Modeling geomagnetically induced currents

Boteler, D. H.; Pirjola, Risto

doi:10.1002/2016sw001499

Cited by 125 publications

(131 citation statements)

References 63 publications

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“…Within a substation the GIC through each transformer, I trans , is calculated by two simple applications of Ohms law, as described by Boteler and Pirjola (). First, we calculate the node voltage, relative to the local substation Earth, by

\overset{V_{e}}{true} = \overset{I_{sub}}{true} \cdot \overset{R_{e}}{true}

as an element‐wise multiplication of the vectors of GIC flowing to Earth,

I_{sub}^{n}

through the EGR at each of the nodes, R e , including the virtual resistors.…”

Section: Method: Developing a Transformer‐level Gic Network Representmentioning

confidence: 99%

Transformer‐Level Modeling of Geomagnetically Induced Currents in New Zealand's South Island

et al. 2018

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During space weather events, geomagnetically induced currents (GICs) can be induced in high‐voltage transmission networks, damaging individual transformers within substations. A common approach to modeling a transmission network has been to assume that every substation can be represented by a single resistance to Earth. We have extended that model by building a transformer‐level network representation of New Zealand's South Island transmission network. We represent every transformer winding at each earthed substation in the network by its known direct current resistance. Using this network representation significantly changes the GIC hazard assessment, compared to assessments based on the earlier assumption. Further, we have calculated the GIC flowing through a single phase of every individual transformer winding in the network. These transformer‐level GIC calculations show variation in GICs between transformers within a substation due to transformer characteristics and connections. The transformer‐level GIC calculations alter the hazard assessment by up to an order of magnitude in some places. In most cases the calculated GIC variations match measured variations in GIC flowing through the same transformers. This comparison with an extensive set of observations demonstrates the importance of transformer‐level GIC calculations in models used for hazard assessment.

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\overset{V_{e}}{true} = \overset{I_{sub}}{true} \cdot \overset{R_{e}}{true}

as an element‐wise multiplication of the vectors of GIC flowing to Earth,

I_{sub}^{n}

through the EGR at each of the nodes, R e , including the virtual resistors.…”

Section: Method: Developing a Transformer‐level Gic Network Representmentioning

confidence: 99%

Transformer‐Level Modeling of Geomagnetically Induced Currents in New Zealand's South Island

et al. 2018

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“…These transformer properties only depend on the geometry and resistances of the network when considering that the horizontal electric field is uniform, meaning that

\overset{a}{true}

can be taken as a network constant for each transformer [ Lehtinen and Pirjola , ; Pirjola and Lehtinen , ]. The vector

\overset{a}{true}

gives the direction of electric field producing the maximum values of GIC, while its modulus provides the proportionality factor to obtain the maximum values of GIC for a specified electric field amplitude [ Torta et al ., ; Boteler and Pirjola , ].…”

Section: Experimental Designmentioning

confidence: 99%

Improving the modeling of geomagnetically induced currents in Spain

et al. 2017

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Vulnerability assessments of the risk posed by geomagnetically induced currents (GICs) to power transmission grids benefit from accurate knowledge of the geomagnetic field variations at each node of the grid, the Earth's geoelectrical structures beneath them, and the topology and relative resistances of the grid elements in the precise instant of a storm. The results of previous analyses on the threat posed by GICs to the Spanish 400 kV grid are improved in this study by resorting to different strategies to progress in the three aspects identified above. First, although at midlatitude regions the source fields are rather uniform, we have investigated the effect of their spatial changes by interpolating the field from the records of several close observatories with different techniques. Second, we have performed a magnetotelluric (MT) sounding in the vicinity of one of the transformers where GICs are measured to determine the geoelectrical structure of the Earth, and we have identified the importance of estimating the MT impedance tensor when predicting GIC, especially where the effect of lateral heterogeneities is important. Finally, a sensitivity analysis to network changes has allowed us to assess the reliability of both the information about the network topology and resistances, and the assumptions made when all the details or the network status are not available. In our case, the most essential issue to improve the coincidence between model predictions and actual observations came from the use of realistic geoelectric information involving local MT measurements.

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“…This constant and imminent threat has led to regulatory actions not only in the United States but also at an international level (see, e.g., Cassak et al, ; Jonas & McCarron, ; Knipp, ; Pulkkinen et al, ). GICs are also a very common subject for modeling studies whose goal corresponds to the improvement of GIC forecasting (Barbosa et al, , ; Blake et al, ; Boteler & Pirjola, ; Ngwira et al, ; Pulkkinen, ; Torta et al, ; Zhang et al, , ).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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The occurrence of geomagnetically induced currents (GICs) poses serious threats to modern technological infrastructure. Large GICs result from sharp variations of the geomagnetic field (dB/dt) caused by changes of large‐scale magnetospheric and ionospheric currents. Intense dB/dt perturbations are known to occur often in high‐latitude regions as a result of storm time substorms. Magnetospheric compressions usually caused by interplanetary shocks increase the magnetopause current leading to dB/dt perturbations more evident in midlatitude to low‐latitude regions, while they increase the equatorial electrojet current leading to dB/dt perturbations in dayside equatorial regions. We investigate the effects of shock impact angles and speeds on the subsequent dB/dt perturbations with a database of 547 shocks observed at the L1 point. By adopting the threshold of dB/dt = 100 nT/min, identified as a risk factor to power systems, we find that dB/dt generally surpasses this threshold when following impacts of high‐speed and nearly frontal shocks in dayside high‐latitude locations. The same trend occurs at lower latitudes and for all nightside events but with fewer high‐risk events. Particularly, we found nine events in equatorial locations with dB/dt > 100 nT/min. All events were caused by high‐speed and nearly frontal shock impacts and were observed by stations located around noon local time. These high‐risk perturbations were caused by sudden strong and symmetric magnetospheric compressions, more effectively intensifying the equatorial electrojet current, leading to sharp dB/dt perturbations. We suggest that these results may provide insights for GIC forecasting aiming at preventing degradation of power systems due to GICs.

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Modeling geomagnetically induced currents

Cited by 125 publications

References 63 publications

Transformer‐Level Modeling of Geomagnetically Induced Currents in New Zealand's South Island

Transformer‐Level Modeling of Geomagnetically Induced Currents in New Zealand's South Island

Improving the modeling of geomagnetically induced currents in Spain

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

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