As the field weakens, the aurora oval is less concentrated. So why would this be a problem, unless more stronger solar events happens.?
I do not see why the transformers would burn out.
In the big blackouts, the protection relays have taken lines down prematurely.
The real problem for transformer is the (near)DC currents flowing during such event, If (capacitive)series compensation on lines are used, this prevents DC flowing to/from transformers. This would allow riding the transformers through the event without blackouts.
Done, or rather half done. I scanned the essay and posted it to: I screwed up somewhere and ended up with individual 11 individual pages instead of one big PDF. I'll fix it and make it searchable eventually. Meanwhile, all 11 pages are in the ZIP file at: Enjoy.
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Jeff Liebermann jeffl@cruzio.com
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I'm thinking that the geological substrata might have the effect of a return path, and that means a LOT of energy because of a planet-sized ground loop situation.
Transmission lines just have more heatsinking available than transformers.
The bundle of charged particles ejected from the sun may have been spread o ut over planetary dimensions when the hit the earth, but the ground loops i nvolved would have been more localised - still big, but most of the energy being dissipated would have been correspondingly well spread out.
Some sources claim that the normal ground currents are in the order of
100 kA and increase during the storms to order of 1 MA. This is a slowly varying DC current.
The soil is not a good conductor, so there are going to be some ground potential differences between different geographical areas. When some grounded man made structures, such as pipelines or power lines connect these geographical areas, part of this DC current will take the "shortcut" and flow through these low resistance metallic structures,
The DC current is particularly harmful to transformers due to core saturation and hence overheating.
There are several ways of avoiding this, the best would be installing series compensation stations in long lines. For instance in an AC link between Sweden and Finland there is one. They are officially used to optimize line throughput during normal conditions, but also disconnect any DC paths between countries. This should allow normal operation even _during_ a severe solar storm.
The second best is to disconnect the transformer (and hence consumers) during the worst storms. I have no idea what the protection relays were like in old systems, but modern protection relays are very versatile. The issue is how set the parameters correctly in a
relay manufacturers have tools for setting up a fleet of relays, so apparently they also have some simulation features built in.
I have to look it up again for the details, but apparently the problem is a modest dB/dt, but over a loop with a huge area formed by the HV transmission line and the earth as the return path. This tends to saturate transformers and cause them to fail.
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