I am currently looking into evaluating the incident energy results provided in ArcPro vs. SKM. Seems as if SKM is much more conservative with their results, although I have done hand calcs to verify that they are using IEEE 1584 to the T. I can only assume SKM and Easy Power both will provide similar answers as they both use 1584 for the calculation. I am not sure what calculation ArcPro uses, but it is recognized by OSHA as an acceptable means of calculating incident energy. Does anyone have experience with ArcPro? I am hesitant to use it and I am amazed that OSHA will recognize both IEEE 1584 and ArcPro when the results are so vastly different.

I believe most of the major S/W companies use IEEE 1584 three phase models. However, Arc Pro was developed by Ontario Hydro and is based on a single phase model. Although an arc flash may begin as a single phase event, due to the conducting plasma it can quickly escalate into a three phase event in which case the IEEE model would provide more conservative results. However, modeling transmisson and distribution lines where conductor spacing would make the arc escalation unlikely, a single phase model i.e. Arc Pro model may be more appropriate.

Thanks Jim,
At the time I had wrote that posting I had not realized that ArcPro based their calculations on single phase in air and not three phase bolted. How confusing! In either case, I did find in ArcPro's help file an adjustment multiplier of 3.7 - 6.5 times the slg fault to convert it into a bolted 3ph in a box fault. Clouds the issue even more. I think I am going to stick with 1584 as I am familiar with it and doesn't require a range of multipliers to apply it to a three phase bolted fault. Thanks for the feedback! Have a great Thanksgiving!

Arc Flash Hazard Analysis Engineering Specification

Interesting we are debating the software's capabilities for "doing the arc flash calculation" when it is really the engineer using the software that is doing it, and in a lot of cases is the engineer qualified and competent to be doing the analysis. Let me ramble on a bit, we need an engineer that first understands Power System Design, and Protection & Coordination, then we layer in Arc Flash Hazard Analysis.

There are quite a few software packages out there:

SKM
ESA Easypower
ETAP
EDSA
ArcPro
Cyme
Aspen
Excel Spreadsheets
Duke Heat Flux
? I probably missed some, if you know of others please reply.

All of these are software tools for the design engineer. Some of them only do the arc flash calculation, and no more. So I would questions how in depth your arc flash hazard analysis really is, as my opinion is you have to not only do the AFHA, but you should be able to consider "Safety by Design" techniques to consider how to reduce the calculated incident energy.

Oh, and what about have an engineering specifciation for this analysis? I see a lot of $$$$$ been wasted by Owners (all industry sectors in Canada), as they ask the engineer for the study and it's like a blank cheque. Engineers are learning how to do this calculation, how to run scenarios, how to complete "Safety by Design." As a client you should provide the engineer with a specification, even if it is one page, so that you control $$$$. You pay for what you asked for, not what they gave you.

These studies if not controlled by the Owner can be in the ten of thousands fo dollars to hundreds of thousands (depending on the power system complexity). Yes some of them should be costly, but not all of them.

You can template a lot of the front end single lines, then work from these to complete multiple studies, a sample as was the case in my previous employment where we had 2400 electrical services, and two 100MW+ power plants.

Besides all of that did you check, or pre-qualify the engineer doing the work? If you don't know them or their capabilities, did you get a resume, examples of previous reports issued. Where the reports thorough, but not a book?

As well did you get the study "stamped" by the Professional Engineer in the Province or Territory that your facilities are in? My Professional opinion is that you should have this "safety" related analysis signed by a P.Eng. in Canada.

Did you put the Flash Protection Boundary and incident energy information on your Single Line Diagram? Did you get the engineering to complete a Arc Flash Hazard Analysis Data Sheet for the calculation, a record of the key assumptions made in the configuration of the "arc flash module" or in "the various locations within the software" where you configure the variables for the calculation.

Sorry for running on, but my opinion is that before we over analyze the software's use of IEEE 1584 etc... we should do a detailed review of the Professional Engineer that will be using the software tool. After all the software is just a software tool, the intelligence, experience, knowledge, expertize, is with the Professional Engineer who will be using the tool, and of course he/she should understand what methodology and what it is been used (i.e. IEEE 1584, 70E, Lee, etc...).


Regards;
Terry Becker, P.Eng., C.E.M.
CEO, Senior Management Consultant
ESPS Electrical Safety Program Solutions INC.
terry.becker@espsi.ca
403-465-3777

Terry,
You are quite correct, there are many very well qualified engineers performing studies and unfortunatley the opposite is also true. A good spec and review of engineer's qualifications is very important. Since the industry has not yet standardized on a specific format or scope of services and this whole subject remains confusing for many, I have seen many companies taken advantage of.

The good news is the majority of people I run into that perform studies and are involved in electrical safety are quite good and use the utmost care. They should all be commended for taking arc flash studies in the proper direction.

