Comments on: QOTW #33 – Communications infrastructure after a nuclear explosion

By: Polynomial

Polynomial — Mon, 27 Aug 2012 09:48:11 +0000

I'm not sure that a high demand would change the amount of damage done. The issue is that the EMP induces huge currents in electrical wires, especially long ones like power lines. These currents would fry substations and junction boxes. The critical factor is the density of transformers.

If you have a very densely populated area, with industrial units, you're likely to have a large number of domestic substations (2.4kV -> 230V) and a few larger industrial (33kV -> 400V) substations. The transformers in these substations act as giant inductors, creating a buffer. This allows the current to produce a huge magnetic field around the coils of the transformer, instead of inducing further erratic currents down the secondary lines. Even the lines themselves can store a reasonable amount of potential as a magnetic field. The smaller substations are still likely to catch fire, but they act as a temporary buffer to absorb and dissipate some of the energy as an EM field and heat respectively.

In a less dense grid, you've got nowhere for the current to go. It'll just fry the hell out of all your gear, because you can't store enough energy as an electromagnetic field in order to dissipate it over a few seconds.

The only time I could see load being a factor is in countries like India, where the power grid is horribly contrived, poorly designed and massively overloaded. In such a situation, everything is so poorly isolated that small shorts can knock out the power to a town, so an EMP is likely to devastate the grid.

By: scottpack

scottpack — Fri, 24 Aug 2012 15:35:38 +0000

Not only is the electrical grid fragile because of how it operates, but the North American grid is fragile simply because of bad design! Let's not forget the Great Northeast Outage of 2003 where more than 50 million customers were out of service in Canada and the United States. All due to a single instance of over-demand from a northern Ohio generating plant.

By: Piskvor

Piskvor — Fri, 24 Aug 2012 12:54:25 +0000

Although transoceanic fiber is not damaged by EMP, the optical cables contain built-in electrical repeaters, which are powered by high-voltage electricity - carried by copper wires inside the cable. The shielding provide by oceans should be sufficient for the usual depths, but the cables need to come ashore somewhere. (This is the cables' weakness in various other scenarios as well)