X/R ratio impedance calculations - Cram for Exam Vol.3 Question 76

[akyip]

Hey guys,

I have a small silly question about X/R ratio formulas for calculating impedances, from Cram for Exam Vol 3 Question 76.

In this problem, two per-unit impedances are given on the same MVA base. The solution then directly uses some X/R ratio formulas and math manipulation to determine the overall system X/R ratio.

If the 2 per-unit impedances were on different KVA bases, they would have to be converted to a common KVA base before carrying out the X/R ratio mathematics in the solution... Correct?

Just want to make sure...

 

[Flyer_PE]

In short, the answer is yes.  For a per-unit calculation, all of the impedance values have to be converted to a common base before calculating total system values.