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 Post subject: OSHA 1910.269, ArcPro, EasyPower, Cyme, etc.
PostPosted: Sun Dec 07, 2014 9:19 am 
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Location: Rutland, VT
As most everyone is aware of OSHA issued new 1910.269 rules for utilities and arc flash. A table was provided in Appendix E for selecting a calculation method. For utilities trying to determine a reasonable estimate of incident energy on their overhead systems, particularly distribution where voltage is less than 15 kV, the choice seems to be IEEE 1584 for single and three phase open air faults while ArcPro seems to be only recommended by OSHA for single phase open air faults.

I am not sure about all the analysis programs out there but here seems to be what I have found for 2 of them in looking at using them for single or three phase open air faults:

EasyPower - after setting up buses as Open Air type the only way to perform a SLG fault is to go into Advanced features and utilize NFPA 70E 2009 Annex D.8 Hazards by checking apply to Open Air Buses. There is then a multiplier used for LL or 3ph faults. However, the NFPA 70E 2009 Annex D.8 method is not in the OSHA table of recommended methods.

Cyme - The write up I have from Cyme on the arc flash module indicates that for transmission and distribution analysis, the only standard to use is NESC. It appears that Cyme uses the results from faulting a bus to go to the NESC Tables, look up voltage, fault current and clearing time to return a cal/cm^2 system to be used. This is also not a method in the OSHA table.

Therefore, with only those two software packages that appear to use something other IEEE 1584 for the open air utility type faults at my disposal to use, it seems they can't be used to meet OSHA.

That leaves me with the other software package I have is with ArcPro. This OSHA says is recommended only for single phase open air below 15kV but is ok for above 15kV for single phase and 3 phase (with multipliers). Reading the Preamble to OSHA it appears that they feel ArcPro would be overly conservative for 3 phase faults using the multiplier.

So, with those constraints, is it unreasonable to use ArcPro with a multiplier for 3 phase distribution systems (4.16kV to 13.8kV) even though it may be overly conservative? I think it would still meet OSHA requirement of a reasonable estimate of incident energy. The other thing to consider is that a 3 phase open air fault on a distribution system is not a common occurrence.

Look forward to a discussion and if people that use other software (SKM, EDSA, ETAP, etc) can report on what those systems use for open air faults at utility voltages, that would be great.

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www.workplacesafetysolutions.com


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 Post subject: Re: OSHA 1910.269, ArcPro, EasyPower, Cyme, etc.
PostPosted: Mon Dec 08, 2014 8:10 am 

Joined: Mon Feb 22, 2010 10:24 am
Posts: 21
NESC takes the approach the short circuits on overhead facilities will be line to ground or line to line and that a three phase bolted fault is not likely to occur. I believe that is why they used ArcPro to establish the tables. My understanding is that ArcPro is produced from empirical data and is appropriate for single phase faults. IEEE 1584 is similarly based on empirical data but with three phase bolted faults. IEEE 1584 testing was based on equipment types and is not appropriate for medium voltage power and high voltage power systems in general. SKM PTW has two options for calculating arc flash on these systems. 1. Use the NESC method which calculates short circuit current and clearing time and does a table lookup from NESC tables. 2. Use Ralph Lee equations for three phase bolted faults.

If you consider single phase faults to be appropriate then the NESC method (which OSHA 1910.269 is based on) should be used. If you consider that a three phase bolted fault should be considered then I think you must use Ralph Lee equations or the multiplier for ArcPro. I don't know the derivation of that multiplier so I am not sure how appropriate that is.


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 Post subject: Re: OSHA 1910.269, ArcPro, EasyPower, Cyme, etc.
PostPosted: Mon Dec 08, 2014 2:24 pm 

Joined: Wed Jun 24, 2009 4:45 pm
Posts: 41
Location: WA State
wbd wrote:
So, with those constraints, is it unreasonable to use ArcPro with a multiplier for 3 phase distribution systems (4.16kV to 13.8kV) even though it may be overly conservative? I think it would still meet OSHA requirement of a reasonable estimate of incident energy.


