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 Post subject: Calculation of Incident energy at secondary of transformer
PostPosted: Mon Aug 24, 2009 8:10 am 
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Joined: Mon Dec 08, 2008 7:52 pm
Posts: 8
I have a 250 MCB as the primary protection which supplies a 225KVA, 5.27% Z, the transformer is 480 to 240. There is a secondary fused switch with 250V FRS 200A. I am questioning the incident energy on the secondary side between the bushing and the actual disconnect switch. I am assuming the 250 MCB will determine the incident energy. Any thoughts on calculating this value? Thnaks for reading my post.


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PostPosted: Sat Sep 12, 2009 1:14 pm 
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Joined: Sun Aug 16, 2009 8:42 am
Posts: 184
Location: Lawrenceburg KY
A really rough estimate on the secondary and the load side of the fused switch could be as high as 85 inch AFB, 12 cal/sm2 @ 18inch CAT#3@18" assuming a SC of 8.6ka.

With my generic data the secondary SC could last a long time before tripping the breaker on a HI trip setting.

However, if you have a low trip level the game changes. I get a 6" AFB .03 cal/cm2 @18" CAT0 @18".

The breaker type and trip data is very important in determining your actual energy levels. The other problem is your transformer inrush which I suspect will probably be the problem to overcome.

I am guessing your trip level is going to be high because of that.


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PostPosted: Sun Sep 13, 2009 10:37 am 
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Joined: Mon Dec 08, 2008 7:52 pm
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Thanks for the reply

My details which were not many is at a plant I am going to in mid Ocotber. I plan to get more info I will post as I get it.


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