From the International Electrotechnical Commission webstore:
“IEC/TR 61869-102:2014(E) provides technical information for understanding the undesirable phenomenon of ferroresonance oscillations in medium voltage and high voltage networks in connection with inductive voltage transformers. Ferroresonance can cause considerable damage to voltage transformers and other equipment. Ferroresonance oscillations may also occur with other non-linear inductive components.”
For more information, visit the IEC here.