Ferroresonance Effects

Ferroresonance is a mysterious phenomenon that seems to occur capriciously, causing much concern among utility operating personnel. It generally occurs during a system imbalance, usually during switching, that places capacitance in series with transformer magnetizing impedance. This can result in high overvoltages that can cause failures in transformers, cables, and arresters. Any system capacitance can be involved in ferroresonance, but the major concern is about underground cable capacitance.


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  • Discusses the phenomenon of ferroresonance, which causes concern among utility operating personnel.
  • Explains ferroresonance and why it does not occur at 12 kV.
  • Presents the two main circuit configurations that cause ferroresonance.
  • Describes the symptoms of ferroresonance.
  • Discusses ferroresonance and underground cable capacitance.