How to modify Table 410-1 calcs when using hot sticks and IEEE 1584

It is my understanding based on reading Appendix F of the 2005 Fed OSHA 1910.269 proposed rule making, http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=FEDERAL_REGISTER&p_id=18361 and reading threads on this forum, that table 410-1 of the NESC was designed with rubber gloving in mind.

I work at a utility that uses hot sticks. My arc flash calculation software is SynerGEE by GL (formerly Advantica). This is the same program that we use for load flow and protection coordination studies. The SynerGEE software uses the IEEE 1584 method of calculation or the Lee Method for >15 kV or bus gaps greater than 6 inches (153mm). SynerGEE calculates results for single phase, acknowledging that the results are conservative because the IEEE formulas are based on three phase testing. I understand that the IEEE method is based on three phase faults and can handle open air or enclosed scenarios. On the other hand, the NESC tables are based on open air, phase-to-ground fault calculations using ARCPRO. I have no experience with ARCPRO and would ideally prefer to avoid another program.

I would like to use SynerGEE, therefore IEEE 1584 calculations (or Lee Method) to conduct an arc flash analysis of an overhead and underground 12.47 kV phase-to-phase distribution system for a utility (NESC applicable, not NFPA 70E) that uses hot sticks.

I would appreciate any general advice on the major areas of consideration for me as I conduct the arc hazard analysis.

I also have questions on specific details to consider.

1. For hot stick work on 12.47 kV phase-to-phase systems, rather than using 15 inches for a working distance per Table 410-1, are utilities using the minimum approach distance (MAD) minus twice the arc length, as was done in Table 410-2? Or, are you just assuming some reasonable working distance related to the length of the stick being used, perhaps 4' for a 6' stick, or 6' for a 6' stick?

2. If using the MAD calculation to define a working distance, are you basing the arc length on the 10kV/inch calcuation (12.47 kV/1.73/10=0.72 inches) and then using this distance as your arc gap for the IEEE calculations? It is my understanding that the arc length in the MAD calculation is assumed to be the shortest possible length, which would be equal to the arc gap.

3. If the working distance is simply defined by reasonable judgement, are you sticking with an arc gap within the valid range of IEEE Table 4 (0.5"-6") or are you selecting an arc gap value greater than 6", which would require the Lee method of calculation?

I know you say you want to avoid another software package, but for the high voltage calcs, I would strongly recommend that you purchase Arcpro. There is virtually no learning curve with it and it is inexpensive as software packages go.

I figured you might say that about using Arcpro. I was ready for that answer.

With your utility experience, I was hoping you might weigh in on the more detailed questions that I've asked.

For studies we have done for utilities, we have used both the 15" working distance from NESC Table 410-1 for glove work and a larger distance (5') for use where hotsticks are used. We show both values where the 15" working distance results in IE > 4 cal/cm². We use Arcpro with the arc gaps used in NESC Table 410-1.

Arcpro will give much less conservative values than IEEE 1584. Generally, for line work where you can block reclosing and use instantaneous or a fast trip curve, we have found IE < 4 cal/cm² with the 15" working distance. Large IE only occurs in substations where there is no fast bus tripping.

Well figured I would tackle the easiest first. I have yet to see 15 or 25 kV feeders have as much as 8 cal, but I expect there are some out there that do (with slow time curves and no inst). Usually worst case that we have seen is 6 to 8 and that is with many seconds of operating on the time curve. So if you don't expect the worker to hang around for 10 seconds, use a cut off time for IE. When you go to an 8' stick, it really does not matter if you use 6' or 8' because the IE drops off quickly as the inverse of the square of the distance increase. So if you have 8 cal at 15" you will get 2 cal at 30".

We use the gaps from the NESC for utility work.

And always recommend non-reclose for hot work.

The other reason I suggested Arcpro up front is that it will greatly simplify the issues you are dealing with.

As jghrist said, the major issue is ahead of the feeder breaker in the sub. IE can get pretty large with the slower curves.

Good point about Arcpro simplifying the issues I'm dealing with.

Where is the best place to purchase Arcpro?


Thank you acobb and jghrist

You can start with this link:

http://www.kinectrics.com/en/TechProfiles/ARCPRO.html

Good Chioce!

I didn't find a link to purchase from that site, but I did find it separately.

It looks like HD Electric Company is marketing the software,

http://www.hdelectriccompany.com/hd-electric-products/utility-specialty-products/arc-analysis-software/ARCPRO-Version-2.01.htm

You are correct!

And I forgot to say that when I got my copy of Arcpro, they sent me a CD and after 2 weeks I called to see where my "unlock key" was and they said it usually takes 2 to 3 weeks.....to email a file!

Don't know whats up with that!

FYI, the only electrodes for selection are copper or stainless steel, no aluminum. The stainless steel matches the tables.

Also if you create a test at 8' working distance you will quickly see in the report how the IE drops off.

Good luck with it!

Let us know if it helps.

I assume that you would recommend returning to using IEEE 1584, rather than Arcpro when doing calculations for padmount distribution switchgear, padmount transformers and substations, is that correct?

We use 1584 for switchgear and padmounts rather than the multipliers in Arcpro. We use Arcpro for anthing not enclosed, substations included.