Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 12/05/2008 08:54:34
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I was watching a program yesterday about the effects of a comet impacting the Earth. One of the effects they talked about was a series of massive EM pulses that would circle the Earth and knock out power grids and anything electrical.
Is there any way a Faraday cage could be made that would shield electrical equipment from such a pulse? Or even protect a whole building, such as a hospital, if it had its own power source?
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I feel that a Faraday cage would shield from the electrostatic effects but it would have no effect on the magnetic field unless it was superconducting which is not very practical.
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A Faraday cage will screen electric and electromagnetic (but not pure low-frequency magnetic) fields.
As I understand it, the main issue with power grids (also following solar storms) is that low frequency atmospheric magnetic fields induce huge DC currents in the long-distance pylon cabling, which causes DC currents in the transformers at each end, causing them to go into magnetic saturation and therefore they cannot convert power and instead short or dissipate it. You're best off deliberately breaking the circuits and cutting the power before the magnetic pulse arrives.
Modern building regulations (advisory now, to become compulsory in the UK in the autumn - applicable to commerical buildings at least) do impose certain "Faraday cage" requirements - primarily to protect modern computer and IT equipment in the event of nearby lightning strikes. I stumbled across this last year - I think your cage has to have "holes" no bigger than 5x5m. This will pass microwave/UHF (mobile phone signals) but will slightly attenutate VHF broadcasts (100MHz) and will heavily attentuate 10MHz and down.
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OK. Thanks, guys.
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It is obvious that the 'DC' current induced in a long power line by the magnetic field of a giant pulse presents a considerable technological challenge the first solution that comes to mind would be to interpose a capacitor in series with the line but it would have to be very large both to pass the 50/60 Hz power and to withstand the induced surge voltage.
In the medical field this isolation problem is solved by transmitting power by means of light in a fibre optic cable, I do not know if this is used to power the repeaters in submarine fibre optics data cables but if not they too would be subject to this problem.
I doubt if this could be extended to large scale power transmission and the only solution seems to be to reroute where possible.
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The power in light in fibres is insufficient to provide anything useful in this regard. Repeaters are powered conventionally with wires providing electrical power. But an advantage is the distance between repeaters is much higher.