Understanding Ferroresonance in Power Systems – Risks, Simulation, and Mitigation

Introduction: Ferroresonance in Power Systems

Ferroresonance is a nonlinear electrical phenomenon that poses a significant risk in medium- and high-voltage power systems. Unlike typical transient events that dampen quickly, ferroresonance can lead to sustained overvoltages capable of damaging transformers, breakers, and other critical equipment

At Keentel Engineering, we help utilities and developers evaluate and mitigate ferroresonance risks using advanced simulation tools like PSCAD/EMTDC. This ensures compliance, system resilience, and asset protection.

What is Ferroresonance?

Ferroresonance occurs when the nonlinear inductance of a saturable transformer interacts with system capacitances (such as those from transmission lines, breaker grading capacitors, or stray equipment capacitance). When resonance conditions are met at the system’s operating frequency, the result can be large currents and voltages, far exceeding design limits

Unlike simple resonance, ferroresonance is complicated by transformer core saturation, making it highly nonlinear and difficult to predict.

Need a study? Request a PSCAD-based assessment today.

System Example

In the study presented, ferroresonance was triggered when one breaker in a three-phase system opened properly while two remained stuck. This created an LC loop, causing transformer saturation and runaway overvoltage conditions

• Without saturation modeled: The system showed normal switching waveforms.
• With saturation modeled: Voltages rose dramatically, up to 4 p.u. (per-unit), threatening insulation and equipment integrity (see simulation results on page 4 of the PDF).

Design it right the first time—talk to our substation engineers.

Why Ferroresonance Matters

• Equipment Damage – Prolonged overvoltages can lead to transformer failure.
• Safety Risks – Stuck breakers or switching anomalies can trigger dangerous fault conditions.
• Reliability Concerns – Grid operators must account for ferroresonance in planning and operations.

At Keentel Engineering, our simulation studies provide insights into:

• Transformer saturation behavior
• The effect of load changes on ferroresonance
• System damping contributions from losses and connected equipment
  

Mitigation Strategies

Some approaches we recommend include:

1. System Modeling & Simulation – Using PSCAD or EMT studies to predict conditions.
2. Load Management – Adjusting transformer loading to reduce resonance risk.
3. Damping Enhancements – Adding system losses or resistive paths.
4. Design Modifications – Proper breaker coordination, surge arresters, or grounding strategies.
   

Conclusion

Ferroresonance is rare—but when it occurs, the consequences are severe: sustained overvoltages, insulation breakdown, and avoidable outages. The only reliable defense is proactive engineering: model the exact network (including transformer saturation), test credible switching scenarios, and implement damping, protection, and coordination measures before energization.

Keentel Engineering applies PSCAD/EMTDC studies and utility-grade practices to identify trigger conditions, quantify risk (e.g., p.u. overvoltage envelopes), and deliver clear mitigation options with implementation steps and protection setting guidance. Our work helps owners meet NERC/IEEE expectations while protecting critical assets and project timelines.

Frequently Asked Questions –   Ferroresonance

IEEE PES TR 126 Design Support

Keentel Engineering Advantage: We bring decades of experience in power system studies, PSCAD simulations, and NERC/IEEE compliance. Our team ensures that ferroresonance risks are identified early in the design phase, saving utilities and developers from costly outages and equipment damage.