Characterization of DC Current Sensors With AC Distortion for Railway
Applications
Abstract
To assess the reliability of dc energy measurement equipment on-board
trains, a setup was developed to characterize current transducers under
realistic operating conditions. The operating principle is based on a
current ratio measurement technique. The reference sensor is a
high-precision zero-flux current transducer in combination with a
broadband high-precision current shunt. The influence of ac distortion
on this reference sensor was found to be within a few parts in
106 using an initial version of the setup, in which ac
distortion was applied through a separate winding. A revised version of
the setup employs a programmable electronic load to apply dynamic
currents up to 600 A. The setup was used to characterize a 100 μohm
high-current shunt resistor. The effect of dissipative heating on the dc
transresistance error was around 0.03 %, with a settling time of about
half an hour. The short-term intrinsic current dependence was also
around 0.03 %. The effect of ac distortion was within a few parts in
106. The intrinsic current dependence and the onset of
the heating effect were also observed when exposing the sensor to a
dynamic current profile that was recorded during a trip between two
successive underground train stations on Metro de Madrid. These results
demonstrate that the setup described in this paper is very effective for
characterizing dc current sensors for practical railway applications.
Future work will concentrate on even more demanding current signals,
such as chopped signals, and on other types of sensors and measurement
systems.