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 Post subject: Multiple case studies for a generation plant
PostPosted: Tue Sep 17, 2013 7:52 am 

Joined: Tue Sep 17, 2013 7:35 am
Posts: 17
I work in generation, our Arc Flash study came up with various Incident Energy values based on possible line up configurations. Bus Ties in/out, Feeds from UAT's or RAT's, Startup and Shutdown modes. We may have five case studies on the same distribution. The Arc Flash Study summary of Buses indicates the worst case value for each Bus and which Case study the values were associated with. The day to day operators will have no idea as to what the switching line up is for that particular day may be. Do I label the devices with the absolute worst case scenario?


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PostPosted: Thu Sep 19, 2013 11:53 am 
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Joined: Sun Jul 13, 2008 5:00 pm
Posts: 24
If the operators will never know the configuration and the configuration changes regularly, then yes I would use the worst case. However, if the configuration stays the same most of the time and alternates are rare (and result in higher incident energy) then perhaps label "Normal conditions" However, there will still be the problem of advising the operators that the configuration changed.


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PostPosted: Mon Sep 23, 2013 6:44 am 
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Joined: Fri Apr 15, 2011 7:43 am
Posts: 177
Location: Colorado
It is difficult to study ALL the possible combinations that a power plant can configure. I agree with Cutler to use worst case. I am not so sure about "normal" unless it is defined and well documented. We tend to use worst case and maintenance switches that reduce the instantaneous in many of the plants we work in.


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PostPosted: Mon Sep 23, 2013 11:07 am 

Joined: Tue Sep 17, 2013 7:35 am
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Engrick, you bring up another subject that I am unclear on. You mentioned the maintenance switches, does your label reflect the values based on the maintenance mode or do you still post the worst case.


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PostPosted: Tue Sep 24, 2013 3:16 pm 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 831
Location: Rutland, VT
This brings up another good point about the value of an Energized Work Permit and a tailboard briefing. This would allow the documentation of the existing electrical system configuration and if the study is available that could be consulted for AFH under the existing conditions.

I would label the worst case conditions and if they are extreme, then this could provide justification for upgrading the trip devices. For example, if there are breakers that are old with non-solid state trip units (i.e. a GE bkr with a EC-2A device) these could be upgraded to say a Utility Pro device.

As mentioned above, units could have maintenance switches which would reduce the afh as shown by a study. Even with the maintenance switches, I would still label worst case. This brings me back to my first paragraph where the tailboard would discuss maintenance switch and the associated AFH

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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PostPosted: Mon Sep 30, 2013 11:48 am 

Joined: Mon Sep 09, 2013 11:48 am
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Location: Alliant Energy - Madison, WI USA
I also do Arc Flash studies at our generating stations, and run scenarios for the different operating configuations. Our labels show the worst case scenario. That way, Operators and/or Electricians don't need to worry about how the system is configured.


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PostPosted: Mon Sep 30, 2013 12:58 pm 
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Location: Rutland, VT
I also do Arc Flash studies at our generating stations, and run scenarios for the different operating configuations. Our labels show the worst case scenario. That way, Operators and/or Electricians don't need to worry about how the system is configured. - See more at: http://arcflashforum.brainfiller.com/threads/2985/#post-13946

Posting for worst case could possibly make everything Extreme Danger unless worst case is something that can be lived with on a daily basis. If not, then how does an operator and/or electrician perform their functions?

As an extreme example, an operator normally wears non-AR clothing but non-flammable. A motor coupling shears or a pipe breaks and the operator has to rapidly shutdown the equipment at the MCC or Panelboard. However, it is labeled 3.2 cal/cm^2 for worst case operating condition which may be only 1% of the time while 99% of the time it is 0.5 cal/cm^2 In real life would he run to don AR gear or would he just operate the breaker the way he has done for the previous 15 years?

Of course, this whole scenario could loop back to the risk assessment discussions.

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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