It is currently Sun Oct 22, 2017 3:12 am

Author Message

 Post subject: IEEE 1584 Equation GlitchPosted: Fri Mar 04, 2011 5:55 am
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1207
Location: Scottsdale, Arizona
There is an interesting glitch with the IEEE 1584 equation for arcing short circuit current at or above 1 kV.

The equation for arcing current at higher voltages > 1 kV:

Log Ia = 0.00402 + [0.983 (Log Ibf)]
Ia = 10^(Log Ia)

Where:
Ibf = 3 phase bolted short circuit current in kA
Ia = 3 phase arcing short circuit current
IEEE range of validity 700A to 106 kA

Hereâ€™s the glitch. If the bolted current is 1,000 Amps i.e. 1 kA:

Log Ia = 0.00402 + 0.983 X Log (1)

Log of 1 = 0
Therefore:

Log Ia = 0.00402 + 0.983 X 0
Log Ia = 0.00402 + 0
Log Ia = 0.00402

Ia = 10^(Log Ia)
Ia = 10^0.00402 = 1.0093 kA

Soâ€¦.. Ibolted = 1,000 Amps and Iarcing =1,009.3 Amps

Except it is physically impossible to have Iarcing greater than Ibolted.

Oops!

_________________
Jim Phillips, P.E.
Brainfiller.com

Top

 Post subject: Posted: Fri Mar 04, 2011 6:29 am
 Sparks Level

Joined: Tue Feb 24, 2009 7:05 am
Posts: 252
brainfiller wrote:
Except it is physically impossible to have Iarcing greater than Ibolted.

Oops!

Not very surprising since the IEEE 1584 equations were curve-fitted from the actual data. Some points will be over or under what's physically possible.

It somehow reminds me of 2 AA batteries of mine which, after use, had a negative voltage between the ends (-0.2 V and -0.3 V). I think they gave me too much energy, and now try to get some of it back. Not going to happen...

Top

 Post subject: Posted: Fri Mar 04, 2011 6:54 am
 Arc Level

Joined: Wed Jun 04, 2008 9:17 am
Posts: 409
Location: Spartanburg, South Carolina
The glitch is only relevant for bolted faults < 1.734 kA. This probably won't affect many high incident energy locations.

Top

 Post subject: Posted: Fri Mar 04, 2011 8:33 am
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1207
Location: Scottsdale, Arizona
jghrist wrote:
The glitch is only relevant for bolted faults < 1.734 kA. This probably won't affect many high incident energy locations.

I am sure you are quite correct. I can't imagine that low of a current even sustaining easily.

Just thought the little(?) hiccup was interesting.

_________________
Jim Phillips, P.E.
Brainfiller.com

Top

 Post subject: Posted: Thu Mar 17, 2011 1:35 pm
 Sparks Level

Joined: Mon Jul 09, 2007 11:43 pm
Posts: 51
Location: Sheffield, England
Hi Jim, I came up with a similar scenario for voltages under and approaching 1000 volts about three years ago. I said at the time "how can you get an arcing current which is greater than the bolted current. You can easily get arcing current which is 50% higher than the bolted short circuit current value. WDeanT kindly posted the following link which is very interesting. The perils of curve fitting equations!!!

Top

 Post subject: Posted: Fri Mar 18, 2011 3:04 am
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1207
Location: Scottsdale, Arizona
Mike Frain wrote:
Hi Jim, I came up with a similar scenario for voltages under and approaching 1000 volts about three years ago. I said at the time "how can you get an arcing current which is greater than the bolted current. You can easily get arcing current which is 50% higher than the bolted short circuit current value. WDeanT kindly posted the following link which is very interesting. The perils of curve fitting equations!!!

Hi Mike,

Forgot about that post. Good info!

Thanks!

_________________
Jim Phillips, P.E.
Brainfiller.com

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 6 posts ]

 All times are UTC - 7 hours

#### Who is online

Users browsing this forum: No registered users and 1 guest

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

 Jump to:  Select a forum ------------------ Forum Library / Articles The Lounge    Question of the Week - What Do You Think?    Arcflashforum.com Feedback and Announcements    Off Topic Discussions    News in Electrical Safety    Captions Arc Flash and Electrical Safety    General Discussion    Electrical Safety Practices    Equipment to Reduce Arc Flash Dangers    Personal Protective Equipment (PPE) Arc Flash Studies    General Discussion    Arc Flash Labels    Software for Arc Flash Studies    System Modeling and Calculations Codes and Standards    CSA Z462 Workplace Electrical Safety    EAWR Electricity at Work Regulations, HSE - Europe    OSHA CFR Title 29    IEEE 1584 - Arc-Flash Hazard Calculations    NFPA 70 - National Electrical Code - NEC (R)    NESC - ANSI C2 - National Electrical Safety Code    NFPA 70E - Electrical Safety in the Workplace    2015 NFPA 70E Share It Here    Arc Flash Photos    Your Stories
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883