Session - Geomagnetically Induced Current and Space Weather

E. Clarke, P. Wintoft, A. Viljanen, A. Thomson

A well known ground effect of space weather is that of geomagnetically induced currents (GIC) or geomagnetically induced potential (GIP). These occur during geomagnetic storms and sub-storms and are potentially a hazard to power transmission networks, railway signalling operations and pipeline protection mechanisms. For example, extreme magnetic storms have resulted in widely reported electricity network problems in the past and could do so again in the future.

Whilst it is accepted that increases in the electric field or in the rate of change of the magnetic field are important, questions remain over details of the physical phenomena. For example, how important is the length of period over which magnetic storms, and therefore high rates of change, last? Do single peaks have the most impact? Is the effect of cumulative damage over longer periods with many storms also important and can this damage be monitored and modelled?

This session welcomes contributions on all aspects of GIC, from a solar-terrestrial physics, a geophysical and/or an engineering perspective. Predictions and models of GIC and how they are applied in practice, vulnerability of networks, systems and equipment to GIC and GIP, monitoring of GIC either by proxy or by direct measurement and studies on the risk, where the consequences of GIC are considered, are particularly encouraged.

Talks
Tuesday November 24, 11:00 - 13:00, Mercator

Poster Viewing
Tuesday November 24, 10:00 - 11:00, Poster area

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Talks : Time schedule

Tuesday November 24, 11:00 - 13:00, Mercator

11:00	GIC in the Norwegian Power Grid	Ohnstad, T et al.	Invited Oral
	Trond M. Ohnstad, Evald Saethre, Kaare Rudsar
	Statnett SF
	Statnett is the operator ans owner (TSO) of the Norwegian Power Grid. The transmission system i Norway have voltage levels from 132kV and up to 420kV. The 420kV system covers all of Norway and consists of 10 000km of power lines and about 200 power transformers. The transformers have solid earthed neutral and the system is susceptible to GIC during geomagnetic storms. Since 1999 Statnett have performed measuremnet of GIC in some selected transformer neutrals in the power system. The paper will present results from measurements and registration of GIC. It will describe the influence GIC have to the system voltage, reactive power flow and harmonics. The paper will present a plan for mitigation and other actions to reduce the risk of serious power outages due to GIC.
11:20	GIC events and their impact on Finnish transmission network during geomagnetic storm on 17th and 18th of March 2015	Rauhala, T et al.	Invited Oral
	Tuomas Rauhala[1], Jarmo Elovaara[1], Ari Viljanen[2]
	[1] Fingrid Oyj; [2] Finnish meteorological institute
	The Finnish transmission system owner and operator Fingrid performs continuous monitoring of geomagnetically induced currents (GIC) at the Alajärvi substation in Central Finland (lat 63 N). The monitoring is based on a continuous measurement of current flowing through the neutral point of the 400/220 kV power transformer. The possible GIC events are detected by comparing a pre-defined threshold value against the 10 second average value of the measured current. This presentation covers and summarizes the measurements during the large geomagnetic storm on 17-18 March 2015, when model calculations indicate that GIC in Finland reached values comparable to those during the superstorm on 29-30 October 2003. We provide an overview of the impact of the GIC event on the technical performance of the Finnish transmission network. The technical performance is described by means of the measured current distortion at the Alajärvi substation, changes in the network voltage profile and variations in the reactive power consumption of the power transformers at Alajärvi as well as at nearby 400 kV and 220 kV substations. Although high temporary current levels were recorded at Alajärvi during the event, its impact on the Finnish transmission system remained local and very limited. The key reasons for the limited impact are also discussed in the presentation. Additionally, the current levels recorded on 17-18 March 2015 are reflected against minor and moderate GIC events within the period of 2013-2015.
