After some searching I found this PDF presentation: "Geomagnetic Storms
and the US Power Grid" https://www.swpc.noaa.gov/sites/default/files/images/u33/fin... , which says: "GIC are Quasi DC currents" and "Moderate Storm - Electric Field at Earth’s Surface 1-5 V/km / Largest recorded 20 V/km" and
Let's assume 10x worse than largest recorded, 200 V / km.. not sure if this is physically possible but probably a worst case.
A high-voltage transmission lines would be in danger, as presentation said. Not only because of overvoltage, but also because this is injecting DC into lines designed for AC only.
A 10 km old-style telephone or telegraph line would get 2000 volt on it... this would definitely burn the equipment or set it on fire.
What about my house? The AC comes in from nearest distribution transformer ("pole pig"). The nominal output is 110V RMS (155V peak), and let's say there is ~0.6 miles (1 km) from it to my house. This will be 355V peak arriving, equivalent to 251V RMS. My appliances and lights (which were turned on) are likely gone... but many computers might survive, as modern power supplies are often rated "90-240V" for european usage (and they don't care about AC/DC mix either). And of course if you had any surge protectors in your extension cords, they'd protect your devices -- they were designed exactly for situations like those.
What about my local network? There are less then 100 meters of distance, so 20V induced voltage.. and common Ethernet is rated for 2000V, so this is going to be fine.
What about USB cords, low-voltage power cords, etc...? Well, those are shielded / have two wires right next to each other, so they would normally be unaffected. But let's say you had a bad ground connector or incompletely plugged in device, so you have a loop. In this case, 2 meter (6ft) cable would have 0.4 volts. That's within tolerances of most ICs, they'd be fine.
What about unplugged device? Your 18" laptop will develop 0.08 volts in the worst case. Most of the modern ICs run in 0-1V range, so they won't burn up (but might have some glitches if device is working). Your antennas (WIFI and 3G) would also develop extremely low voltage so they would be fine as well.
TL/DR: country-wide systems (power grid, old telegraph) is in trouble. City-wide might or might not survive. Anything smaller than a house is fine. If you are worried about second Carrington, get water, food and generator, and get some surge protectors.
Voltage is only half the story with electrical equipment. Pretty much anything you buy is designed to withstand voltages far in excess of nominal. Almost every input on an electronic device will have "transient voltage supression" ESD protection diodes which will short high voltages to ground. This is generally because of static electricity. The potential difference between a person and ground can easily reach 5kV. Generally any device you buy today will have been tested to some sort of ESD standard - often to 8kV discharge voltage.
Other tests done during electromagnetic compatibility testing (EMC) include bombarding things with radio waves, testing susceptibility to surge voltages and injecting voltages into power cables.
The key for all of these is duration and total energy. A TVS diode can deal with high voltages - but if they're sustained for too long the diode will burn up. The testing regimes all use quite low total energies.
The values you give for geomagnetically induced currents talk about volts per km. EMC testing of industrial equipment is typically done at volts per meter - a factor of 1000x greater. The industrial standards require 10 V/m, military stuff is tested at 200 V/m.
Right, and from my reading there is no strong EMC components in the solar storms. Radios are disrupted, but from ionosphere changes, not from jamming. it is mostly the weird GIE thing which is described as "quasi-DC", and also mentions "millions of amperes"
So all that EMC stuff is very important in everyday life (and it killed more than one FET :) ), but seems inapplicable for Carrington-style event. There, it will be all about huge currents and low voltages. If the wire is long enough, TVSs may burn out, capacitors may overvolt and explode, any ESD protection diodes will also get destroyed. Luckily, we don't have a lot of long-distance copper wires connected to sensitive electronics.
I am not an expert on long-distance transmission lines, but according to that presentation the failures are not caused by instantaneous overvoltage / arc-over (microseconds), but rather by DC imbalance and overheating (seconds to minutes). Which means a better protection technology can fix it, turning permanent equipment damage into temporary shutdowns.
The latest example is 1989 Quebec power blackout: https://en.wikipedia.org/wiki/March_1989_geomagnetic_storm . The storm tripped some protections, that overloaded other circuits which tripped as well, and the whole province went dark. It took 90 seconds for everything to shut down, and 9 hours to restore everything. Judging by that timeline, no major equipment was damaged.
I keep reading about government mandating solar storm protection for power grids.. hopefully next time a big storm comes, we'll be more protected than Quebec in 1989.
Apparently the electrical fires were from GIE (https://en.wikipedia.org/wiki/Geomagnetically_induced_curren... ), which are "measured in V/km".. but how big were they?
After some searching I found this PDF presentation: "Geomagnetic Storms and the US Power Grid" https://www.swpc.noaa.gov/sites/default/files/images/u33/fin... , which says: "GIC are Quasi DC currents" and "Moderate Storm - Electric Field at Earth’s Surface 1-5 V/km / Largest recorded 20 V/km" and
Let's assume 10x worse than largest recorded, 200 V / km.. not sure if this is physically possible but probably a worst case.
A high-voltage transmission lines would be in danger, as presentation said. Not only because of overvoltage, but also because this is injecting DC into lines designed for AC only.
A 10 km old-style telephone or telegraph line would get 2000 volt on it... this would definitely burn the equipment or set it on fire.
What about my house? The AC comes in from nearest distribution transformer ("pole pig"). The nominal output is 110V RMS (155V peak), and let's say there is ~0.6 miles (1 km) from it to my house. This will be 355V peak arriving, equivalent to 251V RMS. My appliances and lights (which were turned on) are likely gone... but many computers might survive, as modern power supplies are often rated "90-240V" for european usage (and they don't care about AC/DC mix either). And of course if you had any surge protectors in your extension cords, they'd protect your devices -- they were designed exactly for situations like those.
What about my local network? There are less then 100 meters of distance, so 20V induced voltage.. and common Ethernet is rated for 2000V, so this is going to be fine.
What about USB cords, low-voltage power cords, etc...? Well, those are shielded / have two wires right next to each other, so they would normally be unaffected. But let's say you had a bad ground connector or incompletely plugged in device, so you have a loop. In this case, 2 meter (6ft) cable would have 0.4 volts. That's within tolerances of most ICs, they'd be fine.
What about unplugged device? Your 18" laptop will develop 0.08 volts in the worst case. Most of the modern ICs run in 0-1V range, so they won't burn up (but might have some glitches if device is working). Your antennas (WIFI and 3G) would also develop extremely low voltage so they would be fine as well.
TL/DR: country-wide systems (power grid, old telegraph) is in trouble. City-wide might or might not survive. Anything smaller than a house is fine. If you are worried about second Carrington, get water, food and generator, and get some surge protectors.