# Comparing new NCEES #135 and #522 (Power)



## indy-engineer (Apr 21, 2009)

Am I correct to assume you set up the equations differently if you're talking about a generator compared to a motor regarding how you set up the equation to find the terminal voltage and internal voltage? It looks like we added the (reactance X current) in one situation and subtracted it in another. If I'm way off, please let me know. I'm trying to see what the difference is in these two problems.

Thank you, as always!


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## Flyer_PE (Apr 21, 2009)

The setup is actually the same. The difference is that the internal voltage for the generator will be greater than it's terminal voltage. For a motor, the terminal voltage will be greater than the internal voltage.


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## indy-engineer (Apr 21, 2009)

That's exactly what I needed to know. Thank you!!!!


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## niurou (Apr 21, 2009)

Flyer_PE said:


> The setup is actually the same. The difference is that the internal voltage for the generator will be greater than it's terminal voltage. For a motor, the terminal voltage will be greater than the internal voltage.


I'm sorry, this is not exactly right.

If power factor is leading,

for generator, the terminal voltage can be actually greater than the internal voltage.

for motor, the internal voltage can be greater than terminal voltage.

motor: V=E + jXI or E = V - jXI

Gen: E= V + jXI or V= E - jXI

It's a little counter intuitive. But we are deal with vectors, when you see E = V + jXI, in term of magnitude, E is not necessary greater than V.

arty-smiley-048:


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## niurou (Apr 21, 2009)

see the attached picture.


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## indy-engineer (Apr 22, 2009)

Thank you. I think that makes sense.


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## BamaBino (Mar 1, 2011)

niurou said:


> see the attached picture.


Does anyone have the picture that he was referring to?


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## dianevp (Mar 1, 2011)

I don't see it either.


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