11:40	Geomagnetic Conditions in Ireland during the St. Patrick’s Day 2015 Storm	Anon, A et al.	Oral
	Seán P. Blake[1], Peter T. Gallagher[1], Alan Jones[2], Colin Hogg[2], Joe McCauley[1], Ciaran Beggan[3], Alan Thomson[3], Gemma Kelly[3], David Bell[4]
	[1] Trinity College Dublin; [2] Dublin Institute for Advanced Studies; [3] British Geological Survey; [4] Eirgrid Plc
	On March 15, 2015, two coronal mass ejections were launched in quick succession from the Sun. Two days later, on March 17 (St. Patrick's Day), they impacted the Earth's magnetosphere, resulting in a geomagnetic storm with a planetary K-index of 8. A local K-index of 7, which was sustained for 9 hours, was derived from magnetic observations at the Rosse Solar-Terrestrial Observatory in the Irish midlands. This was the most geomagnetically disturbed day observed in Ireland in over a decade. This disturbance was also measured across a new network of magnetometers at Valentia, Birr, Leitrim, and Armagh in Northern Ireland. Using these magnetic measurements, electric fields were calculated using both a plane-wave approximation and a thin-sheet surface electric field model supplied by the British Geological Survey. The calculated electric fields were then coupled to a model of the power grid to estimate the geomagnetically induced currents in the power network across the island. Preliminary calculations for the electric field suggest values of greater than 5 V/km during the peak of the storm. These are similar to condition observed in Britian during the Halloween 2003 storms.
11:55	GIC at mid-latitudes under extreme Dst scenarios	Kelly, G et al.	Oral
	Gemma Kelly[1], Ari Viljanen[2], Ciaran Beggan[1] and Alan Thomson[1]
	[1] British Geological Survey, UK; [2] Finnish Meteorological Institute, Finland
	The Dst index is primarily a measure of the magnitude of the equatorial magnetospheric ring current, based on an hourly average of the variation of the Horizontal (H) component from a number of low and mid-latitude ground-based observatories. Extreme values of this index are rare; for example the largest in recent decades occurred during the March 1989 storm, with Dst peaking at -589 nT. Larger values of Dst have been established for the Carrington event – in September 1859 the Bombay observatory recorded a peak of about -850 nT. However, some researchers have suggested that Dst may have been even larger still (-1760 nT), based on one value from Bombay during the 1859 storm. More recent theoretical work has suggested that -2500 nT is the largest possible value physically achievable, given our knowledge of the magnetosphere. Although the ring current variation affects low to mid-latitudes directly, at higher latitudes most variation of H is due to auroral electrojet activity. Motivated by the largest theoretical possible Dst value, we investigate the size of the H variation at high latitudes that might occur during large Dst excursions, by extrapolating relationships observed between H and Dst from previous large storms. To test the consequence of these large H variations we compute the likely GIC in mid-latitude European high-voltage power distribution networks, based on a set of conductivity and grid models of similar complexity, during geomagnetic storms with Dst values of -800, -1700 and -2500 nT.
12:10	Modelling of the natural electromagnetic interference for GIC applications	Trichtchenko, L et al.	Oral
	Larisa Trichtchenko
	NRCan
