Compensating Algorithm for a Measurement CT Considering the Effects of the Hysteresis Characteristics

This paper proposes a compensating algorithm for the secondary current of the measurement current transformer (CT) that removes the effects of the hysteresis characteristic of the iron-core. The exciting current resulting from the hysteresis characteristics of the core causes an error between the primary current and the secondary current of the CT. The proposed algorithm decomposes the exciting current into the magnetizing current and the core loss current and each of them is estimated. The core loss current is obtained from the secondary current and the core loss resistance. The core flux linkage is calculated and then inserted into the flux-current curve to estimate the magnetizing current. The exciting current at every sampling interval is obtained by summing the core-loss and magnetizing currents and then added to the measured current to compensate the secondary current. The performance of the proposed algorithm is validated under various conditions using EMTP generated data. The test results of a iron-core type electronic CT were included. The results indicate that the proposed algorithm can improve the accuracy of the measurement CT significantly, and thus reduce the size and the cost of the CT.