Calibration of Voltage and Current Transducers for DC Railway Systems

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 the near future, all the trains shall be equipped with an energy measurement system, whose measurement accuracy should be assessed and periodically reverified, as required by EN 50463-2. As for every energy and power measuring system, the voltage and current transducers play a crucial role as their accuracy could determine the performance level of the entire measurement chain. To answer to this emerging need, this paper presents a calibration system allowing the accurate testing of dc voltage and current transducers, up to 6 kV and 300 A and up to 10 kHz. It is able to reproduce all the tests prescribed by EN 50463-2, but in order to characterize the transducers in actual operating conditions, a series of additional tests can also be performed using synthetic complex waveforms or even signals acquired on-board trains. The expanded uncertainty (level of confidence 95%) of the calibration system is 43 μV/V and 24 μA/A at dc and 520 μV/V and 820 μA/A at 10 kHz. Moreover, the calibration of two commercial voltage and current transducers, currently installed in the trains of an Italian operator, is presented.