To establish a single European railway area, the European Commission requires, by 2019, that energy billings shall be computed on the actual energy consumed. So, in near future, all trains shall be equipped with an energy measurement system, whose measurement accuracy should be assessed and periodically re-verified, as required by EN 50463-2. For this purpose, the voltage and current transducers play a crucial role as their accuracy could determine the performance level of entire measurement system. To obtain reliable results, the accuracy of transducers should be tested with waveforms as close to real working conditions as possible. To assess the metrological characteristic of DC voltage and current transducers under real operating conditions, this paper presents a calibration set up able to generate up 6 kV for DC voltage and up to 300 A for DC current. The system is able to generate standard tests but also complex and non-stationary test signals which go well beyond the standard characterization procedures. As an example of its usage, some preliminary results of characterization of commercial voltage and current transducers are presented.