	The common approach for calculations of GIC in power networks or calculations of pipe-to-soil potential drop for pipeline applications is based on the electrical network approximation and is regarded the network as ohmic resistive network. In this presentations the results of the rigorous first principal modelling of the electromagnetic induction in the long layered structures (cables, pipelines, etc.)will be discussed. The frequency-dependent impedance of the network will be then investigated and simple formulas will be presented. These simple formulas will be compared with the rigorous modelling and will be recommended for use in GIC modelling. These simple expressions of frequency-dependent impedance can be used for the whole range of frequencies and therefore are applicable for high frequency variations in the geomagnetic field. It is especially important for calculations of GIC when there is a concern that frequencies above 1 Hz should be taken into account.
12:25	Nowcasting Ground Magnetic Perturbations with the Space Weather Modeling Framework	Welling, D et al.	Oral
	D. T. Welling[1], G. Toth[1], T. I. Gombosi[1], H. Singer[2], G. Millward[2]
	[1] University of Michigan Center for Space Environment Modeling; [2] NOAA Space Weather Prediction Center
	Real-time monitoring of ground-based magnetic perturbations is a critical step towards predicting geomagnetically induced currents (GICs) in high voltage transmission lines. Currently, the Space Weather Modeling Framework (SWMF), a flexible modeling framework for simulating the multi-scale space environment, is being transitioned from research to operational use (R2O) by NOAA’s Space Weather Prediction Center. Upon completion of this transition, the SWMF will provide localized B/t predictions using real-time L1 observations of the solar wind as input. This presentation describes the operational SWMF setup and summarizes the changes made to the code to enable R2O progress. The framework’s algorithm for calculating ground-based magnetometer observations will be reviewed. Metrics from data-model comparisons will be reviewed to illustrate predictive capabilities. Early data products, such as regional-K index, will be presented. Finally, early successes will be shared, including the code’s ability to reproduce the recent March 2015 St. Patrick’s Day Storm.
12:40	Analysis of the importance of the Earth resistivity and the power network status in modelling geomagnetically induced currents in Spain	Torta, J et al.	Oral
	J. M. Torta[1], S. Marsal[1], A. Marcuello[2], P. Queralt[2], J. Ledo[2]
	[1] Observatori de l’Ebre, (OE) CSIC - Univ. Ramon Llull, Roquetes (Spain); [2] Institut Geomodels. Dept. Geodinàmica i Geofísica. Universitat de Barcelona, Barcelona (Spain)
	Through an assessment of the hazard from geomagnetically induced currents (GIC) to the power network in Spain, we analyze the importance of the Earth resistivity model used to provide estimates of the expected GIC. In the absence of the 2D or 3D specific information, we have employed 1D model calculations, i.e. a series of horizontal layers of different resistivity based on the sparse published MT survey results; on the grounds that assessing the vulnerability of a system usually does not require knowledge of the precise values of predicted GIC. None of the proposed 1D structures performs substantially better than modelling the Earth as a uniform half-space, suggesting that the actual structure must be laterally heterogeneous, especially because the contrast is large at ocean-land interfaces. Though at mid-latitude regions the source field is rather uniform and the effect of its spatial changes might be of less importance, this has also been investigated by interpolating the field from the records of several geomagnetic observatories with the technique of spherical elementary current systems. 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. The switching off of a key transmission line or transformer can be essential to boost significant currents through the remaining elements. In addition, we have performed measurements of the surface impedance in the vicinity of one of the transformers where we have GIC measurements. This allows assessing 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.

