Why utilities respect geomagnetically induced currents

Geomagnetically induced currents in an electric power transmission system at low latitudes in Brazil: A case study. During large geomagnetic storms, GICs flow between the grounding points of power transformers … Expand.

View 1 excerpt, cites background. Geomagnetically Induced Currents in electric power transmission networks at different latitudes. At the Earth's surface, space … Expand. Geoelectric fields induced in the Earth during geomagnetic storms drive electric currents through the windings of power transformers and the transmission lines carrying electric power. These … Expand. Ground Effects of Space Weather. Assessing the hazard from geomagnetically induced currents to the entire high-voltage power network in Spain.

After the good results obtained from an assessment of geomagnetically induced currents GICs in a relatively small subset of the Spanish power transmission network, we now present the first attempt … Expand. Disastrous space weather risk on large-scale power grid. Geomagnetically induced currents GIC flowing in technological networks at the Earth's surface are ground effects of space weather. During geomagnetic storms, such currents cause bias fluxes in … Expand. Study of effects of changes of earthing resistances on geomagnetically induced currents in an electric power transmission system.

Power grids, which are discretely-earthed networks, constitute an … Expand. View 1 excerpt. Geomagnetically induced currents in Uruguay: Sensitivity to modelling parameters. Abstract According to the traditional wisdom, geomagnetically induced currents GIC should occur rarely at mid-to-low latitudes, but in the last decades a growing number of reports have addressed … Expand.

The effects of geomagnetic disturbances on electrical systems at the earth's surface. Abstract Geomagnetic disturbances have affected electrical systems on the ground for over years. The first effects were noted on the early telegraph in the s and in this century magnetic … Expand. A study of geoelectromagnetic disturbances in Quebec. General results.

With the aim to better understand the flow of geomagnetically induced currents in power systems and to be able to prevent GIC inconveniences in the future, Hydro Quebec Canada carried out … Expand. Geomagnetic disturbance effects on power systems. In the northern hemisphere, the aurora borealis is visual evidence of simultaneous fluctuations in the earth's magnetic field geomagnetic field. These geomagnetic disturbances GMD's , or … Expand.

Nature of the geoelectric field associated with GIC in long conductors such as power systems, pipelines, and phone cables. It is shown … Expand. The effects of GIC on protective relaying. This paper summarizes research and operating experience related to the effects of geomagnetically induced currents GIC on protective relaying.

It shows that if the GIC causes high levels of … Expand. The predictions made by Thomson et al. This value was used to obtain an approximate size of the GIC magnitudes that would flow in each of the transformers of the grid in the event that the extreme value actually occurred during the return period of years at the Ebre Observatory, and we assumed an impulsive event at a cadence of 1 min along the geomagnetic North Figure 9.

As indicated by Torta et al. Maximum values of GICs in each transformer as a consequence of an extreme geomagnetic storm. They correspond to a scenario for a return period of years. Here, we assume an impulsive event along the geomagnetic North.

Although it is a common practice to treat the highest-voltage system as the first approximation, as we did in this study, the correcting terms needed to match the actual flowing currents in the interconnecting transformers will not be attainable until we get the necessary data associated with the lower-voltage systems.

To illustrate the amount of error that can be expected by the omission of low-voltage circuits of the network, we used data from a test case that was released to validate the programs and procedures used by the scientific and technical community to model the GICs Horton et al.

Such a benchmark network contains many features found in real networks, such as different voltage levels, two- and three-winding transformers, autotransformers, multiple transmission lines in the same bus, and GIC-blocking devices see Figure 10 for simplified expressions of the different resistance structures of transformers.

It represents a hypothetical 20 bus network with 8 substations, including 15 transmission lines and transformers of and kV. To model the GICs, Horton et al. They also provide geographical positions of the substations from which one can calculate distances between them in kilometers.

Resistance structures. Resistance structures of top two-winding transformers, middle three-winding transformers, and bottom autotransformers connected to three-phase high-voltage HV and low-voltage LV and LV' transmission lines at the substations. It was found that we could obtain the same results with our programs.

Similarly, for full-wound transformers with a Y configuration and grounded both at high- and low-voltage sides, we used an equivalent circuit with two virtual nodes, one in each side of the transformer. Here, again, the virtual nodes have infinite resistances to ground and the virtual line resistances have been set between the virtual and real nodes equal to the real resistances of the transformer windings.

