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Is the apparent power calculation in this text WRONG?

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powersys

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apparent power calculation

The attached example was scanned from a textbook. I tried to calculate S1 but the answer I got was different from the one shown in text. Could someone please help me to verify whether the solution provided in the text is CORRECT or WRONG?

My calculation:

I
= (V1 - V2) / Z
= (240 - 208 - j120) / j10
= -12-j3.2

S1
= V1 x (-I*)
= 240 x (12-j3.2)
= 2880-j768

Question: Why a negative '-' sign in front of I* is required for the calculation of S1? Pls advise.


S2
= V2 x (I*)
= (208+j120) X (-12+j3.2)
= -2880-j774.4


 

powersys

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smxx said:
I think that it is wrong
Err... our answers (S1 and S2) are different. Why?
Do you think the "I" used in your calculation for S2 should be "conjugated"? Thanks.
 

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