D. H. Boteler

A Test Case for the Calculation of Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) in power systems can be attributed to problems ranging from transformer overheating, misoperation of protective relays, and voltage instability. The assessment of the geomagnetic hazard to power systems requires accurate modeling of the GICs that are expected to occur. However, to date, there are no publicly available test cases to validate software programs used to compute GIC. The following paper presents a hypothetical network that can be used as a test case for validating results from GIC modeling software. The network contains many features found in real networks such as: different voltage levels, two- and three-winding transformers and autotransformers, multiple transmission lines in the same corridorn and GIC blocking devices. GIC is calculated in the network for two geoelectric field scenarios: a 1 V/km uniform Northward electric field and a 1 V/km uniform Eastward electric field. Detailed simulation results and corresponding input data are provided for each of the two scenarios. Simulation results that are provided have been validated using four independent GIC modeling programs.

Assessment of GIC risk due to geomagnetic sudden commencements and identification of the current systems responsible

During periods of enhanced geomagnetic activity, geomagnetically induced currents (GIC) flow in power systems potentially causing damage to system components or failure of the system. The largest GIC are produced when there are large rates of change of the geomagnetic field (dB/dt). It is well established that the main phase of a geomagnetic storm, particularly the magnetic substorms occurring during that period, is a cause of large GIC and hence a risk factor for power systems. However, some power system disturbances have been associated with the occurrence of a storm sudden commencement (SSC) prior to the main phase. We investigate the magnetic signature observed on the ground and the associated solar wind and interplanetary magnetic field (IMF) conditions for both SSC and sudden impulse (SI) events, which are grouped together as sudden commencements (SC). SCs are primarily attributed to a sudden enhancement of the magnetopause current. For some events, we show that there is a high-latitude enhancement (HLE) of the SC amplitude and corresponding dB/dt. The limited spatial extent suggests an ionospheric current source. Examination of the polarity of the change in the X-component magnetic field shows that the HLE is due to a sudden increase of the ionospheric convection electrojets. The occurrence of the HLE is more prevalent for SSC-type SCs, SCs caused by coronal mass ejections as opposed to corotating interaction regions, and SCs associated with a large solar wind speed (vsw) prior to the SC or a large Δvsw at the time of the SC.

Simulation of Geomagnetically Induced Currents With Piecewise Layered-Earth Models

The relationship between the changes in the earths magnetic field and the induced geoelectric field during a geomagnetic storm is a frequency-dependent transfer function that depends on earth resistivity at different depths. Taking into account geological variations over the route of transmission circuits has a significant influence on the induced geoelectric fields as well as on the distribution of geomagnetically induced current (GIC) over a geographically large network. This paper summarizes and compares the results of time-domain and steady-state GIC simulations using laterally uniform and piecewise layered-earth models.

Effects of System Characteristics on Geomagnetically Induced Currents

The geomagnetically induced currents (GICs) produced in power systems during magnetic storms are a function of the electric-field amplitude and direction, and the characteristics of the power system. This paper examines the influence of a number of power system characteristics, which include the resistances and structures of the conductors; the length of the transmission lines; the number, type, and resistances of transformers, the substation grounding resistances, and the topology of the network. It is shown that GIC grows with increasing line length but approaches an asymptotic constant value, and a more relevant parameter than the individual line length is the length of the entire system. This paper also derives the effective GIC for a conventional transformer and an autotransformer, and analyzes the behavior of GIC when the network topology changes illustrated with the GIC-Benchmark Model. The results of these studies provide a guide to estimating GIC impacts on a power network.

Geomagnetically induced currents: science, engineering, and applications readiness

This paper is the primary deliverable of the very first NASA Living With a Star Institute Working Group, Geomagnetically Induced Currents (GIC) Working Group. The paper provides a broad overview of the current status and future challenges pertaining to the science, engineering, and applications of the GIC problem. Science is understood here as the basic space and Earth sciences research that allows improved understanding and physics-based modeling of the physical processes behind GIC. Engineering, in turn, is understood here as the “impact” aspect of GIC. Applications are understood as the models, tools, and activities that can provide actionable information to entities such as power systems operators for mitigating the effects of GIC and government agencies for managing any potential consequences from GIC impact to critical infrastructure. Applications can be considered the ultimate goal of our GIC work. In assessing the status of the field, we quantify the readiness of various applications in the mitigation context. We use the Applications Readiness Level (ARL) concept to carry out the quantification.