You are asking if your suggested method would meet the OSHA requirement. I believe your answer is provided in OSHA Table 3 as "N", "Not acceptable; does not produce a reasonable estimate ...". If it were okay, as you are desiring, then the table would have used "Y-C" to indicate a calculation method that is "Acceptable; produces a reasonable, but conservative, estimate ..." or it would have referenced note 4. The table does not refer to either, so seems like a stretch to argue that this recommendation would meet OSHA requirement of a reasonable estimate.


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 Post subject: Re: OSHA 1910.269, ArcPro, EasyPower, Cyme, etc.
PostPosted: Mon Dec 08, 2014 2:59 pm 

Joined: Wed Jun 24, 2009 4:45 pm
Posts: 41
Location: WA State
I would think it would be more reasonable to reference the NESC lookup method for overhead, which is essentially like using ArcPro, except that you are using the NESC's pre-calculated table of values. You just need to double check that the parameters being used by the NESC table are reasonable for your application.

wbd wrote:
IEEE 1584 testing was based on equipment types and is not appropriate for medium voltage power and high voltage power systems in general.


I'm using a distribution software called SynerGEE that uses the IEEE 1584 method for overhead and underground, single phase and three phase. We have pad-mountend live front switchgear and also some livefront pad-mounted transformers. In this case, I think the three phase IEEE 1584 method is the most appropriate choice. I've decided to use IEEE 1584 across the board, for underground and overhead. I also think it is the most appropriate choice for calculating the incident energy of racking breakers within metalclad switchgear, which is common for medium voltage power systems.


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 Post subject: Re: OSHA 1910.269, ArcPro, EasyPower, Cyme, etc.
PostPosted: Tue Dec 09, 2014 8:33 am 
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IEEE 1584 empirical formula has a stated valid range of 208 V to 15 kV 3 phrase, 50-60 Hz, 700 A to 106 kA, 13-152 mm conductor gap. Outside of this range, IEEE 1584 offers the Lee theoretical equation only which is known to be valid only up to about 600 V. IEEE 1584 cannot be applied with even a lot of medium voltage switch gear (gaps are too wide), even within the stated range up to 15 kV. It does not implement single phase arcing at all.

The gap limitation eliminates a lot of live front and dead front equipment from consideration. The lack of a single phase implementation eliminates most overhead equipment. It's not a bad choice for racking interrupter gear where everything is open but since it assumes 3 phase arcs and at least theoretically metal clad switchgear reduces all arcing down to single phase line-to-ground only, it doesn't really work for that type of gear either. ArcPro (or tables in NESC) is suitable specifically for overhead open air conditions in particular but not enclosed equipment and the notes to the tables make this clear. The low voltage (<1 kV) table does cover this type of equipment. Thus for medium voltage metal clad switchgear really there isn't an appropriate model and you are either going to take IEEE 1584 values and "hope" they are right, or else take ArcPro values and apply the recommended multipliers, again, "hoping" for a good result.


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 Post subject: Re: OSHA 1910.269, ArcPro, EasyPower, Cyme, etc.
PostPosted: Tue Dec 16, 2014 10:01 pm 
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PaulEngr wrote:
Outside of this range, IEEE 1584 offers the Lee theoretical equation only which is known to be valid only up to about 600 V.


The IEEE guide is indeed recommending Lee's equations from [B19]* for cases where voltage is over 15 kV, or gap is outside the range of the model (or beyond the 13 to 152mm range). I have reviewed the original Ralph Lee's paper and I don't quite understand why you believe the equations are not applicable above 600V. Please elaborate.

* - IEEE 1584-2002 Annex F. Bibliography [B19]: Lee, R., "The other electrical hazard: electrical arc blast burns," IEEE Transactions on Industry Applications, vol 1A-18. no. 3, p. 246, May/June 1982.


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