The electro magnetic energy conversion is given by Ampere's law and Faraday's law respectively:
In this equation is the magnetomotive force that is supplied to the connected magnetic circuit, is the magnetic flux through the associated branch of this magnetic circuit. The negative sign of the induced voltage is due to Lenz's law.
The static inductance is calculated from the flux linkage
and the current :
This quantity is calculated for information only.
is set to
if .