Meanwhile, the actual transformer winding resistance was set to zero because it was located at the neutral point of the full-wound transformer. We performed test calculations by omitting the entire low-voltage circuit kV in that case. The results for the GICs flowing to ground at each substation are shown in the two central columns after the column of names in Table 2 , whereas those flowing in the phases of each of the transformer windings are shown in the same columns of Table 3.

In both tables, the values obtained by Horton et al. It is both clear and logical that the largest differences were obtained in substations that share lines of high and low voltage. The corrections of calculated GICs in the Spanish kV network that are needed to account for the effects of neglecting the lower-voltage systems might be different. In any case, this test highlights the importance of having all the information concerning the positions and resistances of the network and the substation configurations, both for the high-voltage circuits and for the low-voltage ones, especially if there is galvanic connection between them.

The best way to evaluate the performance of a model such as the one described here is to compare its predictions at a particular transformer neutral point with actual GIC measurements. This, although planned, is still not possible at key sites such as the transformer at the Manzanares substation.

The only measurements coincident with relevant geomagnetic storms were those obtained in to on behalf of our previous project Torta et al. We do compare here the real observations with the predictions of our new model, including the entire kV Spanish network, for the same transformer named TRP1 which was wrongly named as TR2 in Torta et al.

Fortunately, there are no autotransformers in this substation, so it is not galvanically interconnected with low-voltage systems and thus we do not expect major errors by ignoring the or kV networks at farther kV stations Pirjola and Viljanen ; Viljanen and Pirjola ; Pirjola , In Figure 11 , we show the performance of our model as a function of the Earth conductivity structure that we used.

For the latter, we chose either the electrical resistivity model given by Pous et al. In Table 4 , we give the linear correlation coefficients for each case, but in our opinion, this measure is not always the best indicator for quantifying the goodness of such model performances.

This is because models that provide the same signal but are amplified several times will provide the same correlation coefficients. Thus, to evaluate how well the model fits the GIC observations, we define the performance P parameter as. Here, the. Given that the quotient in Equation 10 is a positively defined quantity, P cannot be greater than 1, which is reached when the residuals are zero, i. P would be 0, for example, for a flat model output equal to the mean of the observations.

A negative value of P usually though not necessarily denotes anti-correlation. So, in summary, models that perform better have higher values of P , and one can think of P with some reservations as the fraction of the standard deviation of the observations that can be explained by the model. Results for this parameter are also given in Table 4 for each of the conductivity case structures tested.

None of the proposed 1-D conductivity structures performed substantially better than the homogenous Earth approach, which suggests, as expected, that the actual structure must be laterally heterogeneous, especially because the lateral conductivity contrast is large at ocean-land interfaces Beggan et al. They correspond to the event on 24 to 25 October The measured GIC is in red.

The results are from analyses that used either a uniform ground conductivity set to 0. Since the calculated GIC at one site is slightly sensitive to changes made at distant points of the network Pirjola , our results can be reasonably compared with those presented in Figure 6 by Torta et al.

It is well known that the load and operating procedure of the grid change over time. This explains why the predictions of Torta et al. However, although the overall amplitudes of the present study agree with more realistic conductivity values, our present results correlate worse with the measures of Torta et al.

There are two explanations for this. The first one lies in the fact that Torta et al. This converted the data into a surprising result because one would expect that the spectral method or the time-domain method with a sufficiently high M should give a better fit for the GIC data in this study, we used values of M around min, which yielded results similar to the spectral method.

This, in combination with the Earth model that is perhaps not exactly correct, happened to lead to a good fit with measured GIC data R. Pirjola, D. Boteler, personal communication.

A second explanation is related to the topology of the grid in the vicinity of the measuring substation. There is no doubt that space weather effects are an emerging natural hazard, which can have incredibly important effects on our lives, which are marked by increasing levels of technological dependence. They are in the category of high-impact, low-frequency event risks.

When space weather effects refer to induced currents in technological systems such as power transmission grids, they are called geomagnetically induced currents, or simply, GICs. Modeling efforts require a determination of the electric field occurring in connection with a magnetic storm at the Earth's surface. There are several possible ways to accomplish this task. Once the geoelectric field is obtained, one can calculate the resulting GIC in the conductor system after obtaining a dc model of it.

