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 Post subject: IE Vs Transformer configuration
PostPosted: Tue Apr 23, 2013 10:48 am 
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Joined: Wed Jun 27, 2012 7:01 pm
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Location: Bakersfield
surprisingly found that the Transformer configuration is variable of IE.

While i was using ETAP simulation on 12kV primary voltage, 480 Secondary voltage, for a 500kVA transformer.
I left the all the parameters constant except the transformer configuration.

While i was changing the transformer configuration on the secondary side to solid grounding to delta or No grounding i found the incident energy is changing even the fault current and fault clearing time remained same. Not what is the relation ship between these two later i found this formula in IEEE 1584 where K1 and K2 variables are used. see the attached file for the formula.

Can anybody help me to find how K1 and K2 are calculated in the formula...

Your input is greatly appreciated.... Thanks in advance


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PostPosted: Tue Apr 23, 2013 3:15 pm 
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K1 is a correction factor for the type of equipment you are considering. There is a decrease in incident energy in an open air configuration vs a closed box. The closed box would direct most of the energy in one direction and not be dissipated as fast.

K2 is for grounding: A solidly grounded system will dissipate the fault current faster resulting in less incident energy.

To fully answer the question, these numbers were calculated from a series of arc flash experiments conducted in a lab. The formula was created to fit the observed results from the experiment. It is not derived from anything else, it is just a 'best fit' curve fitting equation.

You only have the options listed in the paper available to you in the fault calculation. Either open box or closed for K1, and grounded or ungrounded for K2.

Hope this answers your question.


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PostPosted: Tue Apr 23, 2013 3:24 pm 
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perfect this is all i need......but i am not sure still what is the reason behind the change in incident energy for same fault current and clearing time in both the cases...... :(

Thanks


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PostPosted: Wed Apr 24, 2013 10:50 am 
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If the Arc Flash occurs inside an enclosure, all the energy will be directed towards the opening of the enclosure. |_| <-- if that is the box, all the energy will be directed out of the top as there is no where else for it to go. This results in a higher incident energy upon the service person. If there is no enclosure (open air), the energy can be radiated freely in all directions, thus eliminating the focusing effect that happens in the enclosure.

As for the grounded vs ungrounded, I can only speculate that a well grounded system will direct the fault current to ground, thus decreasing the amount of energy in the arc. However I am not as certain on this as I am about the enclosure.


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PostPosted: Wed Apr 24, 2013 12:32 pm 
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Location: Charlotte, NC
I would bet the open air vs. enclosure could get a bit more complicated.

There was data for open air and data for enclosed, but there is another possibility.

If you have an enclosure that is large and has doors on three sides with a fixed bottom, top and one side of the enclosure, it would stand to reason that opening one door would be the same as enclosed, but opening all the doors might lie somewhere between enclosed and open air. I bring it up as a possible way to reduce the Incident Energy when testing a system.

We were testing a system where the HRC was a 3. By a combination of using a smaller transformer and opening all the doors of the enclosure, the HRC was reduced to 1 (most of the reduction was in using a transformer 1/3 the size).


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