Study on Transient and Frequency Response of Current Transformer Using Jiles-Atherton Model

Under severe fault conditions the core of a current transformer can saturate and the transformer output current is then no longer linearly related to the measured current. Digital relays may then fail to command breakers to open, thereby leading to dangerous or destructive overcurrents. In this paper, a compensation technique is proposed that utilises the Jiles-Atherton model to reproduce the primary current from the measured secondary voltage (or current) during transients. The Jiles-Atherton model allows accurate representation of the nonlinear core characteristics including saturation and hysteresis effects, and these are effectively modelled by a core magnetising current, which when added to the measured current and reflected through to the primary, gives a representation of the primary fault current. Simulation results are used to demonstrate the proposed compensation algorithm under different fault conditions, mimicking the response of a real current transformer in experiment. Even under severe fault conditions the primary side current can be accurately duplicated. The Jiles-Atherton model adopted in this paper takes into account the phenomenon of complete reversibility of magnetization, which was not considered in earlier current transformer modelling.