Posters

Tuesday November 24, 10:00 - 11:00, Poster area

1	Real-time estimation of geomagnetically induced currents	Viljanen, A et al.	p-Poster
	Ari Viljanen[1], Risto Pirjola[1,2]
	[1] Finnish Meteorological Institute; [2] Natural Resources Canada
	The well-established modelling of geomagnetically induced currents (GIC) in power grids can be easily applied to real-time calculation. Using measurements of the geomagnetic field and a model of the ground conductivity, the geoelectric field can be determined until the latest time-step. Given a model of a power grid, GIC driven by the geoelectric field can then be computed. The real-time mode has some differences compared to analyses of past events. First, real-time magnetometer data need automatic quality checks to remove at least the most evident erroneous values. A simple and powerful method for this is a comparison of the time derivative of the magnetic field between a set of magnetometer stations at each time step. Second, power grids are not static but undergo frequent changes in configuration. We outline how such modifications could be taken into account in real-time.
2	Solar Shield: first principles GIC forecasting using state-of-the-art space science simulations	Pulkkinen, A et al.	p-Poster
	Pulkkinen, A.[1], S. Mahmood[2], C. Ngwira[3,1], C. Balch[4], S. Habib[1], F. Policelli[1], R. Lordan[5], D. Fugate[6], W. Jacobs[6]
	[1] NASA GSFC; [2] DHS S&T; [3] The Catholic University of America; [4] NOAA SWPC; [5] Electric Power Research Institute; [6] Electric Research & Management, Inc.
	A NASA Goddard Space Flight Center (GSFC) Heliophysics Science Division-led team that includes NOAA Space Weather Prediction Center, Electric Power Research Institute (EPRI) and Electric Research and Management, Inc. (ERM) participants has recently partnered with the Department of Homeland Security (DHS) Science & Technology (S&T) to better understand the impact of Geomagnetically Induced Current (GIC) on the electric power industry. NASA GSFC, initially working with EPRI and ERM, developed a Solar Shield system to predict the GICs. The present focus is to extend the Solar Shield system project to enhance the forecast capability (for a description of the "old" system, see http://ccmc.gsfc.nasa.gov/Solar_Shield). We call the new activity as “Solar Storm GIC Forecasting: Solar Shield Extension.” One of the general goals of Solar Shield Extension is to extend the prediction system coverage across CONUS. The team also uses the latest enhancements in space weather modeling capacity to increase the technological readiness level of the system. As a part of the process to enhance system reliability, the team worked to improve understanding of the power industry user requirements with emphasis on improving the forecasting system to better support operational decisions about proactive GIC mitigation actions. The GIC forecasting system requirements were developed and measured against this end goal. In this report, we will discuss the latest Solar Shield activities including end-user requirements development.
3	An Analytical Method for Evaluation of Solar Storm Impact on Power System Operation	Sokolova, O et al.	e-Poster
	Olga Sokolova, Prof. Nikolay Korovkin, Prof. Victor Popov
	Peter the Great St.Petersburg Polytechnic University, Russia
	Solar storms are known to affect critical infrastructure. Industry awareness of solar storm impact varies from sector to sector. Solar storm impacts on power grids are mostly studied, compared to other systems. However, solar storms, as less frequent phenomena, are not yet well understood; especially when the threat is virtual and regions of influence are poorly defined. The interference of geomagnetic disturbance with power grid may lead to one of the following scenario: • Voltage avalanche due to reactive power deficit followed by relay protection miss operation and power system equipment outage; • Voltage avalanche due to reactive power deficit without power system equipment outage; • Power system equipment outage caused by relay protection miss operation without widespread voltage blackout. The primary factor that determines blackout scenario is the value of power loss. Nevertheless, the system’s vulnerability criterion is a combination of technical and naturally predefined factors. The proposed method allows finding optimal or nearly optimal mitigation procedures under given geomagnetic conditions. The optimization function is the minimum power outage. When entering the grid, geomagnetically induced currents (GIC) are distributed over network elements by changing their parameters. For the most of the cases, power system equipment is no barrier to GIC distribution. Thereby, GIC affect all three squads of generation – transmission – distribution chain. Operators should ensure sufficient redundancy of customer’s power supply. GIC are simultaneously distributed over large geographic area. Thereafter, common risk assessment approach using list of normative contingencies cannot assess given risk policy [1]. GIC as a quasi-direct current (f=10^-4 - 10^0 Hz) weakens power system state by affecting equipment operation. Power grid equipment is designed to withstand direct currents in the form of short circuit current. Nevertheless, inrush current is cleared within several periods while GIC may last for hours with random magnitude. The power system equipment robustness to solar storm effects can be determined considering the type of equipment and its design characteristics. Even though power transformers are known to be the most prone power system equipment to GIC, its resiliency to solar storm is highly depended on its construction type. For instance, the 400 kV single-phase core-type transformer is driven to saturation by GIC equal to transformer’s nominal no-load current (in the range of several Ampers). Meanwhile, 