Leakage Inductance

Definition

Leakage inductance in a transformer is an inductive component that results from the imperfect magnetic linking of one winding to another.

In an ideal transformer, 100% of the energy is magnetically coupled from the primary to the secondary windings. Imperfect coupling reduces the signal induced in the secondary windings. The electrical equivalent is some self-inductance in series with the primary windings that are properly coupled. This series inductance is the "leakage inductance."