- Leakage Reactance Definition: Leakage reactance in a transformer is defined as the self-reactance caused by leakage flux that links either the primary or secondary winding but not both.
- Transformer Impedance: Impedance of a transformer is the combination of its resistance and leakage reactance, affecting voltage drops in windings.
- Resistance in Windings: The primary and secondary windings of a transformer, made of copper, possess inherent resistance.
- Voltage Drops: Voltage drops in transformer windings are due to their impedance, which includes resistance and leakage reactance.
- Leakage Flux Path: Leakage flux in a transformer passes through the winding insulation and transformer oil, leading to leakage reactance.
Leakage Reactance of Transformer
In a transformer, not all the flux links both windings. Flux that links only one winding is leakage flux. That leakage flux produces self-reactance in the winding it links.
That self-reactance is also called leakage reactance. Together with the transformer’s resistance, it is impedance. This impedance causes voltage drops in the primary and secondary windings.
Resistance of Transformer
The primary and secondary windings of an electrical power transformer are usually copper. Copper is a good conductor of current but not a superconductor, and superconductors are not in ordinary use. So the windings have resistance, taken together as the transformer’s resistance.
Impedance of Transformer
Both windings therefore have resistance and leakage reactance. That pair is the impedance of transformer. If R1 and R2 and X1 and X2 are the primary and secondary resistance and leakage reactance of transformer, the winding impedances Z1 and Z2 are
Transformer impedance also governs parallel operation of transformer.
Leakage Flux in Transformer
In an ideal transformer every flux line would link both windings. In a real machine it does not. Most flux stays in the core of transformer, but some links only one winding. That remainder is leakage flux. It travels through the winding insulation and transformer oil instead of the core. Leakage flux produces leakage reactance in both windings: magnetic leakage.
Winding voltage drops come from the impedance of transformer. Impedance is resistance plus leakage reactance. Apply voltage V1 to the primary and a term I1X1 balances the primary self-induced EMF from leakage reactance (X1 is that leakage reactance). Add the primary resistance drop and the transformer voltage equation is
The secondary side with leakage reactance is
The figure draws the primary and secondary on separate limbs. That layout leaves a large space for leakage flux. Leakage would vanish if both windings occupied the same space. That is not possible, but putting secondary and primary concentric cuts leakage a long way.
