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As I understand it the overhead ground wire found on major transmission lines is placed there in the event of a lightning strike which prevents a surge in the phase conductors. My question is, could this ground wire also provide protection from atmospheric surge/induction caused by a major solar storm?

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EMP from solar winds aka Carrington effect happens every hundred years or less (due to solar cyclic wobble from planet alignment with Jupiter which gives rise to an 11 year cycle) and there are longer cycles too, recorded by the Mayans in their calendar.

Ground induction effect is inductive and suppresses low frequency more than surge pulses. That's why they use delta for transmission and Y for distribution as delta gives high CMRR.

But earth magnetic field variations can also induce large currents on transmission lines, so 2 of 3 phases are always physically rotated (swap positions) every km or so to balance this common mode(CM) ULF magnetic field on long transmission lines.

The raised ground wire does indeed deflect lightning strikes to arc gapped lines and earth grounding, butis not always sufficient.

side notes

So in Florida, recently, I asked an outdoor tour guide who was afraid to go outside in the open Coral Castle tour during a lightning storm, "how many times do you get power failures in the 2nd highest lightning strike zone on earth?" He said none. I said "look at those power poles. Do you see the UHF wire antenna sticking up on every pole? That's a sharp tungsten lightning rod to create a high E field gradient and reduce the breakdown voltage relative to parallel wires so they are more attracted to ESD discharge from lightning and reduces the chance of lightning arrestor surges on grid so power does not fail momentarily ( open -reclose )."

I have experienced corona on a poorly grounded cottage antenna inside from a swag lamp to metal rimmed table thru the floor board and the direct hit was a block away on trees. I just saw a 1m long blue corona between the swag lamp and the kitchen table. My point was the short tungsten pole tips were well grounded to redirect the surges to damp earth rather than disrupt the grid. So I felt more protected even with an umbrella standing in the rain since the surrounding power lines were protected. But I wouldn't stand under a tree or use the umbrella in an open field. The tour guide felt some ease of mind from my understanding as an E field expert and 200kVdc tester of power transformers and bushings. So he continued our personal tour in the rain.

You will also note a large array of lightning rods above any TFMR substation to protect it and sometimes with overhead array ground wires to protect them .

EMP pulses cover an almost infinite spectrum from DC to gamma waves. Solar winds act as a current source of modulated flux of charges. Aurora is the discharge in the upper atmosphere near the poles which attempt to act as lightning rods and Plasma Physicists that I have worked with at the Churchill rocket research station have studied this since the late 70's using our Black Brandt research rockets and their electronics to detect the plasma field and transfer function (f) of the upper ionosphere in atmosphère up to ~500 miles above the earth, where there are geosatellites.

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