Solar activity and transformer failures in the Greek national electric grid

Abstract

Aims: We study both the short term and long term effects of solar activity on the large transformers (150 kV and 400 kV) of the Greek national electric grid. Methods: We use data analysis and various statistical methods and models. Results: Contrary to common belief in PPC Greece, we see that there are considerable both short term (immediate) and long term effects of solar activity onto large transformers in a mid-latitude country like Greece. Our results can be summarised as follows:1. For the short term effects: During 1989-2010 there were 43 ''stormy days'' (namely days with for example Ap ! 100) and we had 19 failures occurring during a stormy day plus or minus 3 days and 51 failures occurring during a stormy day plus or minus 7 days. All these failures can be directly related to Geomagnetically Induced Currents (GICs). Explicit cases are briefly presented. 2. For the long term effects, again for the same period 1989-2010, we have two main results:(i) The annual number of transformer failures seems to follow the solar activity pattern. Yet the maximum number of transformer failures occurs about half a solar cycle after the maximum of solar activity. (ii) There is statistical correlation between solar activity expressed using various newly defined long term solar activity indices and the annual number of transformer failures. These new long term solar activity indices were defined using both local (from the geomagnetic station in Greece) and global (planetary averages) geomagnetic data. Applying both linear and non-linear statistical regression we compute the regression equations and the corresponding coefficients of determination.Key words. geomagnetically induced currents (GIC) -solar activity -technological system -non-linear phenomena -aeronomy Introductory theory -motivationThe primary cause of space weather are explosions in the Sun powered by its strong magnetic field which affect man-made technological infrastructure in space, disturb communications and GPS signals and couple through Geomagnetically Induced Currents (GICs for short) with the large-scale high voltage power grid. The most well-known case of the impact of large-scale space weather events on the electric grid is the 1989 Hydro-Quebec blackout caused by the 13 and 14 March super storm. Highly acclaimed institutions (like the US National Academy of Sciences 2008, the UK Royal Society of Engineering 2013, etc.) have issued extended reports arguing that space weather super storms may cause trillions of dollars of damage although it is acknowledged that these estimates may not be totally accurate. There is general consensus however that space weather super storms constitute a serious threat. The main cause of GICs is the interaction of the geomagnetic field with the magnetic field carried within CMEs and the surrounding background magnetised solar wind that is modulated by them. There are several space weather phenomena which tend to be associated with a geomagnetic storm or are caused by a geomagnetic storm (see Chapman & Ferraro 1930...

Geomagnetically Induced Currents Caused by Interplanetary Shocks With Different Impact Angles and Speeds

“…The blackout following that storm was associated with permanent damage to a transformer located in a New Jersey power plant, in the United States, caused by substorm‐like events leading to a d B /d t peak of approximately ∼480 nT/min. In equatorward regions, GICs are associated with geomagnetic storms and SI + events (Béland & Small, ; Carter et al, ; Fiori et al, ; Kappenman, ; Zhang et al, , ; Zois, ). Zois () showed that the number of reported transformer failures in a period of ∼20 years in midlatitude regions in Greece (35°–41°) was associated with solar activity.…”

“…In equatorward regions, GICs are associated with geomagnetic storms and SI + events (Béland & Small, ; Carter et al, ; Fiori et al, ; Kappenman, ; Zhang et al, , ; Zois, ). Zois () showed that the number of reported transformer failures in a period of ∼20 years in midlatitude regions in Greece (35°–41°) was associated with solar activity. Zhang et al () showed that GIC response to the SI + event preceding the 2015 St. Patrick's Day storm recorded by midlatitude stations along the Chinese coast was larger than those recorded at the same stations during storm main phase.…”

Validating GIC Models With Measurements in Austria: Evaluation of Accuracy and Sensitivity to Input Parameters

“…Most past studies concentrated on GICs in high‐latitude regions (Beggan et al, ; Foss & Boteler, ; Myllys et al, ; Viljanen & Pirjola, ; Viljanen et al, ; Wik et al, ) where the geomagnetic variations, and therefore also the GICs, are larger. Studies of GICs in low‐latitude countries, which in the past have been expected to be of little interest due to their small magnitudes, have become far more numerous in recent years and have been carried out around the world (Barbosa et al, ; Blake et al, ; Divett et al, ; Matandirotya et al, ; Torta et al, ; Watari, ; Zhang et al, ; Zois, ), with results showing that GICs are also relevant in midlatitude and low‐latitude regions.…”

Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach

“…Direct currents in transformer windings can lead to half-cycle saturation of the transformer at levels of tens of amperes (Molinski, 2002). In mild cases, this can lead to reduced AC transmission capability, transformer heating (Price, 2002;Pirjola, R. L. Bailey et al: Modelling geomagnetically induced currents 2002), and possibly a shorter transformer life (Zois, 2013). In the worst case it can lead to transformer fires and complete transformer failure (Gaunt and Coetzee, 2007;Wik et al, 2008).…”

“…Highlatitude countries (in particular those in the auroral zone band of 55-70 • geographic latitude, where the auroral electrojet dominates) and regions of high ground resistivity are most susceptible to GICs , and there have been several studies conducted in these areas (Viljanen and Pirjola, 1994;Beamish et al, 2002;Wik et al, 2008;Myllys et al, 2014). Research into GICs in lowlatitude and equatorial countries such as the Czech Republic (Hejda and Bochníček, 2005), Brazil (da Silva Barbosa et al, 2015), Spain (Torta et al, 2012), Greece (Zois, 2013), Japan (Watari et al, 2009), South Africa (Bernhardi et al, 2008;Matandirotya et al, 2015), Australia (Marshall et al, 2011), and New Zealand (Beland and Small, 2005), which were previously considered to be at low risk from all but the most extreme geomagnetic storms, show that considerable GICs (in the range of tens of amperes) do also appear at lower latitudes. In these regions, large geomagnetic variations have been shown to result from ring current intensification, where solar wind is the driving force (Kappenman, 2005).…”