Long-Term Power Transmission Failures in Southeastern Brazil and the Geophysical Environment

High-voltage transmission networks represent a large electrical circuit just above the ground subjected to a number of transient overcharges of various kinds, some of which may lead to failures. Some failures might be related to anomalies of the geophysical environment. We have analyzed one unpreced...

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Bibliographic Details
Published in:	Surveys in geophysics Vol. 33; no. 5; pp. 973 - 989
Main Authors:	Duro, Magda A. S., Kaufmann, Pierre, Bertoni, Fernando C. P., Rodrigues, Emilio C. N., Filho, José Pissolato
Format:	Journal Article
Language:	English
Published:	Dordrecht Springer Netherlands 01-09-2012 Springer Springer Nature B.V
Subjects:	Astronomy Atmosphere Cosmic rays Earth and Environmental Science Earth Sciences Earth, ocean, space Exact sciences and technology Geophysics Geophysics/Geodesy Internal geophysics Ionosphere Lightning Magnetic fields Observations and Techniques Power supply Solar activity Solar physics South America Brazil Brazil, Sao Paulo Electrosphere Solar activity Atmosphere conductivity Space weather Geomagnetic storms Power transmission failures Solar cycle Atmospheric discharges atmosphere ionosphere networks rupture coupling conductivity solar activity discharge concentration anomalies lead correlation cosmic rays Lightning solar cycles sunspots reduction storms
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Summary:	High-voltage transmission networks represent a large electrical circuit just above the ground subjected to a number of transient overcharges of various kinds, some of which may lead to failures. Some failures might be related to anomalies of the geophysical environment. We have analyzed one unprecedented long series of transmission grid failures (9 years) on high-voltage networks located in São Paulo state, southeastern Brazil, from 1998 to 2006, which includes an important fraction of the past solar activity cycle 23. Ninety-five distinct failure causes were given by the power line operator to explain the transmission grid shut downs. Most failures were attributed to atmospheric discharges, corresponding to 1,957 failures out of a total of 4,572 for the whole period at 138 kV, and 170 out of 763 at 440 kV, respectively. They correspond to less than one ten thousandth of the actual number of atmospheric discharges recorded in the same area, demonstrating the grid’s high resilience to breakdowns due to lightning. A clear concentration of failures in the region’s thunderstorm season has been found. A significant 67 and 77 % reduction in the number of failure rates per year has been found for the 138 and 440 kV grids, respectively, for the period studied, in good correspondence with the decay in the sunspot numbers. No obvious correlation was found between power failures and the planetary index of geomagnetic activity or major geomagnetic storms in the period, either on short or on long time scales. Assuming that the dependence of the electrosphere/ionosphere-ground coupling on the external geophysical environment plays a major role in explaining the reduction in power failures as the solar cycle wanes, it is suggested that the increase in atmosphere conductivity caused by the larger cosmic ray flux then reduces the threshold voltage required to produce lightning strokes, so reducing their effectiveness in disrupting high-voltage power lines.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0169-3298 1573-0956
DOI:	10.1007/s10712-012-9191-1