Bil

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mike0w

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Basic impluse level, "is the insulation strength expressed in terms of the crest value of the withstand voltage of a standard lightning impulse voltage wave."
is this correct? where could i find more information on this topic, is it in any IEEE books? (color books) Just curious reading some switchgear specs. for outdoor metal clad gear 13.2kv and it is refering to the BIL and I was just wondering where I can get some more information on this to gain a better understanding of the subject. Thanks in advance.
 
Find a copy of the Electrical Transmission and Distribution Reference Book. It was published by Westinghouse many years ago, but it is a staple of "old timers" personal libraries.

I believe ABB has re-published it in recent years, but don't hold me to that since I have never actually seen a copy of it. I have the "old timers" version.

Also check in the Standard Handbook for Electrical Engineers, under lightning and overvoltage protection.
 
I have a copy of the ABB "Transformer Tests", "Their Purpose and Importance" publication B-713 which was originally published by Westinghouse. Impulse tests are made with wave shapes that simulate those a transformer may be exposed to while in service. Note the words "wave shapes" which means more than one.
There are (3) basic waves which are commonly used wich include, chopped wave(CWW), full wave, and front of wave (FOW).
One document that I have further describes the FOW as indicated by ANSI C62.2 as being in the range between 1.3 and 1.5 times the BIL ratin with the "time to chop" occuring at 0.5 micro sec. For coordination purposes the FOW strength of 1.4 times the BIL should be used.
CWW withstand voltage levels for different transformer HV BIL ratings are listed in ANSI/IEEE C57.12.00, the levels of which correspond to 1.1 x BIL, and the "time-to-chop" occurs in 3.0 micro sec.
The "Full Wave" withstand voltag(BIL) is equivalent to the HV BIL rating of the transformer which voltage occurs as a straight line from 8-50 microsec.
There is also a 4th caled "Switching impulse level" (BSL), the ratings of which are included in ANSI/IEEE C57.12.00 the levels of which correspond to 0.83 x BIL extending from 50-2,000 microsec.
 
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