This original thread was started assuming well qualified people are conducting the arc flash studies and then sorting out which software to use. (like good carpenters discussing the best hammer to use) But as we all know, regardless of s/w, the study is only as good as the person conducting it.

So....where do we go from here?

As a new member of this forum, a practicing utility engineer for 28 years who is extremely concerned with the standards promulgated by the NFPA and the IEEE (suggestions), I have some thoughts to share for comments. We have NESC 2007 which requires an "assessment" be done by 1/1/09 and the workers be protected to the level of the hazard, yet it contains coarse and, I believe, not practical guidance to comply with the standard. As you will be aware if you are in the industry, these workers are exposed to voltage sources above and below 1000 volts.

The NESC, at below 1000 volts, only gives us the guidance that we should use "engineering controls", comply with work practices in part 4 and have technicians wear a PPE rated for 4 cal/cm2 clothing. How about face protection from a 480/277 volt arc at the secondary terminals of a 1500 kva pad transformer?

We also must consider the reality that most utility system buses have a higher L to G fault duty as a result of the delta/wye transformer connection and with proper work practices will most likely NOT progress to a three phase fault.

The only reason I can think of for this approach is that the writers of the NESC recognize that the utility industry practices are most often overseen by PE's responsible for determining and mitigating the hazards, as well as, compliance with the standards.

All of us in the industry know that live line work always has its hazards and worker safety should always be top priority. My fear is that these new standards, eventhough some are "recommendations" when relied on in a legal proceeding will be considered industry practice and therefore " jury law".

As a lineman for eight years prior to completing my engineering degree, I was exposed to a 4160 arc flash on a pole (my fault) with minor injury, but during those few seconds with what appeared to be the sun brightly in my face, thought I might not survive the incident. The burns healed, the hair and eyebrows grew back, and I threw the burned tee-shirt away.

All of that said, I am concerned with the cost to my clients in their efforts to comply with what I believe to be an extremely vague standard as well as the legal implications arising because this will be considered standard industry practice. After all it is a part of the current version of the NESC.

Sorry for the rambling, but this standard has the probability, if not already, of becoming the largest multi-headed monster to ever hit this industry!

BTW...I intended for this to be placed in the General Discussion category.....sorry, my bad!

Would love to hear your comments! Alan

Just a few observations:

i) it would be difficult to perform linework with the arc flash protection PPE. I suspect the utilities will bow out from this, as they have also chosen different than NEC standards for grounding etc. There is some justification as a pole top event would be different than what would be expected in front of metal clad switchgear, but also they might do this simply because they can.

ii) I have seen some of the wanton engineering described by Terry B, completed by arc flash consultants with an open check book. But I think Terry could benefit from the experience of trying to complete a consulting project to a customer spec: given the opportunity, most customers specify 'just the answers' without any time commitment for analysis. Especially in arc flash anaylsis that includes mitigation through new system protective settings, the path is often obscured and there is little hope that a proposing engineer will know all the previous history of a system.

If you don't know diamonds, know your jeweller. If you don't know engineering, cultivate a trustworthy relationship with your consultants.

ArcPro vs. SKM

As I understand it, IEEE 1584 equations are based more on empirical formulas developed from arc tests at lower voltages (i.e. 480V). The results of these equations are less accurate at higher voltages (mostly in the conservative direction). ARCPRO is a physics based model of the arc and tends to be more accurate at the higher voltages.

jleman, do you or anyone in this formum know of any papers written about Arc Pro? i.e. how was it modeled, where did the data come from etc.?

If this is one of the programs used for utilities it would be nice to have something more than a "black box" and not knowing what's inside.

Thanks!

1584, ArcPro, Duke, Sask, etc.

Like other utillities, we're trying to figure out which calculations and software model best approximates the potential arc flash energy in the various energized work scenarios we encounter. Whether you have that professional engineer designation or not, many of us are compelled to dig deeper and ask many questions about estimating the arc flash hazard and then figuring out what you're going to do about it. It's pretty overwhelming when you consider all the variables.

At the moment, I'm limiting my focus on overhead distribution just to get my arms around the arc flash hazard on this aspect of our system. Okay, so we think about the overhead system, live line work methods, protection settings, human factors, PPE, distances, etc. as we try to decide how we are going to go about our analysis to consider the hazard to workers. I go to IEEE 1584 and Duke Heat Flux, run the numbers and find incident heat ranging from 2 to 120 cal/cm2 on our 25 kV system. But then, I realize I also need to consider that 3 phase tap/dip off to an underground live front 3 phase transformer or switchgear in the analysis. Oh, and perhaps I need to consider when feeders are paralled, re-configured, IPPs connected, large motors, etc. I could go on and on about the scenarios until your head spins. The variety of scenarios and system conditions lead me to considering worst case when assessing the hazard.

