What Is Ferroresonance in a Transformer?
Quick answer — Ferroresonance is a non-linear resonance between a transformer (or its magnetising inductance) and the network capacitance (typically cable capacitance), which can produce sustained overvoltages and overcurrents far above normal. It is caused by the saturation of the transformer core and occurs under certain system configurations, energising sequences, or faults — and can damage the transformer, arresters and other equipment.
Contents
What is ferroresonance and why is it dangerous?
How it occurs
A series or parallel resonance forms between the transformer (non-linear inductance) and the line/cable capacitance. Under certain conditions — e.g. a cable with a transformer open or a particular breaker sequence — the voltage is not limited by linear analysis and can jump.
Symptoms
Severe, sometimes chaotic overvoltages and overcurrents, audible noise, and possible excessive currents that overheat the transformer or damage arresters.
Prevention
Avoid unfavourable configurations, use proper switching sequences, consider resistive loading, surge arresters and, where needed, a ferroresonance study.
References & standards
- IEC 60076-1
- IEEE C57.12.00
Related
Related manufacturers
Acme Electric (Hubbell) · Central Moloney · CORE Transformers · Daelim Transformer (US) · Delta Star · Eaton
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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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