CHAMPAIGN, Ill. - Geomagnetic storms have the potential to disrupt and damage electrical infrastructure, leading to serious consequences for installations and surrounding communities. For this reason, the U.S. Army Installation Management Command asked the Engineer Research and Development Center to assess Army energy systems’ vulnerability to these events.
A geomagnetic storm is a solar-related global phenomenon that can last several days and can affect multiple continents. Geomagnetic storm impacts are a low probability-high criticality concern that is increasing in near-term likelihood due to the nation’s reliance on and type of electricity use, expanding use of automated power controls, and cyclic changes in solar activity. Possible adverse installation impacts include an unscheduled loss of electrical service for hours to months and damage to transformers, computers, communications networks and Supervisory Control and Data Acquisition networks.
Geomagnetic storms are caused by coronal mass ejections (CME) impacting the Earth’s magnetosphere. CMEs are explosive releases of enormous quantities of charged particles and electromagnetic radiation from the sun. A CME disturbs the Earth’s magnetic field as can sometimes be seen by the display of an aurora (northern and southern lights).
When the charged particles enter the earth’s atmosphere, unevenly distributed electrical currents can build up in the earth’s crust. These geomagnetic induced currents (GIC) are especially a concern when they find a man-made path of lower resistance (as compared to the earth itself) in long metal conductors such as electrical lines, communication lines, and pipelines. Direct currents as high as 300 amperes in the neutral of some transformers have been reported. This is enough stray current to damage equipment far from the source of the intrusion. The geomagnetic storm on March 13-14, 1989 led to a power outage in the entire Province of Quebec, Canada, and in parts of the Northeastern United States
Several factors influence the impact of GICs on the electric grid. These include line length and orientation, line resistance, ground resistance, transformer design and quality of electrical infrastructure. GICs are more prominent at higher latitudes (near the poles of the Earth); however, GICs have been reported at middle and lower latitudes. The GIC situation can be serious near the coasts where highly conductive seawater interfaces with poorly conductive ground.
Electric system configuration is another consideration:
- Long electrical lines serve as antennas that collect GICs. Greater line length poses an increased risk because of the voltage difference at the grounded ends.
- GICs cause partial saturation of power transformer cores, which results in transformer heating and distortion of the alternating current waveform leading to faulty operation of relays and other equipment
- The impact of GICs depends on the specific transformer design. Transformers with a wye (or “star”) wiring configuration with a grounded neutral are more susceptible to GICs than transformers with a delta wiring configuration. Extra high voltage (more than 345,000 volts) transformers are particularly vulnerable to GICs
- Aging electrical infrastructure, such as transformers, tend to be more susceptible to failure. Repeated exposures to GICs can cause cumulative damage that ultimately can lead to transformer failure.
While geomagnetic storms are unpredictable, the U.S. National Oceanic and Atmospheric Administration provides information on space weather conditions ( http://www.swpc.noaa.gov ). Through the agency’s product subscription service, registered users can receive alerts, warnings, watches, forecasts, and summaries via email within moments of an event being detected.
Experts recommend a mix of hardening (material/physical) infrastructure and operational strategy (nonmaterial) measures to reduce vulnerability to and consequences of severe geomagnetic storms. With enough advanced warning, installations can implement contingency plans modifying the way they operate during severe geomagnetic storms to even include total shutdown and physical disconnection of vulnerable systems. These contingency plans may well need to be dynamic to take into account electrical and communications systems design and condition, mission criticality and the need to continue operations during an event, and an ability to recover should damage occur.