Thanks OP for shedding some light on this topic. Doing a little more research I came across this info that I thought was interesting and will post below for others to read.
Geomagnetic Induced Currents (GIC) can cause transformers to be driven into half-cycle saturation where the core of the transformer is magnetically saturated on alternate half cycles. A few amperes are needed to disrupt transformer operation. A GIC level-induced voltage of 1 to 2 volts per kilometer and 5 amperes in neutral of the high-voltage windings is sufficient to drive grounded wye-connected distribution transformers into saturation in a second or less.[i] During geomagnetic storms, GIC currents as high as 184 amperes have been measured in the United States in the neutral leg of transformers.[f] The largest GIC measured thus far was 270 amperes during a geomagnetic storm in Southern Sweden on April 6, 2000.
“If transformer half-cycle saturation is allowed to continue, stray flux can enter the transformer structural tank member and current windings. Localized hot spots can develop quickly inside the transformer’s tank as temperatures rise hundreds of degrees within a few minutes.[k] Temperature spikes as high as 750°F have been measured. As transformers switch 60 times per second between saturated and unsaturated, the normal hum of a transformer becomes a raucous, cracking whine. Regions of opposed magnetism as big as a fist in the core steel plates crash about and vibrate 100-ton transformers, which are nearly the size of a small house. This punishment can go on for hours for the duration of the geomagnetic storm. GIC‑induced saturation can also cause excessive gas evolution within transformers. Besides outright failure, the evidence of distress is increased gas content in transformer oil, especially those gases generated by decomposition of cellulose, vibration of the transformer tank and core, and increased noise levels of the transformers (noise level increases of 80 dB have been observed).i GIC transformer damage is progressive in nature. Accumulated overheating damage results in shortening transformer winding insulation lifespan eventually leading to premature failure.
“In addition to problems in the transformer, half-cycle saturation causes the transformer to draw a large exciting current which has a fundamental frequency component that lags the supply voltage by 90 degrees and leads to the transformer becoming an unexpected inductive load on the system. This results in harmonic distortions and added loads due to reactive power or Volt-Ampere Reactive (VAR) demands. This results in both a reduction in the electrical system voltage and the overloading of long transmission tie-lines. In addition, harmonics can cause protective relays to operate improperly and shunt capacitor banks to overload. The conditions can lead to major power failures.”[b]
Thanks OP for shedding some light on this topic. Doing a little more research I came across this info that I thought was interesting and will post below for others to read.
Geomagnetic Induced Currents (GIC) can cause transformers to be driven into half-cycle saturation where the core of the transformer is magnetically saturated on alternate half cycles. A few amperes are needed to disrupt transformer operation. A GIC level-induced voltage of 1 to 2 volts per kilometer and 5 amperes in neutral of the high-voltage windings is sufficient to drive grounded wye-connected distribution transformers into saturation in a second or less.[i] During geomagnetic storms, GIC currents as high as 184 amperes have been measured in the United States in the neutral leg of transformers.[f] The largest GIC measured thus far was 270 amperes during a geomagnetic storm in Southern Sweden on April 6, 2000.
“If transformer half-cycle saturation is allowed to continue, stray flux can enter the transformer structural tank member and current windings. Localized hot spots can develop quickly inside the transformer’s tank as temperatures rise hundreds of degrees within a few minutes.[k] Temperature spikes as high as 750°F have been measured. As transformers switch 60 times per second between saturated and unsaturated, the normal hum of a transformer becomes a raucous, cracking whine. Regions of opposed magnetism as big as a fist in the core steel plates crash about and vibrate 100-ton transformers, which are nearly the size of a small house. This punishment can go on for hours for the duration of the geomagnetic storm. GIC‑induced saturation can also cause excessive gas evolution within transformers. Besides outright failure, the evidence of distress is increased gas content in transformer oil, especially those gases generated by decomposition of cellulose, vibration of the transformer tank and core, and increased noise levels of the transformers (noise level increases of 80 dB have been observed).i GIC transformer damage is progressive in nature. Accumulated overheating damage results in shortening transformer winding insulation lifespan eventually leading to premature failure.
“In addition to problems in the transformer, half-cycle saturation causes the transformer to draw a large exciting current which has a fundamental frequency component that lags the supply voltage by 90 degrees and leads to the transformer becoming an unexpected inductive load on the system. This results in harmonic distortions and added loads due to reactive power or Volt-Ampere Reactive (VAR) demands. This results in both a reduction in the electrical system voltage and the overloading of long transmission tie-lines. In addition, harmonics can cause protective relays to operate improperly and shunt capacitor banks to overload. The conditions can lead to major power failures.”[b]