The highly complex, interconnected North American power grid has provided a long record of reliable, secure delivery of electric power. Industry has a long record of reliable operation and addressing natural risks that could affect reliability. It is because of this commitment, a North American Electric Reliability Corp. (NERC) task force was formed to address solar storm, or geomagnetic disturbance (GMD) events, which can disrupt normal power grid operations.

NERC's 2012 Special Reliability Assessment Interim Report: Affects of Geomagnetic Disturbances on the Bulk Power System indicates the most likely result from a severe GMD is voltage instability. The stability of the bulk power system can be affected by changes in reactive power profiles and extensive waveform distortions from harmonics of alternating current, both from half-cycle saturated high-voltage transformers. The potential effects include overheating of auxiliary transformers, improper operation of relays and heating of generator stators, along with potential damage to reactive power devices and filters for high-voltage dc lines.

According to scientists, solar coronal holes and coronal mass ejections (CME) are the two main categories of solar activity that drive solar magnetic disturbances on Earth. CME create a large mass of charged solar energetic particles that escape from the sun's halo (corona), traveling to Earth between 14 and 96 hours. Geomagnetic-induced currents that interact with the power system appear to be produced when large CME occur and are directed at Earth.

NERC's report identifies 33 recommendations to mitigate the impact from large GMDs. NERC and EPRI have begun work on these recommendations to provide users, owners and operators of the bulk power system enhanced knowledge and expertise to address GMDs and ensure the grid's continued reliable operation.

Immediate follow-on actions include updating NERC's May 2010 GMD alert and enhancing system operator training with GMD coursework. For more information, contact Eric Rollison at eric.rollison@nerc.net.