The Sun: Friend or Foe?
As explained in the previous article “Solar Energy: The Once and Future King” the Sun, the source of life on Earth has been providing us with an inexhaustible source of energy: its irradiation. But can the Sun also be a threat? Let’s take the things from the beginning.
In Ancient Greece, by 300 B.C., Theophrastus the Athenian (“Θεόφραστος ο Αθηναίος”) had already discovered the existence of sunspots while at the same time the Chinese astronomer Kan Ten was making similar observations. From 28 B.C. until 1638 A.C., Chinese astronomers recorded 112 sunspots. On December 21st 1801, Alexander von Humboldt, author of the five-tome encyclopedia “Cosmos: A Sketch of a Physical Description of the Universe”, discovered the magnetic storms by observing magnetic disturbances and the occurrence of aurora borealis in Berlin. Another scientist, Heinrich Schwabe, was trying to discover a planet closer to the Sun than Mercury; for 17 years he was studying, detecting and recording all the shadows in the surface of the Sun (including sunspots) in an attempt to find the shadow that this planet would cast on the Sun’s surface. In 1843, by studying his archive, he noticed a pattern in the rate of sunspot appearance over a 10.4 year cycle. It was later verified that this period was almost 11 years; what we now call solar cycle. The British astronomer Richard Carrington was the first in 1859 to detect a solar flare and the magnetic storm that followed 17 hours later; the storm provoked an aurora borealis visible far away from the North Pole. Although he noticed the coincidence he did not draw any conclusions. It was George Hale who connected the dots in 1892 with the aid of a spectroheliograph; a machine of his own invention that was able to capture images of the Sun. Since then, several scientists made similar correlations and later verified that there was something propagating from the Sun to the Earth with a speed of 400-900 km/s that was causing magnetic disturbances upon its arrival. 
All the above were useful elements to fully understand the complete chain of events that lead to magnetic (or else geomagnetic) storms.
A Different Kind of Storms
There are a lot of phenomena that take place in the surface of the Sun. All of them are related in a way and they appear in periods of 11 years. The beginning of the solar cycle is defined by the minimum of this solar activity.
Let’s skip a few steps in the chemical reactions and physical processes of the Sun and jump directly to the formation of sunspots. Sunspots are dark regions of low temperature (compared to the average temperature of the Sun), where strong magnetic fields also tend to form. They last from several hours to a few months and they always appear in pairs where one sunspot is the north magnetic pole and the other one the negative. Around this magnetically active regions two more phenomena appear: the solar flares and the coronal mass ejections (CME). As a result of the last two, charged particles, mainly electrons and protons (plasma), are released from the Sun to the space thus forming the solar wind. If the solar wind moves through the interplanetary space to the direction of the Earth, then upon reaching the Earth’s magnetosphere and ionosphere, magnetic disturbances in the Earth’s magnetic field will be noticed resulting into a series of related phenomena the most popular of which is the aurora. These disturbances are called geomagnetic storms and their creation is illustrated in Fig. 2.
The charged particles arriving in the Earth’s ionosphere create a horizontal flow of charge (electrojet) fluctuating in time. This current in its turn creates a fluctuating magnetic field. As Faraday’s law states, a changing magnetic field induces an electric field that drives currents on conductive loops. In this case a geomagnetic field induces a geoelectric field and thus geomagnetically induced currents (GID) appear on grounded conductors such as the electrical power lines and other pipelines ,.
Power System Faults
The frequency of the GIC ranges from 10 kHz to a few Hz which compared to the 50 or 60 Hz of the grid frequency render GIC as direct currents (dc) or quasi-dc to be exact. Subsequently, GIC travelling through the transmission lines will reach the transformers at the end of the lines as quasi-dc currents. There, due to the fact that dc current will be added to the ac magnetizing current of the transformer, a distortion of the ac current waveform is to be expected leading the transformer in saturation. Harmonics can also be introduced into the system and other faults such as overheating, voltage anomalies and false trippings may occur. A summary of the cascaded faults is presented in Fig. 3.
Numerous events of geomagnetic storms have been recorded, a detailed list of which is provided in .
- The first record of a geomagnetic storm goes back to 1847 where the aurora borealis was visible in the south England and was accompanied by interruptions in the telegraph lines.
- In 1859, one of the most powerful geomagnetic storms in our recorded history took place, known as the Carrington event. In Boston, Portland and central Europe several disturbances were reported by the telegraph operators.
- In 1921 in Sweden, several telegraph stations caught fire during a geomagnetic storm.
- On March 24th 1940, power system disturbances (voltage dips, reactive power swings and tripping of transformer banks) were for the first time recorded in the US and Canada while at the same time telegraph equipment in Norway caught fire.
