Calibrating Sensors to Measure Braking Chopper Currents in DC Traction Units

A large part of the energy involved in the braking stage of conventional DC railway traction units is dissipated in rheostat resistors, which is controlled by means of a braking chopper. A setup was developed to calibrate transducers used to measure the resulting high-current chopped DC current signals under conditions mimicking the real application. Preliminary results indicate that the reference transducer used in this setup can accurately measure chopped signals with magnitudes up to at least 250 A and pulse repetition rates up to 500 Hz with uncertainties better than 0.01 %.