leakage inductance

The leakage inductance expresses the missing coupling part, which does not contribute to the energy transfer in case of a magnetic coupling of two inductors.

In an ideal coupling of two inductors, one hundred percent of the energy is transferred from one coil to the other. Since such an ideal inductive coupling cannot be realized, in practice stray losses occur, which are expressed in a low degree of coupling and which result in signals from the primary winding being induced into the secondary coil with reduced energy. The reason for this is that part of the magnetic coupling field is not coupled into the second inductor as leakage flux.