They love to cite that 1859 storm and the proverbial telegraph cables bursting into flames. Telegraph used the actual Earth as the common signal return, meaning the intercept area for stray magnetic field was beyond huge, so it's easy to see how everything blew up.
How is a solar storm going to affect fiber optic cable? My interned is via kA band satellite, the total cable length is about 20 feet.
Trans-ocean fibre cables use repeaters which need power. It is that power supply circuitry that could be disrupted.
John
This sounds kind of nutty, a single wire in the center of the cable bundle supplies DC power???
" All repeaters in a cable are powered in series. Power feed equipment (PFE) is installed at the terminal stations on the land. These PFEs inject huge voltage into the line - 3,000, 4,000, and up to 10,000 volts - to power each repeater on the cable."
I'd be surprised if it could induce much current in that little bit of loop area, under a mile or so of 25 ohm*cm conducting medium.
Hmm. The skin depth for a frequency of 1/day (1.2E-5 Hz) turns out to be around 2.5 km, so a major fraction of the field would actually reach there.
Cheers
Phil Hobbs
Not unreasonable--putting each repeater on its own individual thousand-mile extension cord would take up a lot of valuable cross-section.
Cheers
Phil Hobbs
How much shielding would the ocean provide?
Joe Gwinn
Not a huge amount for a frequency of 1/24 hours, because at that frequency the skin depth is comparable to the depth of the ocean. More in the winter, less in the summer. Maybe a factor of 2 or 3--it'll be the high voltage and small loop area that does the heavy lifting then.
Cheers
Phil Hobbs
Probably wouldn't be a bad thing to be without internet for a few days to give the world a good dose of reality.
For a given field strength, the lower frequencies ought to be less damaging due to less dphi/dt and induced voltage. Also, in series with a several-kV constant current supply, the induced voltage in a fibre-optic-cable-repeater power supply might be not much problem. IIRC the main concern was long power lines where they ground the neutral of the 3-phase transformers at each end of the line, and ~DC causes the transformer cores to saturate. IIRC allowing the neutral tap of the transformer to float at one end of the line was the solution, but has some disadvantage (maybe lightning protection?). Perhaps someone else here knows better.
So no spam from Chinese vendors for a while? That isn't a problem for me.
Are they designed to fail gracefully like modern Xmas tree bulbs or does a single point failure in an optical amp take the entire cable down ?
The amplifiers are usually short lengths of erbium doped fibre with pump lasers coupled to them. Modern repeaters have multiple pump lasers per amplifier for redundancy. The pump levels can be remotely controlled to adjust the gain distribution along the cable. Each cable will have multiple fibres. If a whole repeater fails, the light will pass straight through the unpumped erbium doped fibre amplifiers and it would probably be possible to increase the gains of adjacent repeaters to compensate. However, the operating speed might be degraded. If the switch-mode converters in a particular repeater fail, there are sure to be voltage clamps that allow current to continue flowing through the repeater to keep all the other ones operating.
John
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