This engineering task requires knowledge of the geometrical configuration of the network stations and their connections, and also the resistance values of the whole system. This paper provides much useful information about the expected GIC values in the entire Spanish kV power transmission network, which enables us to conduct an assessment of the vulnerability from that hazard. The network contains substations, to which we added 8 substations from France, Portugal, and Morocco across the respective borders.

This represents a complex circuit with transformers and transmission lines. After obtaining the electrical network model to evaluate the maximum expected GIC in each transformer as a result of extreme geomagnetic storms, we developed a post-event analysis from the geomagnetic data obtained at the Ebre Observatory during certain storms, such as the Halloween storm in We also analyzed other episodes coincident with very abrupt sudden storm commencements, as they have proven to be even more dangerous in mid-latitudes.

We found, as expected, that the most susceptible substations to GICs are those in corners or edges of the network. A typical case is that of the Manzanares station which, by having a single transformer, makes it particularly vulnerable. Had the storm of 24 March occurred with the current network configuration and with all the elements operative, GICs would exceed A in the neutral point of the transformer.

However, this extreme value will surely be significantly reduced when transmission lines that are under construction join Manzanares with another station to the east and become operational.

Assessing the vulnerability of a system to GIC hazards usually does not require knowledge of the precise values of expected GICs, instead rough magnitude estimates are sufficient Pirjola a. However, substantial improvements in our enterprise could be attained with further insights. A clear source of uncertainty in the obtained results arises from the fact of having completely ignored the low-voltage circuits that are galvanically connected to the kV system through autotransformers.

This was done because we had neither information on the kV network nor the separate value of the common and series winding resistances of these autotransformers. The kV grid obviously does not have a very big effect on the GIC in the kV system since the lower the voltage, the higher the transmission line resistances, which makes the GICs smaller. The importance of the omission of the low-voltage network has been demonstrated through a test under a GIC benchmark network that has been recently developed by Horton et al.

To test the model performance on a substation close to the location of Ebre Observatory, where the geomagnetic data came from, a homogenous Earth and a couple of 1-D Earth conductivity models have been employed based on the sparse results of magnetotelluric surveys published in the geophysical literature. This could give rise to calculated geoelectric field amplitudes that may be scaled to incorrect values due to the lack of precise ground conductivity data.

In the few sites in which GICs have been or will be effectively measured, the two geoelectric components should be given the correct relative weight when the calculated values are fitted to the measured GIC data Pirjola ; Torta et al.

Therefore, another improvement would be expected after realistically modeling the induced electric field on the surface of the Earth by using a 3-D model of Earth's conductivity, and this can be done in the manner of recent works such as those by Beggan et al. In particular, Spain is located on a peninsula, so a precise estimation of the geoelectric field would benefit from modeling the effects of non-uniform conductivities produced by the coast Gilbert ; Thomson et al.

A critical fact, nevertheless, is the difficulty of obtaining detailed network parameters in the precise instant of a geomagnetic storm and determining the topology of the network for a given amplitude of the incident field.

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Finally, we wish to acknowledge Risto Pirjola and an anonymous reviewer for their valuable comments and constructive criticisms that greatly enhanced the quality of the manuscript. You can also search for this author in PubMed Google Scholar. Correspondence to Joan Miquel Torta. JMT carried out the analyses of the different modeling approaches and the pretreatment of all the geomagnetic and power grid data, obtained both the model results and the comparison with GIC measurements, and drafted the manuscript.

SM designed the performance parameter to evaluate the model performances and participated in the comparison with GIC measurements. He also contributed to the design of the software codes. MQ provided all the information about the positions of each substation and links, the resistances of the lines and substations, and the different transformer configurations at each substation.

She also attended to all questions concerning the engineering aspects of the paper. All authors read and approved the final manuscript.

Reprints and Permissions. Torta, J. Assessing the hazard from geomagnetically induced currents to the entire high-voltage power network in Spain.

Earth Planet Sp 66, 87 Download citation. Received : 28 January Accepted : 16 July Published : 04 August Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Skip to main content. Search all SpringerOpen articles Search. Download PDF. Abstract After the good results obtained from an assessment of geomagnetically induced currents GICs in a relatively small subset of the Spanish power transmission network, we now present the first attempt to assess vulnerability across the entire Spanish system.

Background Solar-terrestrial physics is a discipline with a long tradition, and many observatories and research groups have been dedicated to this subject for a long time.