Calculating base values

[anon6912]

When calculating base values for current, impedance etc
do we use the line to line voltage or the phase voltage?

What's the reason for using one over the other?

[0xDEADBEEF]

What is a "line to the line voltage"? What is "phase voltage"? I don't understand your question.

[Jiggy-Ninja]

My best guess is that he's asking about polyphase AC circuits, likely 3-phase.

I don't know much about 3-phase though.

[I_am_learning]

If you are talking about per-unit system, this is the usual practicce.
Take Total 3-phase power S, as base power,
Take Line-to-Line voltage V, as base Voltage V.
Take Line-Current I, as base Current
Take an Impedance Z, as base impedance

But since you can only select two Base quantities independently, If you say take S and V as the initial base quantities (which is the usual practice) then
I = S / sqrt(3)*V

Now, the Impedance Z is assumed to be that impedance Z, which when connected in Star fashion in a 3 phase line with line-to-line voltage *V* will result in line Current *I*.

So, I hope that now you can find the base impedance Z, from the base voltage V and base Power S.