Our large, facility?s power distribution has undergone an ARC/FLASH analysis. Corrective measures have been taken, and one lines have been updated. As future requirements alter loads on our system, we?ll need to have the analysis up-dated. We do not know how to determine what indicates the need of an up-date. Obviously, major changes, but not every minor item. Is there a ?rule of thumb? starting point? (KVA., motor horse power, specific type of load, etc)
Arc/flash analysis
- Thread starter Don S.
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StephenSDH
Senior Member
- Location
- Allentown, PA
It is recommended to reupdate the survey every 5 years.
I attached a excerpt from the NFPA 70E.
It basically says the survey should be updated for major changes, and that analysis is not require 240V and below if supplied by less then 125kva transformer.
If you are installing or removing equipment that doesn't meet the above criteria for being exempt, then you might want to rerun the study just to insure the calculations come out close to the same. I would consider a major change changing the way equipment is fed, like adding a generator or changing overcurrent protection. Installing a machine will not greatly effect other sections of your plant unless it stores power which can be put back on the line when a fault occurs (like a large motor or capacitors). It is more modifications to distribution equipment 125kva or greater and/or greater then 240v that will change arc flash results.
I attached a excerpt from the NFPA 70E.
It basically says the survey should be updated for major changes, and that analysis is not require 240V and below if supplied by less then 125kva transformer.
If you are installing or removing equipment that doesn't meet the above criteria for being exempt, then you might want to rerun the study just to insure the calculations come out close to the same. I would consider a major change changing the way equipment is fed, like adding a generator or changing overcurrent protection. Installing a machine will not greatly effect other sections of your plant unless it stores power which can be put back on the line when a fault occurs (like a large motor or capacitors). It is more modifications to distribution equipment 125kva or greater and/or greater then 240v that will change arc flash results.
charlie
Senior Member
- Location
- Indianapolis
If the serving electric utility has a major rebuild or the primary distribution is switched from one substation to another, you may need to do the calculations again. Keep in mind that a substation further away may reduce the amount of available fault current but increase the incident energy. On the other hand, a closer substation could have more available fault current than your gear can handle. If a transformer is replaced and it has a different impedance, the same scenario exists. 
richxtlc
Senior Member
- Location
- Tampa Florida
You should periodically check with the utility to see if the available short circuit current has changed. Many utilities will just give you the infinite bus value, if they do ask them for the latest engineering values on your feeders. Bear in mind that routine switching and maintenance on the utilitie's transmission and distribution system can change the value of the short circuit current on a daily basis. So your study should include values at +/_ a percentage (25%) of the value that the utility gives you. This will enable you to determine the worst case scenario, which will probably be at the lower value, and determine what level PPE should be worn.
Arc/flash
Arc/flash
We are not so concerned about the utility, as we take our feed from them at 13.8KV from a dedicated transformer in their substation. Our plant distribution is 13.8KV to 45 substations with secondary voltage of 4160,480 and 208. Our concern, is knowing when we should get a new survey on a particular substation.
Arc/flash
We are not so concerned about the utility, as we take our feed from them at 13.8KV from a dedicated transformer in their substation. Our plant distribution is 13.8KV to 45 substations with secondary voltage of 4160,480 and 208. Our concern, is knowing when we should get a new survey on a particular substation.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
New survey would be needed if:
you add equipment and need data for those pieces of equipment;
if the contribution changes, whether it be from the utility, gens or motors;
if you change the OCPD settings;
or if the path of distribution changes significantly, such as changing the normal vs. alternate route.
These changes will either raise or lower the PPE values required, sometimes unexpected or non-intuitively in the way they propagate through the distribution.
you add equipment and need data for those pieces of equipment;
if the contribution changes, whether it be from the utility, gens or motors;
if you change the OCPD settings;
or if the path of distribution changes significantly, such as changing the normal vs. alternate route.
These changes will either raise or lower the PPE values required, sometimes unexpected or non-intuitively in the way they propagate through the distribution.
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