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Re: 110KV BIL?

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>


BIL stands for "Basic Impulse Level". This is the transient voltage that
your transformers should be capable of withstanding under brief/abnormal
conditions (such as a switching surge or nearby lightning hit). All utility
transmission and distribution equipment has an associated BIL rating. This
allows power system designers to properly "coordinate" the insulation
capability throughout their system. A "safer" path is always provided to
divert abnormally high voltages away from costly equipment via arrestors.
In a properly designed system, an arrestor should always break down before
the voltage can reach the BIL level of more expensive equipment. Designers
can coordinate equipment BIL ratings with arrestors to increase the odds
that the system will continue to operate reliably under normal and abnormal
conditions. A 14.4 kV distribution transformer or PT has a typical BIL of
95-110 kV. 

Note: some Potential Transformers (PT's) may have one HV output that's
rated for a higher voltage than the other HV output - if this is the case
for your PT's, make sure that you make the "common" connection between your
two PT's the Outputs that have the lower voltage rating, and you may also
want to tie this point to ground. For example, I have some 14.4 kV PT's
where one HV output is only rated for 10 kV (max) above ground.   

Best regards,

-- Bert --
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> Original poster: "Ray Haynes by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> On a potential transformer what does the BIL rating mean? My only guess it's
> the breakdown voltage from the high voltage winding to either the case or
> low voltage winding. Is that correct?
> If that is true then if I had 2 potential transformers (120 to 14.4KV) each
> with 110KV BIL then I could connect the HV sides in series (for 28.8KV) and
> not worry about breakdown from either high voltage winding to anywhere (case
> or low voltage winding) caused by the transformers themselves (excluding any
> tesla related arcs)?
> Ray