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In November of 2020, The Electric Power Research Institute (EPRI) published a publicly-available document titled, “High-Altitude Electromagnetic Pulse Hardening Pilot Projects: Status and Future Research”. In this document, EPRI details the results of a 3-year study that concluded in April of 2019 on the potential impacts of a high-altitude electromagnetic pulse (HEMP) on the electric transmission system. The document reviews the HEMP environment, including the early, mid, and late time (E1, E2, and E3) waveforms and potential susceptibilities of the grid. To learn more about the HEMP environment, you can find our 3-part blog series on the subject here: APELC blog.

APELC is proud to say that our 2m RS105 system (shown in Figure 1) is featured prominently in this article as an example of a system used for radiated susceptibility testing of grid components against the HEMP E1 waveform detailed in MIL-STD-461G. This system was the beginning of APELC supplying EPRI with systems for HEMP testing, including several pulse generators for pulsed-current and pulsed-voltage injection of the MIL-STD-188-125 E1 waveform. Examples of these units can be seen on our website along with specifications and measured waveforms.

Figure 1 APELC 2m RS105 system at EPRI

Figure 2 Unclassified free-field EMP time domain waveform for the E1 pulse (IEC 61000-2-9 and MIL-STD-461G)

The work being done by EPRI using this equipment is crucial for securing the power and utility infrastructure of our nation. Although the U.S. Department of Defense (DoD) has invested extensively in research and development to protect military critical infrastructure, the resulting guidelines outlined in MIL-STD-188-125 are often challenging and financially burdensome for civilian utilities to implement, especially considering the magnitude of the problem. EPRI’s efforts have resulted in recommendations and guidelines that their utility customers can use to identify practical and cost-effective methods of shielding, filtering, and safeguarding our nation’s grid against the threat of a high-altitude nuclear event.

The field of pulsed power has significant historical connections to HEMP testing. Prior to the nuclear test ban treaty in 1963, the United States conducted high-altitude nuclear tests over the Johnston and Bikini Atolls. One of these tests, known as Starfish Prime, provided valuable insights to U.S. scientists regarding the impact of an HEMP event on utilities. For instance, immediately after the blast, multiple strings of streetlights on the Hawaiian island of Oahu (located 800 miles away) went completely dark. Researchers at Sandia National Laboratories analyzed the event and determined that due to the detonation’s azimuthal angle relative to the streetlight powerlines, an electric field exceeding 5kV/m was present at that location. This electric field was sufficient to cause the observed damage in the lights and associated infrastructure.

Measurements and theoretical calculations from these tests gave rise to some of the classified and unclassified waveforms used to describe the HEMP environment. Using the unclassified E1 waveform from IEC-61000-2-9 as an example (Figure 2), we can see that the shape is a classic double-exponential, with a fast rise-time (~2ns) compared to the falling edge or pulse width (~25ns). Coincidentally, this type of waveform is exactly what a capacitive discharge circuit produces- making the Marx generator an ideal means of recreating these threat-level waveforms.

APELC is in our 25th year of making Marx generators and other pulsed power components/systems for applications including HEMP testing, and we are always looking for a new challenge! If you have a question about how we can help with HEMP or similar testing at your facility, don’t hesitate to reach out to us at



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