# Schaum's Electric Power System-per unit problem 2.11



## electric (Sep 23, 2010)

Can someone please help me to understand this problem;

"3 Phase, Y, 6.25KVA, 220V syn. Gen. has reactance of 8.4 ohms/ph. Using rated KVA and voltage as base values, determine per-unit reactance.

I am coming up with 1.08 pu and the solution is 0.627 pu.

Base Voltage=220/Sq Root 3 =127V

Base Current=[6250/3]/127=16.4A

Base reactance=127/16.4=7.744 Ohms

PU reactance = 8.4/7.744 = 1.08pu

Where is the error?


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## Flyer_PE (Sep 24, 2010)

^I think the error is theirs.

I get: ZBase = (VLL-Base)2/SBase = 220V2/6250 VA = 7.744 Ohm

Zpu = 8.4/7.744 = 1.08

Their answer appears to be 1.08/sqrt3 = 0.626, which is not correct for the problem described.


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## electric (Sep 24, 2010)

Flyer_PE said:


> ^I think the error is theirs.
> Their answer appears to be 1.08/sqrt3 = 0.626, which is not correct for the problem described.


Thanks Flyer_PE.

That's what I though too, but just didn't wanted to jump to the conclusion.


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## BamaBino (Sep 24, 2010)

A third person started a page for errors. I don't know if they are taking updates.

http://www.arie.ws/nasar_electric_power_systems/


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