Process for the operation of a transformer connected to a controllable voltage source as well as an apparatus for the implementation of that process

The method involves disconnecting a voltage source (2) from a transformer (1) when an output current (iA) exceeds a maximum permissible value. An output voltage (uA) is formed in response to a start signal (Ss), as a function of a transformer voltage that is determined recently before the output current exceeds the permissible value and as a function of magnetic fluxes (phi1, phi2). An Independent claim is also included for an apparatus for carrying out a method of operating a transformer from a drivable voltage source.