Does time series analysis confirms the relationship between space weather effects and the failures of electrical grids in South Poland?

Our Sun is not a constant body. Its behavior changes in various scales. Solar activity (SA) is usually characterized by a number of sunspots emerging on the solar surface, varying in time. The 11-year solar cycle (from one minimum to the next minimum epoch of SA) shows temporal changes of the level of SA. The 22-year solar magnetic cycle is associated with the reversal of the Sun’s global magnetic field in the maximum epoch of SA. At the maximum epochs (a period with a peak in the sunspot number), the polarity of the Sun’s global magnetic field reverses, so that the North magnetic pole becomes the South and vice versa. Accordingly, there exists the 22-year solar magnetic cycle. As a consequence, the 22-year solar magnetic cycle consists of two different polarity periods (from one maximum to another maximum epoch of SA), each lasting 11 years. When the global magnetic field lines are directed outward from the northern hemisphere of the Sun and are directed backward to southern hemisphere, this 11 year part of the 22-year solar magnetic cycle called the positive (\(A>0\)) magnetic polarity epoch, while in vice versa case, it is called the negative (\(A<0\)) magnetic polarity epoch [1].

The exceptional phenomenon of the activity of Sun is solar wind- an extension of the outer atmosphere of the Sun (solar corona) into interplanetary space [2], changing in time and having the asymmetrical distribution with the heliolongitudes, especially during the solar minimum. The space around the Sun, where the solar wind dominates, is called the heliosphere.

Sun is also a source of the outstanding solar flares (SFs) and the coronal mass ejections (CMEs) causing the powerful disturbances in the interplanetary space. They appear in time by chance, sporadically, without any regularity, increasing its frequency in the maximum epochs of SA. Consequently, the interplanetary space is fulfilled with the electromagnetic fields consisting of the regular and turbulent components developing dynamically with different time and spatial ranges. Thus, Earth’s environment is affected by the solar-driven effects, commonly known as space weather. The term space weather refers to conditions on the Sun and in its atmosphere, as well as, in the heliosphere that can influence the space born and ground based technological systems [3] and human existence [4].

Variability of the Sun [5], continuously measured from 17th century, influences the Earth in a number of ways, depending on the level of solar activity. Various phenomena occurring on the Sun lead to a transformation of solar magnetic energy into space-weather-driving incidents. During the solar maximum transient phenomena, as above-mentioned solar flares and coronal mass ejections are very frequent, and lead to an increase in the injection, acceleration, and transportation of solar energetic particles (SEPs).

Interactions of Sun-induced-phenomena with the Earth’s magnetic field can lead to a geomagnetic storm. Strong magnetic storm affects the normal operation of ground located electrical systems and causes damages of satellites and its equipment, which impacts satellite phones, GPS systems etc. Geomagnetic storms are classified by the planetary geomagnetic Kp index values. According to the National Oceanic and Atmospheric Administration Space Weather Geomagnetic Storms Scale (http://www.swpc.noaa.gov) when \(Kp=5\), then it is G1 minor geomagnetic storm, for \(Kp=6\), then it is G2 moderate storm, \(Kp=7\): G3 strong, \(Kp=8\): G4 severe, and \(Kp=9\): G5 extreme geomagnetic storm. [6] formulated the following geomagnetic storm criteria: long duration (>3 hours), large and negative \(B_{z}\) HMF component (\(< -10~\mbox{nT}\)) events, linked with interplanetary duskward electric fields \(> 5~\mbox{mV/m}\). They found a one-to-one relationship between these interplanetary events and intense geomagnetic storms, and recommended that these conditions can be used in the geomagnetic storm predictions.

Among the main space weather effects [3] are: radio blackouts, solar radiation storms, and geomagnetic storms. Usually the real space weather event is the mixture of the above mentioned phenomena, with complex temporal and spatial distribution. Radio blackout is caused by SF, when X-ray emission increases low altitude ionization. As a consequence it is observed the absorption and disruption of high frequency (HF) radio waves (3–30 MHz). HF radio blackouts are especially frequent in polar regions. It can affect the proper operation of aviation and shipping, as well as the military systems [7].

Over the past decades many investigators studied the possible effects of extreme space weather phenomena on electricity transmission infrastructure, e.g. [7–9], but non of them concerned Polish energy infrastructure. Particularly, space weather effects may disturb infrastructure, such as transformers, required to operate electricity transmission and announce voltage instabilities that consequently protect the power system assets from damage. Also satellites are unsafe [10], because energetic electrons trapped in the outer radiation belt, causing electrostatic charging and discharging, can damage electronics and solar panels. Fortunately, total destruction is quite rare, because satellites are planned to accept a total dose over some lifetime, with good safety limitations: temporary outages and fleet aging are both more probable [7].

During solar radiation storms SEPs are accelerated by SFs and CMEs. Flux of energetic particles can influence not only technological systems (e.g. the electronic devices on satellites, aircraft, etc.) [11], but also has an impact on the human existence (astronauts, air-crew, and airline passengers) [3].

