Investigation on ferroresonance mitigation for potential transformer using memristor emulator

Abstract

A transformer plays a vital role in AC as well as DC power systems. Ferroresonance is one of the switching overvoltages caused by nonlinear resonance between a distributed capacitance and core inductance of transformer. It is characterized by periodic as well as aperiodic low frequency oscillation with severe overvoltages of 2- 4 p.u. and overcurrents, which sustain for long duration unless required energy is supplied to meet the circuit losses. newlineFrequently, Instrument transformers of AC systems, converter transformers of DC systems and even power transformers of isolated systems subjected to ferroresonance failed to compensate losses. Failure reports of EHV and UHV substations infer that the damage of IVT and CVT could be a reason behind partial or total destruction of power network. Practically, ferroresonance is being mitigated by using a small linear resistive load in instrument transformers. A series of combination of nonlinear inductance and resistance is newlinesuggested to suppress both harmonics of ferroresonance. Memristor is supposed to be the fourth fundamental passive element in future which behaves as a nonlinear resistance with memory property. The main objective of the work is to investigate the memristor performance as a protection device against all modes of ferroresonance. A preliminary study has been done on ferroresonance mitigation of a low power transformer using OPAMP, JFET and CuSO4 based memristor emulators. The emulator circuit is designed and developed as a nonlinear load according to mitigation requirement of transformer. The Grounding Memristor Emulator (GME) is constructed with two AD844 ICs, one AD633 amplifier, two resistors and one capacitor. The OPAMP based memristor emulator damped the ferroresonance oscillations and recovered 82.05% of secondary voltage under mitigation. newline newline