The amount of inductance is dependent on the magnetic circuit, but the nonlinear characteristics of the magnetic properties make it so that the magnetic circuit changes when the operating point changes. The leakage inductance has all of the same properties, but it also has a flux path in non-magnetic regions, making it easily affected by the arrangement and geometry of the winding in addition to the core. This is why a magnetic field analysis using the finite element method (FEM) is necessary when evaluating these types of inductance.
This Application Note explains how to obtain self-inductance and leakage inductance for two types of secondary coiling in a transformer: uniform coiling and close coiling.
Evaluating Leakage Inductance
The flux linkage of the primary coil is evaluated as the flux leakage because the magnetic flux produced by the primary coil eliminates the flux linkage of the secondary coil. The variations of the flux leakage versus time can be evaluated from the voltage terminal of the primary circuit because they are induced voltage.