Re: Help w/ Chokes

>>From bert.hickman-at-aquila-dot-comTue Jun  4 21:40:39 1996
>Date: Tue, 04 Jun 1996 22:22:00 -0700
>From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Help w/ Chokes
>Tesla List wrote:
><big snip>
>> >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
>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 --


I stand corrected.  Still, two out'a three ain't all bad.  Thank's for that very
informative tutorial explaining BIL. In other words, if we want the 
equivalent of transformer insurance, adopt a pole pig.  I've seen 
large storage yards full of these things, destined for disposal.  All 
they need is a good home.  Hey. I like that.  'Excuse me sir, would you kindly
donate to our local Tesla society's Adopt a Pole Pig Program?

But seriously,  early in my coiling experience I operated a potential 
transformer without an RF choke and it promptly failed (shorted 
secondary mode), whereas the same setup with my pole pig, again no RF 
choke, survived.  This seems to contravene your prediction that 
potential transformers might be better than pigs.  Anyone out there 
have any potentiial transformer stories they'd like to share?

Happy Coiling!, rwstephens