<P> When magnetic fields move about in the vicinity of a conductor such as a wire, a geomagnetically induced current is produced in the conductor . This happens on a grand scale during geomagnetic storms (the same mechanism also influenced telephone and telegraph lines before fiber optics, see above) on all long transmission lines . Long transmission lines (many kilometers in length) are thus subject to damage by this effect . Notably, this chiefly includes operators in China, North America, and Australia, especially in modern high - voltage, low - resistance lines . The European grid consists mainly of shorter transmission circuits, which are less vulnerable to damage . </P> <P> The (nearly direct) currents induced in these lines from geomagnetic storms are harmful to electrical transmission equipment, especially transformers--inducing core saturation, constraining their performance (as well as tripping various safety devices), and causing coils and cores to heat up . In extreme cases, this heat can disable or destroy them, even inducing a chain reaction that can overload transformers . Most generators are connected to the grid via transformers, isolating them from the induced currents on the grid, making them much less susceptible to damage due to geomagnetically induced current . However, a transformer that is subjected to this will act as an unbalanced load to the generator, causing negative sequence current in the stator and consequently rotor heating . </P> <P> According to a study by Metatech corporation, a storm with a strength comparable to that of 1921 would destroy more than 300 transformers and leave over 130 million people without power in the United States, costing several trillion dollars . The Daily Mail even claims that a massive solar flare could knock out electric power for months, but these predictions are contradicted by a NERC report that concludes that a geomagnetic storm would cause temporary grid instability but no widespread destruction of high - voltage transformers . The report points out that the widely quoted Quebec grid collapse was not caused by overheating transformers but by the near - simultaneous tripping of seven relays . </P> <P> Besides the transformers being vulnerable to the effects of a geomagnetic storm, electricity companies can also be affected indirectly by the geomagnetic storm . For instance, internet service providers may go down during geomagnetic storms (and / or remain non-operational long after). Electricity companies may have equipment requiring a working internet connection to function, so during the period the internet service provider is down, the electricity too may not be distributed . </P>

How long can a solar flare knock out power
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