The relationship between percent and per unit impedance

[Callum Plunkett]

Homework Statement

For one of my assignments I’ve been ask about the relationship between percent impedance and per unit impedance.

Homework Equations

The Attempt at a Solution

I know that the x% is determined in transformers by short circuiting the secondary windings and slowly increasing the voltage until the secondary gives the desired full load current. And that x p.u is the x % converted into number form which has the advantage of simplifying calculations on more complex circuits. But other than that I’m unsure if there is anything else I can add to my answer. Can anyone point me in the right direction?

 

[anorlunda]

If you were doing a study of the national power grid, how would you choose a per unit base for the study?