BOX 7.1 PREDICTING GEOMAGNETICALLY INDUCED CURRENTS ON THE POWER GRID: AN EXAMPLE OF A CRITICAL NATIONAL NEED
A geomagnetic storm is caused by energetic streams of particles and magnetic flux that originate from the Sun and impact and distort Earth’s magnetic field. The transient changes in Earth’s magnetic field interact with the long wires of the power grid, causing electrical currents to flow in the grid. The grid is designed to handle AC currents effectively, but not the DC currents induced by a geomagnetic storm. These currents, called geomagnetically induced currents (GICs; also known as ground-induced currents), cause imbalances in electrical equipment, reducing its performance and leading to dangerous overheating.1
Solar and space physicists, working with bulk power grid engineers, have helped to create the capability to model the effects of GICs on electricity transmission and distribution systems. This crucially important work relies on a body of knowledge built up over years of study. Today, sophisticated modeling software is used to assess the response of the electrical power system to geomagnetic storms, to assess the system’s vulnerabilities, and to develop mitigation strategies, an important example of which is work to develop sensors that can detect transformer saturation (via harmonic detection) and overheating. With this information, operators can take steps to protect costly (on the order of $10 million) and difficult-to-replace transformers. In addition, in response to the prediction of intense geomagnetic disturbances, utilities will be able to pre-position replacement equipment at key locations of high vulnerability. Such measures are critical to restoration of bulk power capabilities after disruption from a possibly crippling space weather event.
The electric power industry continues to rely on the latest developments in space weather forecasting and thus would benefit directly from implementation of the research- and applications-related programs that are recommended in this report.
1Adapted from National Research Council, Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report, The National Academies Press, Washington, D.C., 2008.
precision depend fundamentally on conditions in the ionosphere that alter the paths and properties of radio waves of all frequencies, including Global Positioning System (GPS) signals.
2. Preserve the space environment, in part by pursuing “research and development of technologies and techniques … to mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment” and by leading “the continued development and adoption of international and industry standards to minimize debris.” Satellite drag is relevant to orbit and reentry prediction and to long-term mitigation of orbital debris. The recent inability, for example, to forecast the demise of the Upper Atmosphere Research Satellite (UARS) spacecraft underscores limitations in current capabilities for modeling and understanding the interaction of Earth-orbiting objects with the upper atmosphere. Space junk now exceeds 22,000 objects larger than a softball (Figure 7.1); collisions are expected to become more frequent (and may have propelled the UARS satellite into a less stable orbit).
2 National Research Council reports Severe Space Weather: Understanding Societal and Economic Impacts: A Workshop Report (2008) and Limiting Future Collision Risk to Spacecraft: NASA’s Meteoroid and Orbital Debris Programs: An Assessment of NASA’s Meteoroid and Orbital Debris Programs (2011), both published by The National Academies Press, Washington, D.C.
3 Committee for Space Weather, Office of the Federal Coordinator for Meteorological Services and Supporting Research, National Space Weather Program Strategic Plan, FCM-P30-2010, August 17, 2010, available at http://www.ofcm.gov/nswp-sp/fcm-p30.htm.