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Synchronous Generator PPI problem


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#1 Shima

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Posted 05 April 2012 - 06:12 AM

Hi there,
I have a quetions. Problem below is from PPI Sample exam book: A Synchronous genrator is rate for 3MVA, 11kv, and has a power factor of 0.8. What is most nearly the magnitude of the rated current.
Since the problem does not mention three phase, I used " I = S/V. The solution in the book uses " I = S/(VX 1.73) Can some one explain why we using 3 phase formula instead of 1 phase? Thank a lot.

#2 Flyer_PE

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Posted 05 April 2012 - 10:49 AM

^Any machine that size (3MVA) is going to be 3-phase. The largest single-phase machines are smaller than that by several orders of magnitude.

#3 Shima

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Posted 05 April 2012 - 02:33 PM

That makes sense. Thanks for the respond.

#4 robertplant22

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Posted 05 April 2012 - 06:13 PM

Something I've noticed about PPI questions is that sometimes they leave some things open to interpretation.

The NCEES sample questions do not do this; in the NCEES questions there is no room for interpretation because they state everything you need to know about the problem at hand. Hopefully it will be the same during test time.

#5 Flyer_PE

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Posted 05 April 2012 - 07:00 PM

^From my experience, the NCEES sample questions were the closest thing to the actual exam. It makes sense since the same organization generated both the sample questions and the exam. I'm also pretty sure that at least a few of the sample questions are retired questions from past exams.

#6 Shima

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Posted 06 April 2012 - 04:15 AM

You are right, the NCEES questions are the old exam questions. I wish they would have retired more sample questions. Thanks




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