# Kaplan Afternoon # 27



## HornTootinEE (Jan 22, 2011)

#27 on the Afternoon portion from the Kaplan book:

"Two Single Phase XFMRs are connected in parallel with their primaries connected to a 25 kV supply. Transformer 1 is rated at 600 kVA, 25,000/600 V and Transformer 2 is rated at 500 kVA, 25,000/610 V. The equivalent impedances are 0.02+j0.05 pu and 0.02+j0.06 pu. respectively, based on on 600 kVA, 25 kV. The no load circulating current is:"

I can do the problem, question is, in the answer to calculate Ibase Kaplan uses Sbase/(SQRT(3)*Vbase). Considering these are single phase transformers in parallel, not an open 3-ph configuration, wouldn't Ibase be Sbase/Vbase ?

I have found other errors in the Kaplan answers. Even to the extent the work is right, and the calculation was incorrect. Have others found this with Kaplan as well?

Thanks in advance.


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## Flyer_PE (Jan 22, 2011)

Kaplan has its fair share of errors. If you're working on a single phase problem, the square root of 3 shouldn't appear anywhere. The reason they get away with it is that they are only calculating a base current. If they were working directly with the actual values, they would arrive at the wrong answer.


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## knight1fox3 (Jan 24, 2011)

Flyer_PE said:


> Kaplan has its fair share of errors.


Agreed. There was a helpful thread from studying for the Oct. 2010 exam which summarized most of the errors found in the Kaplan book (thanks Cableguy). This may help to keep a certain level of sanity when working these problems.


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