Magnetising inductance of a transformer

what is Magnetising inductance of a transformer?

That is the inductance required by the core to fully complete its hysteresis loop.

This question would have better been posted on the power electronics threads, instead of analog IC design.

When a current passes by the winding of a transformer, we can consider (this is the standard model of a transformer) that the total magnetic flux has two components:
a) The magnetising flux, that closes by the ferromagnetic core and is concatenated with the other winding
b) The leakage or disperse flux, that passes by the air and is not concatenated with the other winding
Each one of the fluxes gives rise to a component of inductance. In the "T" model of a transformer they are clearly distinguished.
Normally, magnetising inductance is much greater than leakage inductance, then:
Magnetising inductance can be measured in a winding with the other one opened.
Leakage inductance can be measured in a winding with the other one short-circuited.
Regards

Z