Modeling of Small Common-mode Choke for EFT Interference Suppression at Analog Input Port

In this paper, a full circuit model of small common-mode choke is presented for the analog signal input port of Capacitor Voltage Transformer(CVT) equipment, and its protection performance is analyzed under Electrical Fast Transient(EFT) disturbance signals generated by the isolation switch operation in the power system. Firstly, the broadband impedance characteristics among the terminals of the choke coil were measured, the corresponding RLC circuit parameters are extracted. According to the frequency characteristics of the magnetic permeability and the impedance measurement results of the small choke coil, power function is proposed to describe the frequency-dependent variable resistance and inductance. Finally, the proposed full circuit model of the small choke coil was used to evaluate its suppression of EFT disturbance.