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 Post subject: 15 KV Padmounted Switch Arc Flash Analysis
PostPosted: Tue Jan 26, 2010 11:38 am 
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I am looking for some opinion on how a medium voltage padmounted switch should be approached related to an Arc Flash analysis.

I believe that they would be considered as 'switchgear' with an 'Arc in Box Arrangement'. My concern is that modeling them in this way results in a category 0 in this particular system because of the fast clearing times of instantaneous overcurrent relaying and current limiting fuses upstream. I'm concerned that this low hazard rating may be incorrect or misrpresent the hazards.

I know that these switches are 'dead front' construction but they also are bushing well types that include load break elbows that are also designed to be disconnected with a hotstick.

Maybe I am just overly concerned having worked in electrical maintenance in process industries but I am afraid that the low category for this particular situation would be misintepreted and generalized for other medium voltage switching operations.

Any opinions would be welcome.


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PostPosted: Wed Jan 27, 2010 2:38 pm 
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Sorry, guy I would need more data to help you with your issue.


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PostPosted: Wed Jan 27, 2010 9:37 pm 
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You should never generalize a specific IE calculation for other medium voltage switchgear situations.

Are you making an IE calculation or determining the category from the 70E task tables?

If you are calculating IE, why in particular do you think that the IE calculation would be incorrect. If anything, I would think that being deadfront would make the calculations conservative. The working distance assumed in IEEE Std 1584 doesn't consider using hotsticks. IEEE Std 1584 also assumes than any 1-phase fault will develop into a 3-phase fault. This would be unlikely with dead front padmount switches.


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PostPosted: Thu Jan 28, 2010 9:03 pm 
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I agree with you that an arc flash rating is indeed, specific to that piece of equipment.

My worry is that others may generalize that work on this type of equipment is not of concern and become complacent.


You also do have a valid point about the IEEE 1584 standard assuming a three phase fault.

The more likely issue that i could see might be a problem with a cable or a load break elbow when placing it in a parking stand. This would most likely be a single line to ground fault.


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