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Resistance and Reactance of the Transformer

05/28/2025

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

R 1

and

R 2

. Corresponding reactances are

X 1

and

X 2

, 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: $I 2 R 2$
Secondary reactive drop: $I 2 X 2$
Primary resistive drop: $I 1 R 1$
Primary reactive drop: $I 1 X 1$

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 $I 1 = KI 2$ , the referenced drops become:
- Resistive: K²I₂R₁
- Reactive: K²I₂X₁

Therefore this will be the load voltage.

Topics

Basic Physics Articles

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