Mitigation of ferroresonance in power system

Abstract

The onset of a ferroresonance phenomenon in power systems is commonly caused by the reconfiguration of a circuit into the one consisting of capacitances in series and interacting with transformers. The reconfiguration can be due to switching operations of de-energisation or the occurrence of a fault. Sustained ferroresonance without immediate mitigation measures can cause the transformers to stay in a state of saturation leading to excessive flux migrating to transformer tanks via internal accessories. The symptom of such an event can be unwanted humming noises being generated but the real threatening implication is the possible overheating which can result in premature ageing and failures. The main objective of this project is to determine the accurate models for transformers, transmission lines, circuit breakers and cables under transient studies, particularly for ferroresonance. The second objective is to find out methods to mitigate these phenomena. All simulation studies are carried out using an electromagnetic transient program, called ATP Draw. Simulation studies revealed that the key circuit parameter to initiate transformer ferroresonance in a transmission system is the circuit-to-circuit capacitance of a double-circuit overhead line. The extensive simulation studies also suggested that the ferroresonance phenomena are far more complex and sensitive to the minor changes of system parameters and circuit breaker operations. Adding with the non-linearity of transformer core characteristics, repeatability is not always guaranteed for simulation and experimental studies