Ferroresonance phenomenon occurs in electrical circuits which are consisting of magnetizing cores, such as in the transmission and distribution networks with transformers, electrical machines or reactors. Transformers often operate close to the knee point of the magnetizing curve under normal condition. Therefore any sudden change in voltage or current can change the operating point on the magnetizing curve and saturation may result. This phenomenon is reflected in the change of the equivalent nonlinear reactance of the transformer. Now, if the value of the saturated reactance reaches a value such that it causes resonance with the equivalent capacitance of the network, then an over current or over voltage may occur. Transformers, electrical motors, reactors and generators are examples of equipment having magnetizing cores. Ferroresonance may cause melting of the lamination of the transformer or electrical machine which eventually may lead to the failure of the equipment. This type of fault can create long time interruptions. Possible causes of ferroresonance are switching, faults especially single line to ground or double line to ground, lightning, and Ferranti effect. Although some techniques had been applied to mitigate ferroresonance on CVTs, methods to mitigate ferroresonance on power transformers are almost not studied or reported. This report initially introduces the ferroresonance phenomenon, its definition and circumstances where it occurs. The software used for the simulation is then introduced, whereby the modeling work of the components relevant to the present work is discussed. The simulation work then follows, where suitable circuits for ferroresonance simulation were identified, including those for the mitigation techniques, namely the UPFC and STATCOM. The circuits used to represent the network are introduced and the simulation results are presented and discussed. The UPFC in mode-1 and the STATCOM techniques of mitigation had been shown to successfully mitigate the ferroresonance.
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