A current transducer includes a current transformer in which the conductor carrying the current to be monitored constitutes the primary. The transformer secondary is wound on a toroidal core. The transformer is operated below its cut-off frequency such that the output from the secondary is proportional to the differential of the current in the primary. The secondary output is integrated by an integrator to provide a measure of current in the primary and the integrator is initialized at predetermined intervals. A current measuring device for an electric machine, for example a reluctance machine, includes at least one of the current transducers.