By Rich Heidorn Jr.

A utility-funded study has concluded a high-altitude nuclear explosion could cause a multi-state electric outage but not the nationwide, months-long blackout some observers have warned of.

The findings are contained in a three-year study by the Electric Power Research Institute on the impact of a high-altitude electromagnetic pulse (HEMP).

Such an attack could result in a multi-state outage, EPRI acknowledged Tuesday, but it said shielded cables, fiber optics, surge protection, enhanced grounding and modifications to substation control houses could reduce the threat.

Although the report did not provide any cost estimates for the mitigation plans, project manager Randy Horton said through an EPRI spokesman that costs could range from $500,000 to $2 million per substation.

EPRI said it conducted the report “because of the extreme differences in views among experts regarding the potential impacts” of a HEMP caused by the detonation of a nuclear weapon 30 km or more above the earth’s surface.

Under the scenarios evaluated by EPRI, “impacts such as regional disruption or damage to DPRs [digital protective relays] and regional voltage collapse could be experienced,” the researchers said. “Research findings do not support the notion of blackouts encompassing the contiguous United States and lasting for many months to years.”

The report comes little more than a month after President Trump signed an executive order requiring the government to coordinate its efforts on EMPs. The order directs the secretary of Homeland Security and other officials to identify the critical functions and infrastructure systems that could be disrupted by EMPs within 90 days.

Generation not Studied

EPRI’s report, which incorporated research from the Department of Energy’s national labs and collaboration with the Defense Threat Reduction Agency and the Electricity Subsector Coordinating Council (ESCC), was funded by some 60 utilities.

It focused on the potential impacts of a HEMP attack on the transmission system and how overhead transmission lines, substations and switchyards could be hardened. It did not look at the potential effects of HEMP attacks on “generation facilities, nuclear reactors, distribution systems, loads or other key elements or infrastructure sectors,” EPRI said, recommending those subjects for further research.

The study looked at the impacts of three “hazard fields” that can be produced by a nuclear detonation, based on the weapon’s yield and the height of the explosion above the surface:

• The early time component (E1 EMP), an intense, short-duration electromagnetic pulse characterized by a “rise time” of 2.5 nanoseconds and amplitude of up to 50 kV/meter on the ground;
• The intermediate time component (E2 EMP), an extension of the E1 EMP with an electric field pulse amplitude of about of 0.1 kV/m and a length of one microsecond to about ten milliseconds;
• The late time component (E3 EMP), a very low frequency (below 1 Hz) pulse with amplitude of tens of V/km lasting from one second to hundreds of seconds. The event would be similar to severe geomagnetic disturbances (GMDs) caused by solar flares, which can last several days.

The area exposed to E1 EMP fields would be limited by the line of sight from the weapon to the horizon; a detonation at 200 km could affect a circular area of 3 million square miles — most of the continental U.S. and portions of Canada and Mexico — albeit at different levels of severity. The pulse can “couple” to overhead lines and cables, exposing connected equipment to voltage and current surges, potentially damaging DPRs, communication systems and supervisory control and data acquisition (SCADA) systems.

EPRI said E1 EMPs would cause “moderate” damage based on modeling from Los Alamos National Laboratory of up to 25 kV/m at the most severe location on the ground. Increasing the pulse to 50 kV/m resulted in “more severe” damage.

“Based on the assumptions made in the assessments, it was estimated that approximately 5% of the transmission line terminals in a given interconnection could have a DPR that is disrupted or damaged by the nominal E1 EMP environment that was simulated, whereas approximately 15% could be impacted by the scaled (up to 50 kV/m at the most severe location on the ground) E1 EMP environment,” the report said.

Although its testing did not indicate E1 EMP impacts alone would cause immediate, interconnection-scale disruptions, “this finding is not conclusive due to uncertainties regarding how damaged DPRs might respond during an actual event … or how potential E1 EMP damage to generator controls and other systems such as automatic generation control (AGC), not included as a part of this study, might affect the long-term operation of the grid,” EPRI said.

Mitigation Measures

The researchers said their modeling and laboratory testing of DPRs indicated design changes could provide adequate mitigation up to 50 kV/m:

• Shielded control and signal cables with proper grounding;
• Low-voltage surge protection devices or filters;
• Use of fiber optics-based protection and control systems;
• Modifications to substation control houses to enhance their electromagnetic shielding; and
• Grounding and bonding enhancements.

