Note on the Measurement of Transformer Turns-Ratio

This note shows that in many important cases the turns-ratio of iron-core transformers is given by the simple relation N
1
/N
2
= √X
sc1
/X
sc2
, in which X
sc1
and X
sc2
are the reactive components of the short-circuit primary and secondary impedance of the windings concerned. The measurements are conveniently made with an impedance or inductance bridge. This equation also gives the turns-ratio of certain air-core transformers.