The Electric Power Research Institute (EPRI) released findings from a three-year study of potential impacts of high-altitude electromagnetic pulses (EMP) on the electric transmission system.

The report, High-Altitude Electromagnetic Pulse and the Bulk Power System—Potential Impacts and Mitigation Strategies, includes results from laboratory testing and analysis of potential EMP impacts on the electric transmission system.

EPRI completed a three-year study of potential impacts that a nuclear explosion might have on the electric power grid. Source: NRELEPRI completed a three-year study of potential impacts that a nuclear explosion might have on the electric power grid. Source: NRELThe research focused on the impact to the U.S. electric power grid should a nuclear device detonate above the atmosphere.

According to the report, an EMP event can be caused by a nuclear explosion above Earth’s atmosphere that propels electromagnetic energy towards the surface, generating an initial, short-duration pulse (known as E1); an intermediate pulse with characteristics similar to those caused by nearby lightning strikes (E2); followed by a late pulse (E3) which is similar to a severe geomagnetic disturbance caused by solar flares.

Key research findings for the initial pulse include:

  • Transmission electronic equipment damage or disruption can result from induced voltage surges in connecting cables, as well as by direct exposure to the initial pulse.
  • Digital protective relays – devices that help detect faults in the electric system – were generally resilient to direct exposure to the initial pulse but were found to be vulnerable to the surges induced on control and communication cables.

The research indicated that initial pulse impacts could be mitigated through various options including:

  • Shielded cables with proper grounding;
  • Low-voltage surge protection devices and/or filters;
  • Use of fiber optics-based communications;
  • Enhanced electromagnetic shielding of electric substation control houses; and
  • Grounding and bonding enhancements.

The research also showed that the combined effects of the initial and late pulses could trigger a regional service interruption but would not trigger a nationwide grid failure. Recovery times are expected to be similar to those resulting from large-scale power interruptions caused by other events provided that mitigations specific to the initial pulse are deployed. Possible damage to large power transformers was found to be minimal.

For an intermediate pulse, the system impacts are minimal, if any, and the study finds no further mitigation options are recommended.

The research was backed by funding and support from more than 60 U.S. utilities, and collaboration with the Defense Threat Reduction Agency, the U.S. Department of Energy and the Electricity Subsector Coordinating Council (ESCC), which provides national coordination of government and utility preparation and response to disasters affecting the power system.

EPRI said it is working with utilities to further evaluate mitigation options for the initial pulse, including additional testing to more fully understand performance and reliability.