A current sensor arrangement for measuring an effective primary current in a primary conductor having a magnetic core for magnetic coupling of the primary conductor to a secondary conductor and a controlled voltage source connected to the secondary conductor and configured to apply a voltage with adjustable polarity to the secondary conductor so that a secondary current passes through the secondary conductor. A measurement and control unit is coupled to the secondary conductor and configured to generate a measuring signal that represents the secondary current, to continuously detect the occurrence of magnetic saturation in the core, and to reverse the polarity of the voltage upon the detection thereof in order to reverse magnetization of the core. Furthermore, the measurement and control unit is configured to evaluate a spectrum of the measuring signal and determine a frequency of a current passing through the primary conductor based on the spectrum.