What seemed clear to me when I began to develop an understanding of the arc flash hazard is that protective device clearing times play a major role in reducing the energy. Going to a low-set instantaneous setting of the breaker seems like a simple concept and control barrier which would benefit workers under live line work. But then you start talking to operations folks who raise many concerns about public safety and managing more outages. This is a big deal for the utility. Suddenly we find ourselves on a tight rope attempting to weigh the trade-offs of worker safety versus public safety.

We have 300 lockouts per year on feeders under live line permit, where the outage was unrelated to the worker. If we change breaker/recloser protection for live line and then downstream fuses don't coordinate, we know the incidental outages will increase, perhaps double or triple. Now how do we mitigate the unexpected outages, to what extent do we patrol, what makes it safe to re-energize? Can we reduce the outages through careful selection of the protection settings? What do I do about ground fault relays? Should we limit consideration to phase and negative sequence settings with respect to arc flash on distribution? So many questions, so many stakeholders to satisfy and sell on the solution I've come to in my own mind.

Even if we had the perfect model to estimate the radiant and convective heat, this would not help me figure out all the operational impacts. Arc flash mitigation seems to lead us to an enormous change management issue for the electric utility.

Regardless, I want to keep moving forward, exchange information, understand what other utilities are doing. I'm for changing settings for any live line work, but I've got other people to convince who have a very different position.

I just finished a job with the utility crews working 12.4KV live. All the crew have a normal FR uniform of Level 2. They dress with gloves and sleeves as needed.

The first question I would ask is if Utility Linemen fall under the NFPA70E regulations? Utilities are exempt from following the NEC. They could very well be exempt from NFPA as they constitute special conditions as a utility and linemen receive specific training and supervision.

My first thought is that you maintain the high, longtime setting to avoid nuisance tripping. When you have to work on the line you can reduce settings. Often utilities have reclosers with 2 to 5 recloses after a fault to clear the line. Its typical to disable the recloser when work is being performed. I would be pushing for longterm upgrades to install maintenance switches on reclosers and station breakers that can easily be turned on and off when work is being performed.

As far a PPE, I think you are limited to Level 2. The suits get way to bulky for a lineman at Level 3 and 4.

new program for 600V and below

There should be a new program coming out soon (this fall), just for low voltage, that should help the fact that we have more simple low voltage systems needing studied, than we do power systems studies engineers with the right training to do these systems. Those of you in consulting or needing another basic tool... stay tuned.

[url="http://www.arcadvisor.com/arcflash/arc_flash_analytic.html"]Arc-Flash-Analytic v 2.0[/url] software tool has been developed based on IEEE 1584 Guide for Performing Arc-Flash Hazard Calculations as an easy to use and comprehensive instrument for calculating arc incident energy, flash protection boundary and risk category required by N.E.C and OSHA when work is to be performed on or near the energized equipment. Please have a look on [url="http://www.arcadvisor.com/arcflash/afa_v1p1_calculation_example.html"]calculation example[/url] and don't hesitate to ask me if you need more information.

Sincerely, Michael Furtak

Anyone hear of MilSoft? I have heard there name but know nothing about them.

Although an arc flash may begin as a single phase event, due to the conducting plasma it can quickly escalate into a three phase event in which case the IEEE model would provide more conservative results.

We are trying to learn more about this also. Does anyone have experience with this program and how does it compare to the other utility programs?

Milsoft / WindMil / Arc Flash Calcs



Milsoft has an Engineering Analysis (EA) program called WindMil that is popular w/ electric cooperatives. They have recently added the IEEE 1584 calcs to the software. The beauty of this is if you already have your distribution system modeled in the software, you can now perform the arc flash calcs directly in your system model.

I've been working as a beta tester on it. So far, the Milsoft calcs match the IEEE calcs I've been doing by hand.

http://www.milsoft.com

For utility distribution systems, shouldn't the calcs match NESC tables or ArcPro calcs instead of the IEEE-1584 calcs?

Utility Arc Flash Study Calcs / NESC

My impression has been that the utilities don't like the tables, as they are a bit simplified given the broad range of distribution system configurations. All of these calculations are in their infancy .... how can anyone justify stating that the use of the tables is an accurate method for every utility to address the issue? None of the calc methods even accurately model the incident energies over the ranges of voltages on a typical distribution system.

Both ArcPro and the IEEE method are industry-recognized methods, and there are others. They all have their strengths and weaknesses. It's up to the engineer to recognize this and to make sound judgements in their analyses.

The "spirit" of the NESC guidelines is for utilities to do their due diligence and determine the best way to protect its employees from workplace hazards. Its not just to "follow a table, buy some clothing, and put some stickers on your stuff". In my case, I believe that a combined use of two industry-recognized calculation methods (IEEE & ArcPro) will best suit my company's needs.

Cooperative Research Network (CRN) just released a report on Arc Flash Calculation Case Studies for Distribution Systems. It's definitely worth a read.

Is there a way for non-NRECA members to obtain this report?