To provide a method and an apparatus for operating a transformer from a drivable power source.

The method for operating the transformer from the drivable power source comprises the steps of generating an output voltage (uA) to supply a valid power and/or a reactive component from a power (2) to an AC voltage supply network (3) through a transformer (1), monitoring an output current (iA) from the power source (2) with respect to a maximum allowed value (iAmax), in this case the magnetic flux (Φ) of the transformer (1) is determined continuously, and disconnecting the power source (2) from the transformer (1) when the current (iA) exceeds the value (iAmax).