GMD – Geomagnetic Disturbance

Many times each year, the sun ejects a portion of its coronal mass into space.  If the highly- energetic, electrically and magnetically charged matter characteristic of these Coronal Mass Ejections (CMEs) encounters the Earth it distorts the Earth’s geomagnetic field, inducing potentially damaging GIC (Geomagnetically Induced Current) in long transmission lines and transformers, the “ligaments” of a national-scale power grid.

Severe Space Weather-induced Geomagnetic Disturbance (GMD) can last anywhere from several minutes to several days.   Depending on the magnitude and duration of unplanned, transient current and the design and condition of transformers, especially the critical Extra High Voltage (EHV) transformers, voltage instabilities and transformer damage or degradation can occur.

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In modern times, satellite-based sensors observe powerful Coronal Mass Ejections relatively frequently.  Historically, the frequency at which powerful CMEs have affected the earth is estimated as once per 100 – 200 years.  The largest CME-event in relatively recent history, the “Carrington Event,” occurred in 1859, followed 62 years later by another event of similar magnitude, the 1921 “Railroad Storm.”  Although both events caused serious damage to the global telegraph network and the related systems that existed at those times, effects of similar storms on modern power grids would be incomparable.

Such an event almost took place quite recently, when a Coronal Mass Ejection occurred in July, 2012.  According to researchers from the National Aeronautics and Space Administration (NASA), if the eruption had occurred one week earlier massive clouds of magnetized plasma would have struck the earth. The resulting geomagnetic storm, according to NASA scientist Daniel Baker, would have been at least as strong as the Carrington event.

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