Resistance and Reactance of the Transformer

Transformer Resistance and Reactance Representation
Resistance Definition

The resistance of a transformer refers to the internal resistance of its primary and secondary windings, denoted as R₁ and R₂. Corresponding reactances are X₁ and X₂, with K representing the transformation ratio. To simplify calculations, impedances can be referred to either winding—either primary terms referred to the secondary side or vice versa.

Voltage Drops in Windings

Resistive and reactive voltage drops in primary and secondary windings are:

• Secondary resistive drop: I₂R₂

• Secondary reactive drop: I₂X₂

• Primary resistive drop: I₁R₁

• Primary reactive drop: I₁X₁

Primary-to-Secondary Referencing

When referring primary drops to the secondary side using transformation ratio K:

• Primary resistive/reactive drops become K⋅I₁R₁ and K⋅I₁X.

• Substituting I₁ = KI₂, the referenced drops become:

• Resistive: K²I₂R₁

• Reactive: K²I₂X₁

Therefore this will be the load voltage.