Ferroresonance — Transformer Glossary

A nonlinear resonance phenomenon involving the interaction between a transformer's magnetizing inductance and system capacitance, causing dangerous overvoltages.

Backelectrical

Ferroresonance

A nonlinear resonance phenomenon involving the interaction between a transformer's magnetizing inductance and system capacitance, causing dangerous overvoltages.

Ferroresonance can produce sustained overvoltages of 2–4 times nominal, damaging insulation and connected equipment. It typically occurs in ungrounded or resistance-grounded systems when one or two phases are disconnected (e.g., blown fuse, single-phase switching). Prevention includes: using grounded-wye connections, adding damping resistors, and avoiding single-phase switching of transformers with long cable connections.

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Inrush CurrentThe transient surge of magnetizing current that flows when a transformer is first energized. Can reach 8–12 times the rated full-load current.

Core SaturationThe condition where the core's magnetic flux density reaches a level where further increases in magnetizing current produce diminishing increases in flux.