Modeling geomagnetically induced currents

Understanding the geomagnetic hazard to power systems requires the ability to model the geomagnetically induced currents (GIC) produced in a power network. This paper presents the developments in GIC modeling starting with an examination of fundamental questions about where the driving force for GIC is located. Then we outline the two main network modeling approaches that are mathematically equivalent and show an example for a simple circuit. Accurate modeling of the GIC produced during real space weather events requires including the appropriate system characteristics, magnetic source fields, and Earth conductivity structure. It is shown how multiple voltage levels can be included in GIC modeling and how the network configuration affects the GIC values. Magnetic source fields can be included by using “plane wave” or line current models or by using geomagnetic observatory data with an appropriate interpolation scheme. Earth conductivity structure can be represented by 1-D, 2-D, or 3-D models that are used to calculate the transfer function between electric and magnetic fields at the Earths surface. For 2-D and 3-D structures this will involve a tensor impedance function and electric fields that are not necessarily orthogonal to the magnetic field variations. It is now technically possible to include all these features in the modeling of GIC, and various software implementations are being developed to make these features more accessible for use in risk studies.

Response of Power Systems to the Temporal Characteristics of Geomagnetic Storms

Power lines are exposed to low frequency electromagnetic fields produced by natural (geomagnetic disturbance) sources. The resulting geomagnetically induced currents (GIC) produce excessive harmonics, which affect power system operations. The analysis presented makes extensive use of GIC data from different measuring sites in North American power grids and of geomagnetic data from different geomagnetic observatories. At low temporal resolution hourly GIC index shows good correlation with hourly geomagnetic index provided there is close proximity of the recorded sites. For higher resolution (one minute) the difference between time variations in GIC and geomagnetic field is significant. Although it has been widely popular to use time derivative of geomagnetic field as a characteristic of GIC, we show that ground conductivity is a critical parameter that needs to be included. This is especially important for sharp changes in geomagnetic field, for example, during the beginning of a geomagnetic storm (storm sudden commencement)

Calculation of Induced Electric Field During a Geomagnetic Storm Using Recursive Convolution

The relationship between the changes in the earths magnetic field and the induced geoelectric field during a geomagnetic disturbance is a frequency-dependent transfer function that depends on earth resistivity at different depths. Traditionally, this function is calculated in the frequency domain expressed as an impulse function in the time domain using fast Fourier transform (FFT) and convolved with dB/dt in the time domain to estimate the geoelectric field E. This paper proposes the approximation of the transfer function in the frequency domain using rational functions and to carry out the calculation of E from dB/dt using fast recursive convolution methods.

Response of ionospheric convection to sharp southward IMF turnings inferred from magnetometer and radar data

[1] Reconfiguration of the convection pattern associated with a sudden transition in the north/south component of the IMF from stable positive to stable negative values is investigated for two events using both magnetometer and SuperDARN data. The IMF transition impinges upon the magnetosphere near the 10 MLT sector; perturbations are clearly seen on the dayside at the time of onset and on the nightside with a 10 min delay from onset. This implies a dayside-to-nightside progression of the ionospheric response observed in the magnetic perturbations and SuperDARN velocities, contrary to the globally simultaneous response reported in the literature for a number of other events. The foci of the dawnside convection cells are shown to shift from near midnight toward the dayside, reaching a final location between 06 MLT and 08 MLT within 14–18 min of onset. The location of the duskside convection cell remains in the early afternoon sector both prior to and after the transition for both events. Once the convection foci reach a final location, the overall convection pattern enhances. Citation: Fiori, R. A. D., D. H. Boteler, and A. V. Koustov (2012), Response of ionospheric convection to sharp southward IMF turnings inferred from magnetometer and radar data, J. Geophys. Res., 117, A09302, doi:10.1029/2012JA017755.

Assessment of extreme values in geomagnetic and geoelectric field variations for Canada

Disturbances of the geomagnetic field produced by space weather events can have an impact on power systems and other critical infrastructure. To mitigate these risks it is important to determine the extreme values of geomagnetic activity that can occur. More than 40 years of 1 min magnetic data recorded at 13 Canadian geomagnetic observatories have been analyzed to evaluate extreme levels in geomagnetic and geoelectric activities in different locations of Canada. The hourly ranges of geomagnetic field variations and hourly maximum in rate of change of the magnetic variations have been used as measures of geomagnetic activity. Geoelectric activity is estimated by the hourly peak amplitude of the geoelectric fields calculated with the use of Earth resistivity models specified for different locations in Canada. A generalized extreme value distribution was applied to geomagnetic and geoelectric indices to evaluate extreme geomagnetic and geoelectric disturbances, which could happen once per 50 and once per 100 years with 99% confidence interval. Influence of geomagnetic latitude and Earth resistivity models on the results for the extreme geomagnetic and geoelectric activity is discussed. The extreme values provide criteria for assessing the vulnerability of power systems and other technology to geomagnetic activity for design or mitigation purposes.