:03:39 GMT
> >From: Jim Fosse <jim.fosse-at-bdt-dot-com>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Help w/ Chokes
> >
> >On Sun, 2 Jun 1996 00:25:25 -0600, Tesla List
> ><tesla-at-poodle.pupman-dot-com>, you wrote:
> >
> >
> >>From: Wallace Edward Brand <webrand-at-dgs.dgsys-dot-com>
> >> EEI-NEMA
> >>Standards for Distribution Transformers, Overhead Type-- Sixth Report EEI
> >>Pub. No. 55-14, NEMA Pub. No. TR2-1956, May 11, 1956.  The exact title of
> >>the book is "Electric Utility Engineering Reference Book, Volume 3,
> >>distribution systems.  Effective February 1, 1989, Westinghouse transferred
> >>its intellectual property rights in the book to Asea Brown Boveri.
> >>They operate as ABB Power Systems Inc., Advanced Systems Technology, 777
> >>Penn Center Boulevard, Pittsburgh. Pennsylvania 15235-5927  I hope this is
> >>helpful.   The quoted statement appears at page 206.  Wallace Edward Brand
> >>
> >Wallace,
> >       Thank you, I was looking for the transient over voltage limit.
> >I'll check with the library about getting a copy of the book.
> >
> >       jim
> 
> Hi Jim and others,
> 
> My 16 kV, 10 kVA pole pig has a test specification called B.I.L.
> which I believe stands for Basic Impulse Level.  The nameplate says
> BIL 120,000 volts.  This I believe is the rating to look for in a
> good Tesla-able power transformer, the higher the BIL the better.  It
> must be linked to lightning induced transient survival.  Hope this is
> of some use.
> 
> Happy Coiling! rwstephens

Robert,

Since I'm actively looking at buying a pole pig, I just completed a 
little research into the insulation capabilities of distribution 
transformers. In chapter 4 of "Electrical Distribution Engineering", 
Anthony J. Pansini, McGraw Hill Book Company, Copyright 1983, ISBN 
0-07-048454-6, the author defines BIL as "Basic Insulation Level". This 
is a design standard which is apparently specified by the National 
Electric Safety Code to permit power distribution equipment to be 
"coordinated" with protective equipment (such as lightning/surge 
arresters or the transformer bushings themselves) in such a manner that 
the LAST thing to break down will be the transformer's windings. 

In the presence of a switching or lightning-induced voltage surge, a 
nearby arrester should fire first. If that fails, then the transformer 
bushings or an internal spark gap should fire next, thereby preventing 
the transformer windings from "seeing" a surge of sufficient magnitude to 
cause internal breakdown and damage. A standard surge test waveform is 
used to verify the BIL of equipment. The waveform has a 1.5 uSec risetime 
to the peak and a 40 uSec tail going back to half the peak voltage. This 
waveform is used to simulate lightning surges which are normally more 
prevalent and potentially damaging than switching surges.

A portion of a table is repeated below for the range of transformers 
coilers are typically interested in. Note that these are minimum BIL's - 
your transformer is significantly higher than the minimum:


Voltage    BIL (KV)              BIL (KV) 
 Class   (Distribution         (Power Class -
 (KV)        Class)         Station/Xmission Line)
 -----   -------------      ---------------------
  8.7          75                   95
  15           95                  110
  23          110                  150


As can be seen, pole pigs are built to withstand punishing voltage 
surges, a fraction of which would cause even 15 KV neons to whimper and 
go "belly up". There does not really seem to be a lot of difference 
between 15 and a 23 KV voltage class pigs in terms of BIL - they both are 
GREAT! Since potential transformers are typically used in substation 
applications for a variety of voltage and power measurements, it also 
would appear that, on the average, potential transformers may offer even 
greater surge resistance than pole pigs. 

In any event, it is now clear why coilers go through large numbers of 
neons but (to my knowledge) have never killed a pole pig!


Good/Safe Coiling to ya..


-- Bert --