Why is ferroresonance a concern in distribution systems, and what mitigation techniques can be employed?

Ferroresonance is a nonlinear resonance phenomenon that can occur in power systems when a capacitive reactance is connected in series with a nonlinear inductive reactance, typically the magnetizing inductance of a transformer. It's a concern because it can lead to overvoltages, overcurrents, and harmonic distortion, potentially damaging equipment and disrupting service. Ferroresonance is often triggered by switching operations, such as energizing an unloaded transformer or opening a single phase of a three-phase circuit. The overvoltages caused by ferroresonance can exceed the insulation withstand levels of equipment, leading to flashovers and insulation failure. The overcurrents can damage transformers and other equipment. The harmonic distortion can interfere with the operation of sensitive electronic devices. Several mitigation techniques can be employed. Adding a damping resistor in series with the capacitor can reduce the magnitude of the resonant oscillations. Using three-phase transformers instead of single-phase transformers can reduce the likelihood of ferroresonance. Avoiding single-pole switching of three-phase circuits can also help. Applying surge arresters can protect equipment from overvoltages. Implementing proper switching procedures can minimize the risk of triggering ferroresonance. Using transformers with a lower saturation level can also help to reduce the severity of ferroresonance. Careful system design and operating practices are essential to prevent ferroresonance in distribution systems.