Geomagnetically induced currents (GIC) are a phenomenon initiated by the interaction between space weather and the Earth’s magnetic field. As a powerful geomagnetic storm penetrates the Earth’s magnetosphere, it can result in a high current electrojet in the ionosphere. The electrojet can reach several million amperes. This current varying with time induces a geoelectric field. The geoelectric field causes a current to flow in the same direction, being recognized as GIC, e.g. [12]. In regions of increased ground resistivity the current will flow through power lines [8, 9], gas pipelines [13, 14] or other available conductive media, such as railways. For gas pipelines, GIC can cause a variation in the pipe to soil voltage which can disturb the cathodic protection system [9]. During the extreme geomagnetic storms, GIC can disrupt transmission systems. Extreme GICs can directly damage transformers through spot heating [3]. The transformer damage can have substantial financial consequences because it can potentially leave areas without power for a long time, as well as incurring the cost of replacing the transformer. In [9] it was shown that high geomagnetic latitudes (greater than 60^∘), where geomagnetic disturbances are more significant and more frequent, are at particular risk from GIC. Although, it has to be underlined that at low and mid-latitude countries GIC can cause the failure of transformers through repeated heating of the transformer insulation [15, 16].

The development of current knowledge about the influence of GIC on power systems was caused mainly based on the analyses of historical events. The most recognized event happened in Canada in the March 1989 storm [17]. At 2:44 a.m. on March 13, 1989 a 100 ton static VAR capacitor at Chibougamau sub-station, Quebec, Canada, tripped and went off-line due to GIC causing a protective relay to sense overload conditions. The tripped VAR capacitor caused a cascade of failures throughout the Quebec power grids; most notably five transmission lines from James Bay were tripped causing a loss of 9450 MW. The total load in the grid at the time was about 21,350 MW. A mere 75 seconds after the first capacitor went down most of the province was left without power. Automatic load reduction systems tried to restore balance in the power system by disconnecting towns and regions but failed. This cascade of spreading failures was much too fast for any meaningful form of manual intervention by operators to take place. 6 million of Hydro-Quebec customers were left without power for up to 9 hours. The total cost of repairs and replacement electricity for the owner Public Service Electric and Gas was later estimated to be above US$20 million [18, 19].

The second well-known event is the Halloween Storm, on October 30, 2003. Two CMEs hit Earth close to each other in time resulting in \(Kp=9\) events with peak geomagnetic Dst index values of −383 nT. The first CME erupted from the Sun at 11:10 (UTC) on the 28th of October 2003 and hit Earth about 19 hours later at roughly 06:10 (UTC). The second CME erupted at 20:49 (UTC) and reached Earth at 16:20 (UTC). At 20:04 (UTC) the storm peaked and the geoelectric field reached values of 2 V/km in the Malmo region [12]. This storm had a wide array of consequences for different technological systems. In Sweden on October 30 21:07 (local time, UTC + 1), a blackout occurred that lasted for 20–50 minutes and affected 50 000 customers in Malmo and surrounding areas. The root cause was a relay in the 130 kV system [12]. The same storm is reported to have caused significant transformer damage in South Africa. Over 15 transformers in South Africa were damaged during this period, some beyond repair [4, 15]. Among other affected systems can be mentioned, the Wide Area Augmentation System (WAAS), a navigation system based on GPS, operated by the Federal Aviation Administration, which was out of service for 30 hours and also the ADEOS-2 satellite that was severely damaged due to the storm [18].

Particularly, it is worth mentioning that on 29th October 2003, at 07:46 an import from Poland to Sweden via SwePol Link of 300 MW energy was disrupted. Similarly, on 20th of November 2013, at 18:04 SwePol Link 400 kV line tripped disrupting an import from Poland of 400 MW [19, 20].

The described above cases of energy infrastructure failures make society aware that geomagnetic storms, and hence GIC, are the results of a very complicated sequence of events, originating from magnetic energy accumulated in the Sun’s interior. This energy is transferred via interplanetary space, the magnetosphere, the ionosphere, the ground to finally end up as a quasi-DC current flowing through transformers in the power systems. Since transformers are generally not designed to handle DC current flowing through the neutral point, this causes problems. The resultant saturation of the transformer core is the source of all primary risks to the power system [19]. Developing and maintaining the national power systems it must be taken into account that geomagnetic storms are very real social treats and have a potential to cause substantial damage both, to the power system and to other critical infrastructures. If not properly handled the socioeconomic consequences can be severe. Thus, it is crucial to analyze applying various mathematical and statistical tools, does and in what extent, the Polish energy infrastructure is affected by the space weather outcomes. Such an analysis is presented in the next sections of this paper. It is worth mentioning that time series analysis tools are often used in the studies of space weather issues [21–25], but for the first time are used to portray connections between the Polish energy infrastructure elements’ failures and geoeffective incidents.

This paper is organized as follows: in Sect. 1 we present a short overview about geomagnetically induced currents and their source. In Sect. 2 we characterise electrical grids in the southern Poland and describe common causes of their failures. Section 3 introduces data analysed in this paper. In Sect. 4 we depict our methods and results, as well as present a discussion of our results. Section 5 contains our conclusions.