[3][4] The term ferroresonance was apparently coined by French engineer Paul Boucherot in a 1920 paper, in which he analysed the phenomenon of two stable fundamental frequency operating points coexisting in a series circuit containing a resistor, nonlinear inductor and a capacitor.
[1][7] However, ferroresonance generally occurs when a transformer driving a system with primarily reactive (large imaginary part) impedance experiences perturbation to a single electrical phase.
[11] Following perturbation, the transformer oscillates in and out of the saturated and unsaturated modes of operation each cycle, such that the cycle-average inductance cancels out the power line impedance.
Ferroresonant circuits exhibit a highly distorted waveform, and voltage and current at transitions in and out of the saturated mode typically show discontinuities or first-order singularities.
If the remaining phases are not quickly interrupted and the phenomenon continues, overvoltage can lead to the breakdown of insulation in the connected components resulting in their failure.