# Three phase balance problem



## saw (Jun 15, 2012)

Hi there,

I am studying Schaum's power book. Some of the problems only have the final answer. Hope you guys don't mind answering my questions. Here is a new one

A three phase balanced load has a 10-ohm resistance in each of its phases. The load is supplied by a 220 v, three phase source. Calculate the power absorbed by the load if it is connected in wye.

I solved it in single phase:

V = 220/sqr root 3 = 127

phase1: I = (127 angle of -30) /10 ohm = 12.7 ang -30

S total = (3) x (127 angle of -30) x ( 12.7 angle of -30) * = 4838.7 VA = 4838.7 W

*The answer in the book is 14520 W*

Thanks for your time.


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## DK PE (Jun 16, 2012)

It's early but your solution appears fine to me and book answer wrong.


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## benbo (Jun 16, 2012)

Don't you have the same answer? Don't you just have to multiply your answer by three to get the total power for all three phases? It comes out the same.

Note- I'm horrible on three phase power and would have likely scrfewed up the part you did. But this makes sense to me.


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## da_souljah (Jun 16, 2012)

Your Answer is correct


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## saw (Jun 16, 2012)

I already multiplied it by 3 in the last equation in S total. Why do I multiply it again?


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## benbo (Jun 16, 2012)

^^^^

Oops. I missed that. Maybe you weren't suuposed to divide the voltage by root three. That's 220 line to line in the problem?

Or maybe they accidentally multiplied twice to get the answer in the book.

Anyway, like I said, I'm horrible at this stuff. I got my PE in Electronics. Your answer is probably right if these other folks say so. If not I'm sure somebody would say so.


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## saw (Jun 16, 2012)

I think Intern and project manager are right. The book answer is wrong. I already contact the author. Hopefully I get the correct answer. If he email me the correct answer and I was wrong, I will post his respond. Thank you all


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## mauldinite (Jun 18, 2012)

Saw, I agree with your answer. I've heard that there are mistakes in the Schaum's power book, so I'm sure this isn't the only one. I don't think that book has been updated in several years so I'm curious what you'll get as a response. Good luck!


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## GUY (Jul 18, 2022)

IP=220/10=22
IL=\sqrt{3}(22)=38.105
P=38.105(\sqrt{3)(220)(COS0)=14520W


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## JideT (Jul 19, 2022)

saw said:


> 4838.7 W


I worked it out too, the answer I got is 4840W


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