- On February 10th 1958, a blackout hits Toronto and abnormal power flows are noticed in Minessota.
- On August 4th 1972, an outage of the phone cable system in the US was accompanied by several problems in the country’s power systems (voltage fluctuations, tripping of equipment and quasi-dc currents of 100 A at transformer neutral to ground connections).
- On March 13th 1989, a violent geomagnetic storm hit the Earth. Within 90 seconds the whole province of Quebec was experiencing a major 9 hours blackout . Power stations in northern USA were also affected. Before this event little attention was given to the impact of geomagnetic storms. The problems faced by electric utilities during this storm served as the basis for future studies. A complete analysis of this event is provided in .
- On October 30th 2003, a geomagnetic superstorm in the south of Sweden left the city of Malmö in complete darkness for one hour . The event was known as the Halloween Storms.
- On July 23rd 2012, a powerful coronal mass ejection took place. The unleashed solar wind missed the Earth by 9 days. If it had reached the Earth it would have been one of the biggest geomagnetic storms in history.
If a Carrington level geomagnetic storm was to be repeated in North America, according to a study held in 2013 , the estimated cost would be around $0.6 - 2.6 trillion USD depending on the damages caused to the transformers.
In order to mitigate the effects of geomagnetic storms on electrical power systems a series of solutions have been implemented over the years. One solution would be to use protective relays to isolate transformers once a GIC fault has occurred but it is yet technically quite difficult to accurately detect a GIC fault thus increasing the chances of a false alarm that would trip the relay. Another solution would be the installation of series capacitors in transformer neutrals and transmission lines. However, the exorbitant cost of such a solution has left the utilities with no other option than to develop operational guidelines in case of a geomagnetic storm. Consequently, the most feasible protective action is to rely on the advanced metering and forecasting techniques provided by data from high-tech satellites such as the Solar and Heliospheric Observatory (SOHO).
A future threat?
In order to tackle the intermittent nature of renewable energy sources and strengthen the grid stability and reliability, electrical power networks become more and more interconnected. However, they are growing to be more and more vulnerable to GIC since the longer transmission lines that are being installed, expose the grid to larger GIC .
As we enter 2019, a year that marks the beginning of the 25th solar cycle, we should remain vigilant as even numbered solar cycles tend to be cycles with increased solar activity. Further research is needed in order to protect the largest and most complex machine ever built: our electrical power network. The scientific community has long underestimated the threat from geomagnetic storms. Events like the blackout of 1989 in Quebec serve as alarms for utilities. Let’s not ignore them.
References E. Theodosiou, E. Danezis, Το Σύμπαν που Aγάπησα - Τόμος Α’ [The Universe I Loved – Part A’], Athens: Diaulos, 1999.  K. Baumgartner, National Geographic, https://www.nationalgeographic.com/photography/photo-of-the-day/2009/6/tundra-aurora-pod/ .  https://www.noaa.gov/explainers/space-weather-storms-from-sun .  W. A. Radasky, “Overview of the impact of intense geomagnetic storms on the U.S. high voltage power grid” in 2011 IEEE International Symposium on Electromagnetic Compatibility, 2011, pp. 300–305.  O. Samuelsson, “Geomagnetic disturbances and their impact on power systems”, Status report, 2013.  National Oceanic and Atmospheric Administration, U.S. Department of Commerce, https://www.weather.gov/akq/SpaceWeather .  D. H. Boteler, R. J. Pirjola, and H. Nevanlinna, “The effects of geomagnetic disturbances on electrical systems at the Earth’s surface”, Adv. Space Res., vol. 22, no. 1, pp. 17–27, Jan. 1998.  J. G. Kappenman, W. A. Radasky, J. L. Gilbert, and L. A. Erinmez, “Advanced geomagnetic storm forecasting: a risk management tool for electric power system operations”, IEEE Trans. Plasma Sci., vol. 28, no. 6, pp. 2114–2121, Dec. 2000.  L. Bolduc, “GIC observations and studies in the Hydro-Québec power system”, J. Atmospheric Sol.-Terr. Phys., vol. 64, no. 16, pp. 1793–1802, Nov. 2002.  A. Pulkkinen, S. Lindahl, A. Viljanen, and R. Pirjola, “Geomagnetic storm of 29–31 October 2003: Geomagnetically induced currents and their relation to problems in the Swedish high-voltage power transmission system”, Space Weather, vol. 3, no. 8, Aug. 2005.  Lloyd’s, “Solar storm risk to the North American electric grid”, Report, 2013.  NASA/GSFC/SDO, https://www.flickr.com/photos/gsfc/7931831962/in/photostream/