Eli5 how could an electromagnetic impulse, say from the sun for example, disable a whole power grid?
In: Physics
Top response is incorrect.
The issue for transmission is not the directly induced current from the radiation to the line. That’s only an issue for small PCBs with undersized traces, but even then it’s the secondary concern. The issue is that the rapid changes in the earth’s magnetic field will induce a voltage in the ground itself across several miles and can last several minutes or longer. This isn’t high enough to be problematic for humans, but if you have equipment that depends on having a common reference point (literally “ground”) and they suddenly don’t, then you can have what are called Ground Induced Currents, which will take the path of lowest resistance, which means it will go from the ground into the equipment and into the system, which is literally designed to have as low a resistance as possible to save energy and money (resistance means heat, and heat is energy bought that is not sold.) Transmission lines aren’t usually (edit: earth) grounded (look up delta vs wye if you want) and can handle this increased current with more or less no issues. Transformers are the real problem because of what’s called core saturation.
Transformers work by magnetic Flux in = magnetic Flux out. Magnetic Flux is based on the product of the number of turns, voltage, and current on each side. If you are running your transformers at 80 or 90% of nominal and suddenly increase the current on one side, you’ll leave what’s called the “linear region” of behavior and enter the “saturation region” (read: non-linear) and the core will heat up very quickly, which is bad. Transformers monitor their temperature and if it gets too hot, they’ll force out of service to stop damage. Lines do this too, but like I said, they’re not grounded, and their temperature curves are more generous.
If multiple transformers do this at once, or if another disturbance happens at the same time, it can lead to what’s called a “cascading condition” which is the thing you see in movies where its multiple events bang bang bang bang, cities blacking out one block at a time, switches operating one after another, all trying to protect themselves (overload trips itself, which causes another overload, which trips to protect itself which causes another overload.) If the operators don’t pre-posture their system for that eventuality before it starts and the system isn’t designed to handle the transient behavior, then that cascading condition can black out either the entire system or a large part of it. Check out the 2003 northeast blackout to see what cascading looks like. I believe California had one as well in 2008 ish.
Source: monitoring GICs are in my job description. If you wanna look up more stuff, the NERC term for this event is a Geomagnetic Disturbance (GMD)
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