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 Post subject: How to calculate IEPosted: Tue Nov 03, 2009 12:38 pm

Joined: Wed Oct 29, 2008 6:05 am
Posts: 38
What equations/formulas should I use to calculate the IE at various distances for the following application (Large conductor gap):

Voltage: 700VAC
Phase: 3phase delta ungrounded
Conductor gap: 3FT
ISC: 65KA
Clearing time: 2.0 sec or less

Thanks

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 Post subject: Posted: Tue Nov 03, 2009 3:23 pm
 Arc Level

Joined: Wed Jun 04, 2008 9:17 am
Posts: 428
Location: Spartanburg, South Carolina
See IEEE Std 1584

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 Post subject: Posted: Tue Nov 03, 2009 4:06 pm

Joined: Wed Oct 29, 2008 6:05 am
Posts: 38
jghrist wrote:
See IEEE Std 1584

It looks like the IEEE 1584 max gap at this voltage level is 40mm (1.6")???
I need equations for a gap of 36 inches.

Thanks

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 Post subject: Posted: Wed Nov 04, 2009 5:15 am
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1637
Location: Scottsdale, Arizona
About your only choice is to use the 1584 equations except they are only for smaller gaps based on more typical equipment and that could sustain an arc (208 volt arc sustainability is still under review). Using 36 inches as a gap may give you an answer using the equations but it won't be very realistic. It is very unlikely that an arc can be sustained at 36 inch arc at 700 volts. I did some testing a few months ago and could not sustain a 480V arc at around 18 inches.

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Jim Phillips, P.E.
Brainfiller.com

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 Post subject: Posted: Wed Nov 04, 2009 8:45 am
 Arc Level

Joined: Wed Jun 04, 2008 9:17 am
Posts: 428
Location: Spartanburg, South Carolina
PAult wrote:
It looks like the IEEE 1584 max gap at this voltage level is 40mm (1.6")???
I need equations for a gap of 36 inches.

Thanks

The Lee method is used in IEEE 1584 for cases where the voltage is over 15 kV or where the gap is outside the range of the empirical model.

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