Harmonic analysis of ferroresonance in single-phase transformers

Ferroresonance is a power quality problem that is characterized by distorted overvoltage and current waveforms. This paper reviews the ferroresonance problem associated with a circuit involving an unloaded transformer that is connected to a source through a capacitor, and solution methodologies. A common simplified method based on fundamental frequency is revisited while emphasizing the impact of harmonic components. Time-domain numerical simulations are conducted on a transformer using manufacturer data and the solutions are analyzed in terms of their harmonic content in an attempt to determine at what point the switching between the different ferroresonance modes takes place. The damping effect by transformer core loss is also emphasized.