# 3-phase transformer short circuit test: Cram for Exam Vol 2 Question 58



## akyip (Oct 20, 2020)

Hey guys,

I have a question about transformer short circuit tests specifically for 3-phase transformers. This comes from Cram for Exam Vol. 2 question 58.

In this problem, there is a 3-phase transformer given rated as 30 MVA, 130 KV/22 KV, wye-delta. The given short circuit test results are:

Short Circuit Test: 13 KV, 130 A, 110 KW

The 13 KV given in the short-circuit test is not specified as L-L or L-N, but I assume this to be L-L.

The question asks what is the total leakage impedance. In the given solution:

V SC = 13000 V / √3 = 7514 V

Leakage impedance Z = V SC / I SC = 7514 V / 130 A = 57.8 ohms

The solution also states that "the short circuit test uses the high voltage side of the transformer which is wye connected. Therefore, the per-phase voltage is given by V SC" (see above).

My question is: Is V SC the phase voltage measured from the winding during the short-circuit test? Or is it the line-to-neutral voltage during the SC test?

Put another way: if the HV side was delta instead, would V SC = 13000 V?

Thanks for any clarification on this!


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## Rohith (Nov 9, 2020)

akyip said:


> Hey guys,
> 
> I have a question about transformer short circuit tests specifically for 3-phase transformers. This comes from Cram for Exam Vol. 2 question 58.
> 
> ...


Impedance is measured per phase. As the input voltage is wye connected, they divided it by root 3 to get phase voltage


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## akyip (Nov 10, 2020)

Guest Rohith said:


> Impedance is measured per phase. As the input voltage is wye connected, they divided it by root 3 to get phase voltage


I see. So the V SC used for calculating the impedance per phase is the phase voltage during the short circuit test.

Thanks for the explanation!


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## Redy321 (Nov 17, 2020)

akyip said:


> Hey guys,
> 
> I have a question about transformer short circuit tests specifically for 3-phase transformers. This comes from Cram for Exam Vol. 2 question 58.
> 
> ...


Yes, these are difficult questions. As a child, I worked with the teacher personally, he gave me additional lessons. I advise you to do as I did many years ago. I'm an engineer now


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