Electrical transformer with unidirectional flux compensation, with the following features: a) the transformer has a soft-magnetic core on which, in addition to a primary and secondary winding arrangement (1, 2), a compensation winding arrangement is arranged, b) a magnetic field measuring device measures a flux interlinked with a current in the primary or secondary winding arrangement and provides a control signal (14, 15), c) the control signal (14, 15) is fed to a current control device (12, 13), d) the current control device (12, 13) is connected to the compensation winding arrangement via a current path that contains a reactance dipole and the current control device (12, 13) in accordance with a control signal (14, 15) feeds into said compensation winding arrangement a compensation current (16, 17) in such a way that the effect of said compensation current in the core is in a direction opposite to a magnetic unidirectional flux. e) the magnetic field measuring device is formed from a signal processing unit that is connected in a signal-conducting manner to at least two magnetic field detectors, f) the signal processing unit is set up for ascertaining overtones from in each case one measurement signal provided by the magnetic field detector in order to ascertain from said overtones the control signal (14, 15) for correctively adjusting the unidirectional flux, g) the control signal (14, 15) is formed from the first overtone (second harmonic), h) the core has three limbs (21, 22, 23), at least two of which (21, 23) in particular are fitted with a compensation winding, characterised in that i) the magnetic field measuring device measures the stray magnetic field that closes outside the core via the air path in order to provide the control signal, j) each of the at least two magnetic field detectors is arranged outside the core for registering a stray flux of the transformer, k) each magnetic field detector is embodied as an induction probe. l) each induction probe is an air-cored coil, m) each air-cored coil is arranged in a gap, formed from an outer circumferential surface and an enclosing compensation winding or a winding, approximately at centre limb height. a) the transformer has a soft-magnetic core on which, in addition to a primary and secondary winding arrangement (1, 2), a compensation winding arrangement is arranged, b) a magnetic field measuring device measures a flux interlinked with a current in the primary or secondary winding arrangement and provides a control signal (14, 15), c) the control signal (14, 15) is fed to a current control device (12, 13), d) the current control device (12, 13) is connected to the compensation winding arrangement via a current path that contains a reactance dipole and the current control device (12, 13) in accordance with a control signal (14, 15) feeds into said compensation winding arrangement a compensation current (16, 17) in such a way that the effect of said compensation current in the core is in a direction opposite to a magnetic unidirectional flux. e) the magnetic field measuring device is formed from a signal processing unit that is connected in a signal-conducting manner to at least two magnetic field detectors, f) the signal processing unit is set up for ascertaining overtones from in each case one measurement signal provided by the magnetic field detector in order to ascertain from said overtones the control signal (14, 15) for correctively adjusting the unidirectional flux, g) the control signal (14, 15) is formed from the first overtone (second harmonic), h) the core has three limbs (21, 22, 23), at least two of which (21, 23) in particular are fitted with a compensation winding, characterised in that i) the magnetic field measuring device measures the stray magnetic field that closes outside the core via the air path in order to provide the control signal, j) each of the at least two magnetic field detectors is arranged outside the core for registering a stray flux of the transformer, k) each magnetic field detector is embodied as an induction probe. l) each induction probe is an air-cored coil, m) each air-cored coil is arranged in a gap, formed from an outer circumferential surface and an enclosing compensation winding or a winding, approximately at centre limb height.