Turn Ratio

(also turns ratio), the ratio of the electromotive forces (emf’s) induced in the primary and secondary windings of a transformer by the mutual magnetic flux, that is, the flux in the magnetic circuit. It is equal to

where e₁ and e₂ are the emf’s in the primary and secondary transformer windings, w₁ and w₂ are the numbers of turns in the primary and secondary windings, and Φ is the mutual magnetic flux. In practice the turn ratio is defined as the ratio of the rated supply voltage of the primary winding to the voltage of the open secondary winding, and the error caused by the difference between the emf and the voltage of the primary winding is neglected.