It also recommended transmission operators maintain supplies of replacement DPRs and other critical assets.

E2 EMPs can couple to overhead lines or cables through the air, like E1 EMPs. “This coupling mechanism is similar to how the field created by a nearby lightning strike couples to an overhead transmission line,” EPRI said. But because of the low amplitude, they are unlikely to affect the transmission system. “Thus, no specific mitigation options were identified as a part of this research,” EPRI said.

But it said E2 EMPs “may be a threat for assets that operate at lower voltages (e.g., low-voltage inverters connected to rooftop PV).”

The low-frequency geomagnetically induced currents (GICs) resulting from E3 EMPs can cause magnetic saturation of transformer cores, causing transformers to generate harmonic currents, absorb reactive power and experience heating in windings and structural parts. “Potential impacts of E3 EMP on the bulk power system can include voltage collapse (regional blackout) and transformer damage due to additional hotspot heating,” EPRI said.

EPRI said E3 EMPs alone could result in a multi-state blackout, “but immediate, widespread transformer damage due to hotspot heating from part-cycle saturation is not expected to occur.”

Researchers said mitigation options used for GMD events would also be effective for E3 EMPs, including:

• Preventing protection system misoperations by modifying protection and control schemes to make them resilient to harmonics and system imbalance;
• Blocking or reducing the flow of GICs;
• Automatic removal of some shunt reactive power compensation devices such as shunt reactors and use of under-voltage load shedding (UVLS); and
• Maintaining supplies of spare large power transformers and high-voltage circuit breakers.

EPRI’s analysis of the combined effect of E1 and E3 EMPs indicated DPRs damaged by surges would not cause the immediate disconnection of transmission lines but would prevent the DPRs from performing their protection and control function.

“Significant damage to DPRs and other controls from E1 EMP would be expected to degrade recovery efforts and longer-term viability of controlling system frequency due to potential damage to AGC and other ancillary functions,” EPRI said. “These latter effects could impact the long-term stability (voltage and/or frequency) of an area affected by the HEMP attack.”

Without hardening of the transmission system, “recovering from a HEMP-induced blackout may present operators with challenges that have not been experienced following previous blackouts from more traditional causes. These potential challenges are primarily related to unavailable, inoperable or damaged equipment and impaired situational awareness capability,” EPRI said.

Recovery Efforts

The study recommended transmission operators develop alternatives to their current step-by-step facility energization procedures, noting damaged equipment may interrupt cranking paths following a HEMP event.

“Because damage to large power transformers is expected to be minimal, recovery times following a HEMP-induced blackout would be expected to be commensurate with historical large-scale blackouts if robust E1 EMP protections are deployed such that E1 EMP impacts to equipment, situational awareness, SCADA and other infrastructures that support power system restoration are minimal,” it said.

Southern Co. CEO Thomas A. Fanning, co-chair of the ESCC, said the report “greatly enhances our understanding of the potential impacts EMPs could have on our national energy grid.”

Scott Aaronson, the Edison Electric Institute’s vice president for security and preparedness, said the report “enables electric companies to make science-informed decisions for developing, testing and deploying EMP-resistant grid components.”

“EPRI also tested mitigation strategies and was able to rule out options that don’t work,” Aaronson added. “Multiple electric companies will be piloting those potential solutions to ensure new mitigation strategies do not impact other energy grid equipment or undermine or conflict with mitigation and protective measures that already are in place.”

The report said field testing of mitigation will be needed to avoid unintended consequences and obtain “realistic cost data to inform future decision making.” EPRI said it has begun a new research effort to further evaluate the mitigation options.

Dissenting View

The Secure the Grid Coalition, which claims to have former CIA Director R. James Woolsey among its members, issued a statement blasting the EPRI report as a whitewash “reminiscent of past tobacco industry-underwritten efforts to have putatively independent ‘scientists’ disinform the public about the actual dangers of smoking.”

The group said EPRI made “faulty assumptions” about the damage EMPs would cause to transformers and SCADA systems and ignored “abundant data derived by the Pentagon, civilian agencies and government-sponsored studies.”