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Understanding the Electromagnetic Pulse (EMP)

In the near future article, I will be discussing ways to mitigate damage from an EMP event using hardened solutions needed to keep mission-critical systems operational.

I recently came across an article entitled “Effect of the FAST NUCLEAR ELECTROMAGNETIC PULSE on the Electric Power Grid Nationwide: A Different View”, by Mario Rabinowitz from the Palo Alto, CA Electric Power Research Institute. It is an older article (circa 1987), but I believe that the essence of the report gives a feel for EMPs vs. Lightning strikes. It essentially says that the EMP is no more damaging than to the power grid than a lightning strike.

Here is what Rabinowitz says:

Of the two basic kinds of EMP, one is a relatively slow electro-magnetic pulse called magnetohydrodynamic EMP(MHD EMP), lasting < about 102 sec., E < about 10-1 V/m. This is similar to solar storms which last approximately 10 min, E > about 10-2 V/m. The other gives rise to a quick pulse referred to herein as “TEMP.”

Past measurements indicate that lightning strokes contain significant components with rise times < 10-7 sec. Lightning creates electric fields in the discharge region > 106 V/m, over an order of magnitude higher than the peak TEMP field, with power levels at approximately 1012 W, and energy dissipation between 109 and 1010 J. Instruments on orbiting satellites have detected many lightning bolts with currents as high as 106 A, which the above numbers do not even take into account.

A direct lightning strike produces the most severe effects. The high current density of about 103 A/cm2 in a lightning stroke delivers a high power density to the strike point resulting in demolished structures such as exploded timber, molten metal, and charred insulation. Lightning transients can propagate along transmission lines at almost the speed of light, with circuit limited rise times – 10-6 see peak voltages as high as a million volts, with a maximum rate of rise of approximately 1012 V/sec. In fact, a lightning strike on the 110-kV line of the Arkansas Power & Light Company once reached a peak voltage of 5 million volts within 2 µsec without calamitous results.

The spectacular destruction accompanying a direct lightning hit is not apt to accompany an EMP. The primary effect of the TEMP is to induce overvoltages and overcurrents in the power system. The transients produced in the system will have a slower rise time than the free wave TEMP. The newly developed zinc oxide lightning arrestors should be quite effective in shunting these pulses to ground. It has been shown that these induced voltages and currents cannot cause flashover across transmission lines, and can only do so in isolated instances for distribution lines. The TEMP excites all three phases and the ground wire(s) similarly and almost simultaneously. Thus, it cannot produce large enough voltage differences between the lines to produce breakdown. This consideration, together with those of leaders and streamers, electron time of flight, and electron avalanche imply that it is impossible for the EMP to cause widespread damage to the transmission line system, and almost as likely for the distribution grid.

Also, I saw an IEEE article written by two Chinese Engineers in Nanjing, China, entitled “Using a Second-Order Integral Equation Method to Study the High-Altitude Nuclear EMP”, Jin Zhang and Ye-Rong Zhang, IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY 2018. This article explains a second-order Integral Equation Method (IEM) introduced for the calculation of the High-altitude Electromagnetic Pulse (HEMP). Credit to China for allowing this paper to be displayed by the IEEE in the interest of science.

Stay tuned for my next article regarding how to mitigate damage from an EMP event.

4 comments on “Understanding the Electromagnetic Pulse (EMP)

  1. D Feucht
    September 17, 2018

    Steve,

    Timely topic, considering both the recent behavior of the sun and geopolitics.

    One big difference between lightning and a nuclear EMP from low earth orbit over the continental USA is that a lightning strike is highly localized, though conduction along a transmission line extends the effect. But an EMP event (as described in an EDN blog of mine at

    www dot edn dot com/electronics-blogs/outside-the-box-/4421518/The-effect-of-a-nuclear-EMP-event-on-a-dental-implant

    would not be localized and hence can affect not only power lines but any electronics not sufficiently shielded, including power-grid control electronics. So, while the lines themselves might survive, it is anything with integrated circuits that can be in trouble.

  2. Steve Taranovich
    September 17, 2018

    @D Feucht—good points–thanks for your observations—I will shortly be writing about methods to protect electronics. This is something we need to research and develop

  3. jrw001
    September 18, 2018

    My first job out of college was EMP testing for the Air Force.  I worked with 3 types of EMP testing, High Energy Pulse (Trestle), Direct Drive (Inductive), and Continuous Wave (Network Analyzer Sweep).  I helped with the EMP Test for the Air Force One Comms System and Boeing was the prime contractor (they did an amazing job).  I used the “out of place” oscope on the main panel and still smile when I see it in videos.  Damped Sinusoids are what you mostly record, the frequency range of the EMP Pulse is 100 kHz to 250 MHz.  I had a semi trailer of the latest tech to myself for years and I learned a lot and had fun.  I wrote my first C program on the uVax II and that is all I've been doing since.  Frying all electronics is a stretch but system resets etc. is real so in a war situation, put your fleet over the north pole, set off a nuke, and attack.  

                 

  4. Steve Taranovich
    September 18, 2018

    @jnwoo1—-That work must have been so cool! Thanks for sharing this excellent experience with our readers

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