EMP Threat Real but Limited, EPRI Says in Much-Anticipated Report

Depending on the hazard field, electromagnetic pulses (EMPs) resulting from detonation of a nuclear weapon at high altitude or in space could cause significant damage to electronics on the bulk power system and even prompt a regional voltage collapse, the Electric Power Research Institute (EPRI) says in much-anticipated findings from its three-year study on high-altitude EMPs (HEMPs).

However, the research does not support notions that a HEMP event could cause a crippling nationwide blackout that could last for many months to years, as some experts have warned for years, EPRI said.

EPRI's April 30-released report is geared mainly toward asset owners and operators of the U.S. bulk power system, though it is also designed to inform regulators and policymakers. By furnishing the power sector with options for mitigating potential HEMP impacts that it identified, its primary aim is to help stakeholders make "more informed" decisions regarding the threat of a HEMP attack on the U.S. grid.

The findings come barely a month after President Trump signed an executive order to boost coordination for and national resilience against EMP threats-both from nuclear warfare and natural events like solar superstorms. Warning that EMPs could debilitate critical infrastructure and have implications for national security, the order lays out an assortment of actions for the Departments of Energy (DOE), Defense, Homeland Security, and Commerce to incentivize action to strengthen "vulnerable priority critical infrastructure" by the private sector-including through guidance and regulations.

The agencies, for example, must share technical expertise and data with the private sector and develop plans to mitigate the effects of EMPs within 90 days of the order. And within a year, the DOE must review existing standards for EMPs and "develop or update" quantitative benchmarks that describe the physical characteristics of EMPs, including waveform and intensity.

Uncertainties Remain

But while the order suggests new federal mandates to protect critical infrastructure against EMP events and attacks may be on the horizon, EPRI's report outlines a broad range of uncertainties that it identified during its three-year effort.

EPRI uses the International Electrotechnical Commission's (IEC's) definitions for HEMP hazard fields. EMP components are referred to as E1, E2, and E3. E1-a "fast pulse"-consist of intense, short-duration EMPs characterized by a rise time of 2.5 nanoseconds and amplitude on the order of tens of kV/m, and up to 50 kV/m at the most severe location on the ground. E2, which is similar to lightning, have field pulse amplitudes of about 0.1 kV/m, lasting 1 microsecond to 10 milliseconds. E3-a "slow pulse"-are at very low frequencies of below 1 Hz with amplitudes on the order of tens of V/km, lasting 1 second to hundreds of seconds.

E1 EMP fields "can be quite large," EPRI said, but the area of coverage depends on where the nuclear weapon explodes. "For example, a detonation at 200 km can affect a circular area of on the order of 3 million square miles. However, not all areas included within the circular region experience the maximum electric field, and strength of the field falls off with distance from the ground zero location." Its impact can be severe. If it couples to overhead lines and cables, it can expose connected equipment to voltage and current surges, and radiate equipment directly. Potential impacts include moderate disruption or damage of electronics, including digital protective relays (DPRs), communication systems, and supervisory control and data acquisition (SCADA) systems, and they could affect "large areas such as an electrical interconnection."

However, E1 impacts were not found to cause immediate interconnection-scale disruption or blackout of the grid-though EPRI noted that finding was not conclusive owing to uncertainties about how damaged DPRs might respond during an actual event, or how damage to generator controls and other systems might affect long-term operation of the grid. Among mitigative options EPRI outlined for a 50-kV/m threat level are to shield control/signal cables with proper grounding; to install low-voltage surge protection devices and filters; and to modify substation control houses.

E2 EMPs do not couple to overhead lines or cable, though they could couple to conductors through the air like an E1. Still, because the amplitude is low, "impacts to the transmission system are not expected to occur," EPRI said. That's why it recommended no mitigation options for this hazard field.

E3 EMPs, perhaps the most insidious threat, induce low-frequency (quasi-DC) currents in transmission lines and transformers. "The flow of these geomagnetically induced currents (GICs) in transformer windings can cause magnetic saturation of transformer cores, which causes transformers to generate harmonic currents, absorb significant quantities of reactive power, and experience additional hotspot heating in windings and structural parts," EPRI warned. "Potential impacts of E3 EMP on the bulk power system can include voltage collapse (regional blackout) and transformer damage due to additional hotspot heating." Among mitigative options it identified for E3 are similar to those to guard against GMD events. They include:

• Avoiding protection system misoperations by modifying protection and control schemes to be resilient to harmonics and system imbalance.
• Blocking or reducing the flow of GICs.
• Automatic removal of some shunt reactive power compensation devices, for example shunt reactors, and/or employing under-voltage load shedding (UVLS).
• Sparing of large power transformers and high-voltage circuit breakers.

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," EPRI said.

Industry Wants to Make Decisions Based on 'Sound Science'

EPRI's findings are significant because experts have speculated about HEMP impacts for years, citing limited EMP field tests. These include the 1962 Starfish Prime high altitude burst nuclear test 900 miles from Hawaii, which knocked out 36 strings of streetlights and set off burglar alarms, and tests by the former Soviet Union in Kazakhstan in 1961 and 1962, which reportedly caused damage to communications systems, the power supply, and safety devices. William Graham, chairman of the former EMP Commission, established by Congress in 2001, in July 2017 concluded in a report that "even for a low-yield 10 to 20 kiloton weapon, the EMP field should be considered for unprotected U.S. systems."

But experts, like Dr. George Baker, professor emeritus at James Madison University and director for the foundation for resilient societies, have warned that industry is reluctant to harden against EMPs because there are no current EMP/GMD regulations or requirements for civilian infrastructure. "Power industry officials have expressed reservations that any near-term protection initiatives could well be rendered obsolete if they don't conform to unknown future regulations and standards," Baker said. Cost is another factor. "Generation stations have not been addressed because of cost-recovery limitations (unlike transmission systems where federal regulations allow cost recovery)," Baker testified on Feb. 27 before a Senate committee.

On Monday, Michael W. Howard, president and CEO of EPRI, said EPRI's research represents "the largest utility collaborative on this issue focused on understanding the technical facts using both laboratory testing and advanced modeling." The results also "provide a cost-effective pathway to enhance the resilience of the grid and accelerate recovery. EPRI's research continues to support the very high priority that the electric utility industry places on providing reliable electricity for all customers," he said.

The power industry, meanwhile, says it works closely to share threat information and partner with all levels of government to mitigate and respond to national-level incidents to critical infrastructure. However, the Edison Electric Institute (EEI), which includes all U.S. investor-owned power companies, has urged regulators to remember that how an EMP may impact critical infrastructure is "an extremely complex issue that cannot be solved with a one-size-fits-all solution."

On Monday, EEI Vice President for Security and Preparedness Scott Aaronson told POWER that EPRI's research will enable "electric companies to make science-informed decisions for developing, testing, and deploying EMP-resistant grid components. Sound policy should be informed by sound science."

-Sonal Patelis a POWER associate editor (@sonalcpatel, @POWERmagazine)

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