Harmonic Study in Electromagnetic Voltage Transformers

Ferroresonance is a complex electrical phenomenon which may cause overvoltages and overcurrents in electrical power system disturbing the system reliability and continuous safe operating. The ability to predict or confirm ferroresonance depends primarily on the accuracy of the voltage transformer model used in the computer simulation. In this study, at first an overview of the subject in the literature is provided. Then, occurrence of ferroresonance and the resulting harmonics in a voltage transformer are simulated. The effect of iron core saturation characteristic on the occurrence of harmonic modes has been studied. The system under study has a voltage transformer rated 100VA, 275 kV. The nonlinear magnetization cure index of the autotransformer is chosen with q=7. The linear core loss of the transformer core is modeled with linear resistance. Harmonic modes in the proposed power system are analyzed using MATLAB software. The results show that harmonics are produced in the considered substation and causes great effect on voltage transformer failure.