# Q 513, 530, 540



## Ahmed S. (May 10, 2020)

Hi everyone,

I am trying to figure out how to select the right S base, in Q 513 they used 100 MVA as a base and there is no mention to this number any where in the question , why they did not chose the base of the transformer 7.5 MVA to be the same as for the transmission line. In Q 530 they chose the transformer MVA to be the S base which is 1000KVA or 1 MVA  and  in Q 540 they chose the Generator MVA as the S base not the MVA of the transformer and they did not chose 100 MVA as in Q 513, I want to make sure to chose the right S base in the PE exam, any help would be much appreciated.


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## LyceeFruit PE (May 10, 2020)

@Ahmed S. I assume this is from the NCEES practice guide, 2017 edition?


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## Ahmed S. (May 13, 2020)

LyceeFruit PE said:


> @Ahmed S. I assume this is from the NCEES practice guide, 2017 edition?


Yes that is correct


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## Sthabik PE (May 15, 2020)

@Ahmed S. You can choose transformer 7.5 MVA as Sbase and do the calculation. You will get the same result.


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## Ahmed S. (May 15, 2020)

OK thank you for your answer


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