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Re: Pole pig rating
Tesla List wrote:
>
> Original Poster: Tesla729-at-cs-dot-com
>
> Hi all,
>
> I was wondering if anyone out there could tell me what the
> term "BIL" means on the nameplates of pole mount distribution
> xfmrs. My best guess is " Breakdown Impulse Level". Is that
> correct?
>
> David
David,
Congratulation! You Score 67% :^)
BIL actually stands for "Basic Impulse Level" in the US and is sometimes
called the "Basic Insulation Level" in Europe. BIL is a standardized
method of testing and specifying equipment so that power systems
designers can properly "coordinate" the insulating capability of the
elements used in power transmssion and distribution systems. Insulation
coordination simply means that the system is designed such that all of
the expensive parts of teh system (transformers, capacitors, breakers,
cutouts) will always have a significantly higher BIL than the lighting
arrestors that protect them.
This means that in a properly designed system, an arrestor should
virtually always break down before a critical element, even accounting
for statistical variation in arrestor breakdown timing and voltage. BIL
is tested using a HV surge generator which is designed to develop an
approximation of a lighting transient - a fast risetime (1.2 uSec)
followed by a relatively slow (50 uSec) decay. Transformers must be able
to withstand the BIL test three times with NO breakdown. A typical 14.4
kV pole pig will usually have a BIL of between 95 and 110 kV. In either
case, this level of insulation makes for one tough beast!
While lots of coilers have done their best to kill many an NST, there's
only ONE coiler (who will remain unnamed, Charles) who has succeeded in
killing a distribution transformer in Tesla Coil service... :^)
Safe coilin' to you, David!
-- Bert --
--
Bert Hickman
Stoneridge Engineering
http://www.teslamania-dot-com