Z base should be the same if u used 3phase equation or single phase equation it is 0.023. Zb=V^2 / S (single phase) x sqrt3=270*270(V^2 )/3333333 S (single phase)=0.023
also
Cram for the Professional Engineer Electrical and Computer Power Exam by James Flanagan (some writing and circled answers) $15
Cram for the Professional Engineer Electrical and Computer Power Exam Sample Test Volume I by James Flanagan (some writing and circled answers) $15
Cram for...
i'm interested in
The Electrical Engineer's Guide to Passing the Power PE Exam by Alexander S. Graffeo (Writing throughout and blank sheets at the end are completely filled with formulas and notes) $30