# NCEES#530



## electric (Apr 14, 2010)

Has anyone tried solving #530 with MVA method? I can't figure this out with MVA method.


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## CLTEE49 (Apr 14, 2010)

electric said:


> Has anyone tried solving #530 with MVA method? I can't figure this out with MVA method.



Also in this problem I am unfamiliar with ther terms "fault duty" and "X/R ratio". Apparently fault duty is the same is MVAsc. When I first saw this I thought since the transformer and the system have the same X/R ratio that the system would also have a 4% impedence. What if the ratio was different between the two?

Anyone care to explain further?

Thanks,


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## Flyer_PE (Apr 14, 2010)

This thread should help.


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## electric (Apr 14, 2010)

Flyer_PE said:


> This thread should help.


Thanks Flyer, but I was hoping if someone had tried this problem with MVA method. I am getting most of the answers with MVA method but I am little skeptcial to use it till I am sure that I can solve any s.c. problem with this method.


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## Flyer_PE (Apr 15, 2010)

MVA method:

Source is 40 MVA

Transformer is 1MVA with 4% impedance -&gt; 1/0.04 = 25 MVA

Fault MVA = (40*25)/(40+25) = 15.38 MVA

Fault Current = 15.38/(sqrt3*0.48) = 18.5 kA


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