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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report
state, one of the states most affected by the blackout, were expected to equal approximately $46 million during the blackout period.5
The Workshop Presentation
The first speaker at this session was Frank Koza, executive director of Systems Operations at PJM Interconnection. PJM is a regional transmission organization with 164,905 MW of generating capacity that coordinates the movement of wholesale electricity over 56,250 miles of transmission lines in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and the District of Columbia. Koza began his presentation by noting that the impacts of space weather on the power system have been well documented. Space weather can give rise to the superposition of extraneous currents onto the normal operational flows on power system equipment. This can create conditions capable of causing damage within seconds. Fortunately, the majority of the events result in relatively minor power system impacts. However, the occasional serious event can have wide-ranging impacts.
One example of a space weather event that had a major impact was the March 1989 superstorm. During this storm, a large solar magnetic impulse caused a voltage depression on the Hydro-Quebec power system in Canada that could not be mitigated by automatic voltage compensation equipment. The failure of the equipment resulted in a voltage collapse. Specifically, five transmission lines from James Bay were tripped, which caused a generation loss of 9,450 MW. With a load of about 21,350 MW, the system was unable to withstand the generation loss and collapsed within seconds. The province of Quebec was blacked out for approximately 9 hours.
Also during this storm, a large step-up transformer failed at the Salem Nuclear Power Plant in New Jersey. That failure was the most severe of approximately 200 separate events that were reported during the storm on the North American power system. Other events ranged from generators tripping out of service, to voltage swings at major substations, to other lesser equipment failures (Figure 2.2).
Koza made the point that operators of the North American power grid constantly review and analyze the potential risks associated with space weather events. Grid operators rely on space weather forecasts such as those produced by NOAA’s Space Weather Prediction Center (SWPC; see http://www.swpc.noaa.gov). They also monitor voltages and ground currents in real time and have mitigating procedures in place. PJM, as an example, has monitoring devices in place at key locations on its system, which are monitored in real time. At the onset of significant ground currents at the monitoring stations, PJM will invoke conservative operations practices that will help mitigate the impacts if the solar event becomes more severe. During these operations, flows between low-cost but more distant generating stations and load centers are reduced so as to maintain power grid stability.
What has changed since 1989? On one hand, space weather risks have declined because of increased awareness by system operators and improved forecasts. On the other hand, 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 demand centers. The magnitude of power transfers has grown, and the risk is that the increased level of transfers, coupled with multiple equipment failures, could aggravate the impacts of a storm. With respect to this trend, the long distance between Hydro-Quebec’s hydro-generation stations and load centers is one of the factors that is believed to have contributed to its space weather vulnerability.
Koza also presented his vision of a “perfect storm” space weather event. One might think that an event that occurred at peak load could produce the most severe impacts. However, at peak loads, almost all of the generators are running, and loss of a given amount of generation would have less impact on grid stability than at light load. Loss of multiple facilities at peak load, while of significant concern, can more readily be handled with emergency procedures and other well-established practices.
In Koza’s opinion, the power system is more vulnerable to a severe geomagnetic storm during a period of light load with unusually heavy transfer patterns, as is prevalent in the middle of the night during the spring and the fall. Loss of multiple facilities at lighter loads, and high levels of long-distance transfers between low-cost but more distant generating plants and load centers, set up the potential for voltage collapse with minimal ability for mitigation. If several elements were lost at strategic locations, a voltage collapse and associated blackout would be possible.