What is the proper formula for 3 phase turns ratio?

[Js20981]

What is the turns ratio for a delta wye 138000/12470 XFMR. What is the proper formula? Thanks

[Kalbi_Rob]

What is the turns ratio for a delta wye 138000/12470 XFMR. What is the proper formula? Thanks

First step is to only use phase to ground voltages.
For Delta, Line-to-Line = Phase-to-Ground voltages.
For Wye, SQRT(3) * Line-to-Line = Phase-to-Ground voltages. Vp=12470/SQRT(3)=12470/1.732=7199.8V

TTR=138000V/7200V=~19.166

Math should be correct minus rounding errors.

[southbury]

as the previous post already explained
These questions are hard to answer.

Even NETA is vague on the exams.

Given 138,000 to 12470
They do not tell you the connections( I protested these questions)



138,000 probably a line to line voltage so you would assume a delta
12470 probably a wye voltage. 12470/square root 3=7199.56=7200

138,000/7200=19.1666