EXPERIMENTAL VALIDATION OF A SIMPLIFIED MODEL OF A CURRENT TRANSFORMER

Abstract

Modeling of current transformers (CTs) is essential for assessing their transient performance, as the nonlinear magnetizing characteristic of the iron core can lead to severe secondary current waveform distortion. Such effects are particularly critical for the measurement accuracy of protection relays, whose reliable and fast operation depends on the faithful reproduction of the secondary current. This paper presents the experimental validation of a simplified dynamic CT model that includes only the nonlinear (anhysteretic) magnetizing characteristic, while neglecting the winding resistance and leakage inductance. The magnetizing characteristic was measured using a commercial CT analyzer. To align the measured and simulated secondary currents, an optimization procedure was used to determine the initial value of the remanent magnetic flux. The optimization was applied to a transient condition, in which a primary current contains an aperiodic component, typical for power system faults. The simulated secondary current was then compared to the measured current using the range-normalized Root-Mean Square Error (NRMSE) method. After optimization, an NRMSE value ranging from 2% to 5% was achieved for the CT under consideration across six validation scenarios.