Analysis for the Ferroresonance on the Transformer by Overvoltage and Prevention Measures

Ferroresonance is a non-linear vibrational phenomenon that is generated by the electrical interaction of the inductance compon ent with the capacitor component of a certain capacitance as the device of the inductance component such as a transformer is saturated due to the degradation, the wavef orm distortion of current and voltage, and the oscillation of overcurrent and overvoltage in a system. Recently, ferroresonance was generated from the waveform distortion of current and voltage, or the overvoltage or undervoltage phenomenon caused by the nature of an electrical power system and design technology of the transformer in the three phase transformer system. Hence, in general, ferroresonance analyzed by converting to the LC equivalent circuit. However, in general, the aforementioned analytical method only applies to the resonance phenomenon that is generated by the interaction of the capacita nce of bussbar and grounding, and switching as the capacitor component with PT and the transformer as the inductance component in a system. Subsequently, the condition where ferroresonance was generated since overvoltage was supplied as line voltage to the phase voltage and thus the iron core is saturated due to the interconnection between grounded and ungrounded systems could not be analyzed when single phase PT was connected in a △/Y connection system. In this st udy, voltage swell in the confi guration of grounded circuit of a step-up transformer with the △-△ connection linked to PT for control power and the ferroresonance generated by overvoltage when the line voltage of the △-△ connection was connected to the phase voltage of the grounded Y-Y connection were analyzed using PSCAD / EMTDC through the failure case of the transformer caused by ferroresonance in the system with the △-△ /Y-Y connection, and subsequently, the preventive measure of ferroresonance was proposed.