Ever heard of Ferroresonance?

What is Ferroresonance?

Ferroresonance is a dangerous phenomnon that occurs in 15kV systems to 35kV. From what I have read, this phenomenon occurs when the system was initially charged, but part of the system is disconnected and is isolated from ground with a light load resistance.

In some sense it maintains an charge, but this charge is oscillating at a high duty cycle.

Problems of Ferroresonance?

Since ferreoresonance is an unstable high voltage system (Overvoltage), it should be avoided. Possible effects:

- Damage to Generators

- Surge Arrestor failures

- Arc flashes, especially during the removal of fuses in a 3 phase system

Potential Conditions that cause Ferroresonance in Systems:

- Light Load Resistance

- Isolated/ungrounded branch in circuit

- Parallel 3-Phase connections

- Delta transformers that are not grounded

How to Prevent Ferroresonance?

- Higher load resistance to dampen the effects of Ferroresonance

- Provide grounding in systems

- Use switch gear instead of fuses at the power distribution pole

References:

Wikipedia

Roger Dugan's "Examples of Ferroresonance"

Cadick Corp - Technical Bulletin

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