# page 54 of Ugly's Electrical References



## BamaBino (Jul 19, 2011)

I'm working the problem on page 54 of Ugly's Electrical References.

I assume the voltage of the transformer secondary is 480V (same as the primary).

Is that correct?


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## DK PE (Jul 19, 2011)

BamaBino said:


> I'm working the problem on page 54 of Ugly's Electrical References.I assume the voltage of the transformer secondary is 480V (same as the primary).
> 
> Is that correct?


I don't have that reference but I would assume the secondary voltage is 480V and therefore you can calculate the fault current with an "infinite primary". I don't see any reason the primary voltage is needed.


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## Complex Imaginary (Aug 3, 2011)

DK PE said:


> BamaBino said:
> 
> 
> > I'm working the problem on page 54 of Ugly's Electrical References.I assume the voltage of the transformer secondary is 480V (same as the primary).
> ...


(agreeing with DK PE)

For this problem, it is safe to assume that the voltage on the secondary is 480V. In the diagram, they only give one voltage and since all the circuit elements are on the secondary side (fuses, short ciruits, feeders) the only thing you can do is use the 480V shown. If this were a PE problem, it could be argued that it would be just a tiny bit unfair to force the testtaker to make that assumption, even though it is relatively obvious. ...teeny tiny bit unfair ... skosh-like. I got it: bantam unfairness.


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## BamaBino (Aug 8, 2011)

I'm working this problem using the same method that I used for the Fault problems in NCEES2009_Sample_exam.

Below is my work for finding Fault X1 (before considering the motor).

I got the correct answer but don't feel real confident. Would y'all verify it?

Thanks.


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## DK PE (Aug 8, 2011)

BamaBino said:


> I'm working this problem using the same method that I used for the Fault problems in NCEES2009_Sample_exam.Below is my work for finding Fault X1 (before considering the motor).
> 
> I got the correct answer but don't feel real confident. Would y'all verify it?
> 
> Thanks.


Take another look at the equation you are using for base impedance... under test pressure be sure you can figure out per unit for single phase and three phase. In this case, it doesn't toss the answer off very far but you never know...


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