POWER GRIDS

Future Vulnerability

Severe space weather has the potential to pose serious threats to the future North American electric power grid.2 Recently, Metatech Corporation carried out a study under the auspices of the Electromagnetic Pulse Commission and also for the Federal Emergency Management Agency (FEMA) to examine the potential impacts of severe geomagnetic storm events on the U.S. electric power grid. These assessments indicate that severe geomagnetic storms pose a risk for long-term outages to major portions of the North American grid. John Kappenman remarked that the analysis shows “not only the potential for large-scale blackouts but, more troubling, … the potential for permanent damage that could lead to extraordinarily long restoration times.” While a severe storm is a low-frequency-of-occurrence event, it has the potential for long-duration catastrophic impacts to the power grid and its users. Impacts would be felt on interdependent infrastructures, with, for example, potable water distribution affected within several hours; perishable foods and medications lost in about 12-24 hours; and immediate or eventual loss of heating/air conditioning, sewage disposal, phone service, transportation, fuel resupply, and so on. Kappenman stated that the effects on these interdependent infrastructures could persist for multiple years, with a potential for significant societal impacts and with economic costs that could be measurable in the several-trillion-dollars-per-year range.

Electric power grids, a national critical infrastructure, continue to become more vulnerable to disruption from geomagnetic storms. For example, the evolution of open access on the transmission system has fostered the transport of large amounts of energy across the power system in order to maximize the economic benefit of delivering the lowest-cost energy to areas of demand. The magnitude of power transfers has grown, and the risk is that the increased level of transfers, coupled with multiple equipment failures, could worsen the impacts of a storm event.

Kappenman stated that “many of the things that we have done to increase operational efficiency and haul power long distances have inadvertently and unknowingly escalated the risks from geomagnetic storms.” This trend suggests that even more severe impacts can occur in the future from large storms. Kappenman noted that, at the same time, no design codes have been adopted to reduce geomagnetically induced current (GIC) flows in the power grid during a storm. Operational procedures used now by U.S. power grid operators have been developed largely from experiences with recent storms, including the March 1989 event. These procedures are generally designed to boost operational reserves and do not prevent or reduce GIC flows in the network. For large storms (or increasing dB/dt levels) both observations and simulations indicate that as the intensity of the disturbance increases, the relative levels of GICs and related power system impacts will also increase proportionately. Under these scenarios, the scale and speed of problems that could occur on exposed power grids have the potential to impact power system operators in ways they have not previously experienced. Therefore, as storm environments reach higher intensity levels, it becomes more likely that these events will precipitate widespread blackouts in exposed power grid infrastructures. The possible extent of a power system collapse from a 4800 nT/min geomagnetic storm (centered at 50° geomagnetic latitude) is shown in Figure 7.1. Such dB/dt levels—10 times those experienced during the March 1989 storm—were reached during the great magnetic storm of May 14-15, 1921.

The least understood aspect of this threat is the permanent damage to power grid assets and how that will impede the restoration process. Transformer damage is the most likely outcome, although other key assets on the grid are also at risk. In particular, transformers experience excessive levels of internal heating brought on by stray flux when GICs cause a transformer’s magnetic core to saturate and to spill flux outside the normal core steel magnetic circuit. Kappenman stated that previous well-documented cases have involved heating failures that caused melting and burn-through of large-amperage copper windings and leads in these transformers. These multi-ton apparatus generally cannot be repaired in the field, and if damaged in this manner, they need to be replaced with new units, which have manufacture lead times of 12 months or more. In addition, each transformer design can contain numerous subtle design variations that complicate the calculation of how and at what density the stray flux can impinge on internal structures in the transformer. Therefore the ability to assess existing transformer vulnerability or even to design new transformers that can tolerate saturated operation is not readily achievable.



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