400 kV three-phase three-limb transformer can be hardly driven to saturation even by GIC that is 50 times greater than nominal no-load current [2]. In contrary, the least vulnerable power system equipment is the wire used for overhead transmission lines. The value of maximum admissible current over transmission lines is limited by two factors: conductor melting and wire sag. The maximum admissible current for the 400 kV transmission line is in the range of 1-2 kA for the air temperature equal to 0 degree Celsius. The second parameter that specifies power grid robustness against solar storm effects is the system effect of network element loss. Power transformers are not only the most prone to GIC effects power system equipment but also the key element of reliable power system operation. Furthermore, power transformers are characterised by high reparation cost up to USD 20 million and it takes as long as 18 months to replace them. The same statement is true for synchronous machines i.e. another type of prone power system equipment by severe geomagnetic disturbance. The proposed method precedes the whole scale analysis of solar storm impact on power system operation. The analysis is done for the given geomagnetic conditions. The algorithm consists of the following steps: -The first step includes calculation of GIC distribution in the studied grid using voltage node method [3, 4]. -The second step refers to contingency analysis. The calculated GIC levels in the grid’s nodes are correlated with installed equipment characteristics. -The third step is the relay protection algorithms efficiency verification caused by instrument transformer failure to operate. -The forth step is the small-signal stability analysis by reactive power margin calculation. -The fifth step is the topology analysis. The study of dependence between topology change and GIC risk level. The typical power system states are investigated e.g. at winter and summer maximum and minimum load. Even though power system is characterised by enormous number of states, the emergency control algorithms are verified for typical power system states including normative maintenance states. -The sixth step is the mitigation action analysis and their correction. -The seventh step is the coordination of proposed mitigation action set with power supply requirements put by utilities. Authors suggest that proposed algorithm is a useful tool for pre-fault analysis of power system fault scenario caused by geomagnetic disturbance. REFERENCES: [1] UCTE (2004) Operation handbook final v. 2.5 E, 24.06.2004, Avaliable http://www.ucte.org [2] Sokolova, O., P. Burgherr, W. Collenberg (2014) Solar Storm Impact on Critical Infrastructure, Safety and Reliability Methododlogy and Applications, Proceedings of the European Safety and Reliability Conference (ESREL) 14-18 September 2014, Wroclaw, Poland [3] Pirjola, R., K. Kauristie, H. Lappalainen, A. Viljanen, and A. Pulkkinen (2005), Space weather risk, Space Weather, 3, S02A02, doi:10.1029/2004SW000112 [4] Demirchan, K., L. Neiman, N. Korovkin (2009) Theoretical basics of Electrical Engineering, vol. 1, 2009
4	An analysis of mid-latitude magnetic perturbations during geomagnetic storms	Morley, S et al.	e-Poster
	Morley, Steven; Woodroffe, Jesse; Cowee, Misa; Henderson, Michael; Jordanova, Vania
	Los Alamos National Laboratory
	Using more than two decades of Northern hemisphere magnetometer data, covering the region between 40$^{\circ}$ and 60$^{\circ}$, we have examined the spatial variations of the perturbation magnetic field ($\Delta$B) and its time derivative (dB/dt). Relationships between peak $\Delta$B and peak dB/dt are explored, as are relationships with the strength (measured by the Dst index) of the geomagnetic storm. How these results might affect current operational hazard assessment will be discussed.
5	Developing an Aurora Detection System and Educational Resources for Space Weather using a Raspberry Pi Magnetometer	Bingham, S et al.	p-Poster
	Ben Grimsdell [1], Liam Crossling [1], Sam Jones [1], George Keyworth-Wright [1], Sophie Gossage [1], Sharon Strawbridge [1], Ciaran Beggan [2], Steve Marple [3], Iain Grant [4], Suzy Bingham [5]
	[1] University of Exeter, [2] British Geological Survey, [3] Lancaster University, [4] Norman Lockyer Observatory, [5] Met Office
	The aim of this project is to create a low-cost magnetometer and to combine it with a cloud detector to produce an auroral detection system for use across the UK. To measure the variation of the external magnetic field, we will combine both a Raspsberry Pi computer and a 3-axis fluxgate magnetometer, constructed by ourselves, based on designs from the British Geological Survey and Lancaster University, which will be set up at the Norman Lockyer Observatory in southern England. Our magnetic field measurements will be analysed along with other data collected by the AuroraWatch Network run by Lancaster University. We will link the cloud detector to the Raspberry Pi to provide additional information about when the aurora might be visible. Eventually we hope to provide software to help visualise the magnetic field measurements so that data can be uploaded & viewed on the Weather Observing Website (WOW) run by the Met Office. In this project we also aim to help educate Key Stage 4 students in the use of magnetometers and provide them with the necessary resources to construct their own instrument. As a result, we hope to raise awareness of the effects of space weather on ground-based systems, such as geomagnetically induced currents in the high-voltage power network. The data collected at various schools across the UK can be uploaded to the AuroraWatch Network and could be added to the WOW database, thus providing information about the longitudinal variance in magnetic field and complementing the fixed observatory network.