Huge Arc Flash Boundaries
Huge Arc Flash Boundaries
(OP)
The utility I work for recently had an arc flash analysis done for our plants. It was a given that we had equipment that was "Dangerous" and would have large arc flash boundaries.
What I wasn't expecting was to find that there are a bunch of boundaries in excess of 100 feet, and sometimes much more.
Much of this is high-power generating equipment, many MVA, but I'm still having a very difficult time believing that it has the ability to induce second-degree burns across the distance of half a football field. I strongly suspect this is a case of garbage-in-garbage-out, and some of the numbers for the equations were wrong.
Does anyone have any real world experience calculating flash boundaries where they ran into numbers this high? Is it possible for these hazards to be legitimate? Thanks.
-John
What I wasn't expecting was to find that there are a bunch of boundaries in excess of 100 feet, and sometimes much more.
Much of this is high-power generating equipment, many MVA, but I'm still having a very difficult time believing that it has the ability to induce second-degree burns across the distance of half a football field. I strongly suspect this is a case of garbage-in-garbage-out, and some of the numbers for the equations were wrong.
Does anyone have any real world experience calculating flash boundaries where they ran into numbers this high? Is it possible for these hazards to be legitimate? Thanks.
-John






RE: Huge Arc Flash Boundaries
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Huge Arc Flash Boundaries
I have worked upto 13.8kV Arc Flash System design. What is your switchgear ratings?
RE: Huge Arc Flash Boundaries
RE: Huge Arc Flash Boundaries
David Castor
www.cvoes.com
RE: Huge Arc Flash Boundaries
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If we learn from our mistakes I'm getting a great education!
RE: Huge Arc Flash Boundaries
I'm still amazed, but I'm much more convinced of the authenticity of the results.
-John
RE: Huge Arc Flash Boundaries
As far as clearing times, those are all over the map. We have some utility ties that apparently won't clear for almost 2 seconds, which is pretty phenomenal, but that protection isn't under our control.
-John
RE: Huge Arc Flash Boundaries
rmw
RE: Huge Arc Flash Boundaries
I could point out a location where 110KV overhead lines (four circuits) run directly over houses and yards, but the lines were built in 1908 and the houses in the 1920s ...
Lawyer's Paradise.
rasevskii
RE: Huge Arc Flash Boundaries
Alan
RE: Huge Arc Flash Boundaries
When comparing both methods around 15 kV it seems a bit silly to use these overly conservative results, but to my knowledge it's the only thing available for industrial applications. NESC tables may apply in your situation giving you a HRC and boundary straight away, but I'm not very familiar with those.
RE: Huge Arc Flash Boundaries
I didn't realize that above 15kV results were based on more theoretical calculations. That's interesting to know and probably would explain some of this, however some of these thousand-inch boundaries are for 13.8kV equipment.
Rasevskii,
I did think of the many substations in residential areas, and I believe those are reasonably safe, which is part of why I'm having so much trouble with this. I've seen a lot of high-power equipment go "boom" and I've never seen an electrical incident so intense that it would've caused 2nd degree burns from 50 meters away. You've gotta admit, that's a pretty phenomenal statement, though I do understand these survey results err very much on the side of safety.
-John
RE: Huge Arc Flash Boundaries
RE: Huge Arc Flash Boundaries
1. IEEE 1584 allows you to use a cutoff time of 2 secs with some other considerations. Usually the default time in software programs is around 1000 secs or longer. This will make the IE large.
2. Is there specific areas where the large AF Boundary is? There may be ways of reducing this with changing trip settings on protective gear or installing a arc flash protective relay.
3. On the substation comments, if you look at the NESC for the arc flash hazard it is a single phase fault. These usually have less energy than a 3 phase fault.
For a lot more information on arc flash, go to www.arcflashforum.com