Camara Exam 1 #4

[brad9m]

I am confused about the solution to #4.

3 phase transformer, 3600kVA, Z = 7.5%, turns ratio=25, Vpri = 11kV. Assume line value is base value. Find Z actual on secondary.

The solution says Zbase = V base / (sqrt(3) * I base)

I don't think this is true for both wye and delta transformers and the problem doesn't state what kind of transformer it is. Am I missing something?

Thanks,

Brad

 

[DK PE]

It appears you are being successfully misled, maybe because there is a turns ratio listed and you "just must" do something with it .... The relationship you listed: Zbase = V base / (√3 * I base) is true regardless of delta/wye. For a large % of per-unit problems, you just need to worry about the ratio line voltages on each side of transformer and not get hung up on delta wye configuration.

 

[Ivory]

Yep, if it is not asking for an individual phase, just ignore the wye/delta conversion