Geomagnetic Disturbances

Geomagnetic disturbances (GMD) occur when solar storms on the sun’s surface send electrically charged particles toward earth, where they interact with earth’s magnetic field. This interaction potentially has implications for the nation’s high-voltage transmission grid. GMD can send geomagnetically induced currents (GIC) through transmission lines, potentially through transformers and into the earth through ground connections.

If the intensity and duration of a disturbance is sufficient, these abnormal electric currents may reduce system voltage and in the worst case, cause a widespread power outage. In the extreme, severe GIC can overheat transformer cores and lead to equipment damage or failure.

Solar storms typically occur in 11-year cycles. Solar Cycle 24 began in 2008 and the solar storm frequency during this cycle is expected to peak in 2013. During more than a century of operation, American Electric Power’s (AEP) system has experienced numerous geomagnetic disturbances. In that time some temporary effects have been observed, but there has been no lasting damage or consequences. AEP is less susceptible than utilities closer to the earth’s magnetic poles or in areas with more rocky soils.

AEP Transmission's GMD Preparations

AEP mounted GIC monitors on power transformers during two previous cycles and detected GIC, but there was no evidence of lasting adverse impact. In anticipation of Solar Cycle 24, AEP Transmission has taken steps to learn more about the phenomenon and proactively taken precautions by:

  • addressing GIC risks in new transformer specifications;
  • studying the AEP system to identify potential GIC vulnerability;
  • installing monitors to evaluate GMD impact at multiple locations;
  • participating in the evaluation of GMD "blocking" equipment;
  • evaluating the risks and remedies for satellite communication disruptions;
  • updating operating procedures to mitigate risks; and
  • collaborating with the Electric Power Research Institute (EPRI), the North American Electric Reliability Corporation (NERC) and the Department of Energy (DOE) to share knowledge, insights and evaluate equipment and methods to mitigate GMD.

Additionally, AEP has business continuity plans in place to sustain essential operations, 24/7 Transmission Operations Centers with back-up power sources on-site and regularly conducts drills of the AEP System Restoration Plan to enable resumption of normal operations, should an abnormal condition occur.

Geomagnetic Disturbance Q&A

  • What is a geomagnetic disturbance?

    A geomagnetic disturbance or GMD occurs when solar storms on the sun’s surface send electrically charged particles toward earth, where they interact with the earth’s magnetic field.

  • What are the risks to transmission systems from GMD.

    When these electrically charged particles interact with the earth’s magnetic field it has potential implications for the nation’s high-voltage transmission grid. GMD can send geomagnetically induced currents or GIC through transmission lines, potentially through transformers and into the earth through ground connections.

  • What is the effect of GIC on transmission systems?

    If the intensity and duration of a disturbance is sufficient, these abnormal electric currents may reduce system voltage and in the worst case, cause a widespread power outage. In the extreme, severe GIC can overheat transformer cores and lead to equipment damage or failure.

  • Are certain voltages more vulnerable than others?

    Higher voltages, such as those used in the transmission grid, are more vulnerable than the lower voltages use in the distribution system that brings power into people’s homes.

  • Is GMD more of a problem now than in years past?

    Solar activity is cyclical and peaks, increases in frequency, approximately every 11 years. We are currently in Solar Cycle 24 that began in January 2008.

    Solar Cycle 24 is predicted to be an average solar cycle and there are no extraordinary risks associated with its peak in 2012-2014. 

  • What is AEP's experience with solar storms?

    During its century of operation, American Electric Power’s (AEP) transmission system has experienced numerous geomagnetic disturbances. In that time some temporary effects have been observed, but there has been no lasting damage or consequences. AEP is less susceptible than utilities closer to the earth’s magnetic poles or in areas with more rocky soils.

  • What preparations has AEP made for this next cycle of storms?

    AEP mounted GIC monitors on power transformers during two previous cycles and detected GIC, but there was no evidence of lasting adverse impact. In anticipation of Solar Cycle 24, AEP Transmission has taken steps to learn more about the phenomenon and proactively taken precautions by:

    • addressing GIC risks in new transformer specifications;
    • studying the AEP system to identify potential GIC vulnerability;
    • installing monitors to evaluate GMD impact at multiple locations;
    • participating in the evaluation of GMD “blocking” equipment;
    • evaluating the risks and remedies for satellite communication disruptions;
    • updating operating procedures to mitigate risks; and
    • collaborating with the Electric Power Research Institute (EPRI), the North American Electric Reliability Corporation (NERC) and the Department of Energy (DOE) to share knowledge, insights and evaluate equipment and methods to mitigate GMD.
  • How does GMD impact other systems that support the transmission system?

    During peak activity, solar flares can disrupt satellite communications. This can temporarily affect global positioning systems and time synchronization signals. Improvements are being developed to enable modern communications systems to survive most solar disturbances.

The Solar Cycle

GMD: Geomagnetic Disturbances -- Interactions betweens electrically charged particles from the sun's surface and the earth's magnetic field, caused by solar storms.
GIC: Geomagnetically Induced Currents -- Electrical currents created in transmission lines and other electrical systems caused by geomagnetic disturbances.

Read more: NASA's current solar cycle prediction