What caused the failure of the Canadian power plant in March 1989?
On March 23, 1989, Hydro-Quebec had a 9 hour blackout affecting 9 million people. The cause was a geomagnetic induced current (GIC) due to a large geomagnetic storm. GICs can put some transformers into what is known as half-cycle saturation, where the current in the windings can exceed the rated load for the device, and magnetic flux which is normally constrained to the transformer core can leak into adjacent structures. This can result in heating and damage to the device and adjacent structures. Note that the dramatic complete failure of a transformer does not occur very often. However, there is evidence that the lifetime of transformers in GIC susceptible regions is shorter than the lifetime of transformers in non-GIC susceptible regions. This suggests that GIC more commonly affects transformers by small amounts over time. In addition to problems in the transformer itself, half-cycle saturation causes the transformer to draw a large exciting current which has a fundamental frequency
