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| Arc Flash Labels - Generators https://brainfiller.com/arcflashforum/viewtopic.php?f=33&t=3706 |
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| Author: | Jim Phillips (brainfiller) [ Sun May 24, 2015 1:49 pm ] |
| Post subject: | Arc Flash Labels - Generators |
If your (client's) power system has emergency and/or standby generators, do you include this scenario on the arc flash label for electrical equipment that can be served both by the utility and the generator(s)? This can also be in the form of multiple labels. We include normal and alternate case incident energy on the label We only include the normal case incident energy on the label It depends Something Else |
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| Author: | wbd [ Mon May 25, 2015 4:38 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
I posted Something Else as I will do worst case. |
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| Author: | Voltrael [ Mon May 25, 2015 5:11 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
Maybe I should have used something else as well. I consider multiple factors, including alternate power sources, and use the highest calculated incident energy value on the label. In one case I am posting a disclaimer though, as the value is quite high (57 cal/cm2) and goes down below 40 in all but one special case that can easily be avoided anyway. |
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| Author: | JBD [ Tue May 26, 2015 6:12 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
We normally include the generator scenario as part of the worst case value reported on labels. Some customers request separate table results, but they still put only one value on the label. Very few, of my, customer's put multiple values on labels, unless it is readily apparent which one is applicable (e.g. AMS switch with pilot light). |
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| Author: | mcqj [ Tue May 26, 2015 7:11 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
SOMETHING ELSE. One worst-case IE AF label is posted. Use of more than one AF label could create a dangerous situation and lead to misinterpretation, accidents, and lawsuits. The AF report always has all scenarios' results which could be consulted and used, but the worst-case results ALWAYS go on the label. Scenarios studied could include utility-provided maximum MVA on the HV side of the incoming xfmr (sometimes that is all that's is provided by some utilities) with min incoming xfmr impedance (-7.5%) and all motor contribution, Same max utility MVA with maximum xfmr impedance (+7.5%) with no motor contribution, and generator alone with no motor contribution. |
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| Author: | robeward [ Tue May 26, 2015 8:39 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
I should have selected something else as we do worst case also. |
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| Author: | JKlessig [ Tue May 26, 2015 9:47 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
Well I used "both" as my proxy for worst case. Our policy is to use the worst case scenario for each location we label. I think to do other wise is foolish. Yes the equipment spends 99% of its life in the normal case, BUT in those occasions where you are likely to have a problem, or to need to" interact" with the equipment, you are also MUCH more likely to be in one of those "alternate cases". In any case, what is your label saying? If you are labeling just the Normal, it is already a "semi worst case", because you are reporting what you think the worst possible IE is under the Normal case, not what it WILL be every time there is an arc flash. Unless you state exactly what the conditions are that lead to that number, [on each label], how is some one supposed to take that label data and know what PPE to use? I would hate to be sitting in the hot seat in court, trying to explain why I but a [Using old style terms] a Category 1 label on a location that had >40 Cal exposure once a week when the generator/ats test happened. And of course, when is an ATS likely to fail? Right when you transfer of course. {And then if you have a closed transition switch.......} |
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| Author: | PaulEngr [ Tue May 26, 2015 2:13 pm ] |
| Post subject: | Re: Arc Flash Labels - Generators |
1 Online (cogen) generator and 2 incoming utility sources. So technically this gives us 7 different scenarios with every combination of utility feeder and generator. But since many would be nearly symmetrical with the bus tie closed, this reduces the number of scenarios to 5 (all online, one utility feeder offline, generator offline, one feeder and generator offline, both utility feeders offline) and since we can't currently operate with just one source that limits the number of scenarios to just 3. If we add a generator especially if it is a different size, we'll probably just have to initially run them all and then pick the couple that matter. |
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| Author: | lovetacycle [ Mon Jun 01, 2015 8:43 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
I would just like to ask, what is the harm in training our techs to wear the correct level of PPE for Normal power situations and then the correct level of PPE for Emergency power situations? The charts for both are included in the arc flash reports, and our techs know when the generator is running. In most cases we have less than 4cal/cm^2 on Normal Power and above 12cal/cm^2 on Emergency Power. That is a huge difference in the level of PPE our technicians need to put on while working on our equipment that is operating on Normal Power 99% of the time. I feel there is a way to do proper training and make it a standard to be able to select the PPE based on the conditions. The only work we allow our techs to perform while energized is basic troubleshooting and operating the equipment. We do not allow racking circuit breakers, pulling MCC buckets, etc.. unless the power is off. Thanks! |
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| Author: | PaulEngr [ Mon Jun 01, 2015 9:16 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
The difference between labelling for "normal/emergency" vs. "worst case" is very simple. It requires more training and more understanding (and an increased likelihood of mistakes being made) if you have multiple conditions. So it depends on your confidence in how likely it is that the process will be followed correctly. One of the fundamental problems that engineers in particular are highly guilty of is that since their training involves figuring out ways to come up with solutions to problems, they often have a hard time looking backwards and figuring out ways that things can fail. Engineers tend to be perpetual optimists. The other extreme tends to be the safety professional, especially safety consultants who can project that basically Murphy's Law applies 100% of the tme. The most popular and advanced safety analysis technique in use today is some form of probabiilistic safety analysis method that starts with the premise that pretty much anything can and will go wrong and that we've got to try to estimate the likelihood of that happening. There are no absolute guarantees of anything in that world which makes it the perpetual pessimist. I'd like to believe that all the techs I work around do the right thing 100% of the time. I'd like to believe that I never make mistakes myself. But I know that is not realistic. I also know that believing that pretty much anything and everything bad can and will happen at any time puts you in a position of not being able to make effective decisions or take any kind of action out of fear of what could happen. This is where we do incredibly stupid and ridiculous things for "safety". 70E does not say "one label". And even if you used one, ultra pessimistic label, that's not to say that you can't have separate procedures overriding the "worst case" label. In fact the task tables in 70E-2015 break down into "PPE required" and "no PPE required" cases whcih are task dependent. And many times especially with double ended switchgear or generators involved, the "worst case" is not the normal or even the most realistic case. So yes, there is nothing wrong with 2 different labels or two different procedures. Just be consistent and be very careful to ensure that the special case gets followed. I just had a case yesterday where I was taking a double ended system offline. The breakers are old Westinghouse feeder breakers (aka S-L-O-W). Without adjusting the mains, the incident energy was 80 cal/cm^2. After adjustment it was 4 cal/cm^2. Quite a difference, and we don't have a 100 ATPV PPE that I could have used. |
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| Author: | JBD [ Mon Jun 01, 2015 11:48 am ] |
| Post subject: | Re: Arc Flash Labels - Generators |
JKlessig wrote: BUT in those occasions where you are likely to have a problem, or to need to" interact" with the equipment, you are also MUCH more likely to be in one of those "alternate cases". The issue is 'interaction that causes an electric arc'. Not all interactions are 'risky' JKlessig wrote: Unless you state exactly what the conditions are that lead to that number, [on each label], how is some one supposed to take that label data and know what PPE to use? If they are qualified they know how to determine the PPE. If they are not qualified, then they should be trained to not be doing what they are doing (110.2(D)(1) and 110.2(D)(2)). If they are absolutely unqualified what good does providing the information do at all? |
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