Ferroresonance in Power and Instrument Transformers

This chapter describes the fundamental concepts of ferroresonance phenomenon and analyzes its symptoms and the consequences in transformers and power systems. Due to its nonlinear nature, the ferroresonance phenomenon can result in multiple oscillating modes which can be characterized based on the concepts of the nonlinear dynamic systems, e.g., Poincare map. Among numerous system configurations which can experience the phenomena, a few typical systems scenarios, which cover the majority of the observed ferroresonance incidents in power systems, are introduced. This chapter also classifies the ferroresonance study methods into the analytical and the time-domain simulation approaches. A set of analytical approaches are presented, and the corresponding fundamentals, assumptions, and limitations are discussed. Furthermore, key parameters for accurate digital time-domain simulation of the ferroresonance phenomenon are introduced, and the impact of transformer models and the iron core representations on the ferroresonance behavior of transformers is investigated. The chapter also presents some of the ferroresonance mitigation approaches in power and instrument transformers.