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1. Modeling geomagnetic induction in submarine cables

   https://doi.org/10.3389/fphy.2022.1022475  

   Chakraborty, Shibaji; Boteler, David H.; Shi, Xueling; Murphy, Benjamin S.; Hartinger, Michael D.; Wang, Xuan; Lucas, Greg; Baker, Joseph B. (October 2022, Frontiers in Physics)

   Submarine cables have become a vital component of modern infrastructure, but past submarine cable natural hazard studies have mostly focused on potential cable damage from landslides and tsunamis. A handful of studies examine the possibility of space weather effects in submarine cables. The main purpose of this study is to develop a computational model, using Python , of geomagnetic induction on submarine cables. The model is used to estimate the induced voltage in the submarine cables in response to geomagnetic disturbances. It also utilizes newly acquired knowledge from magnetotelluric studies and associated investigations of geomagnetically induced currents in power systems. We describe the Python-based software, its working principle, inputs/outputs based on synthetic geomagnetic field data, and compare its operational capabilities against analytical solutions. We present the results for different model inputs, and find: 1) the seawater layer acts as a shield in the induction process: the greater the ocean depth, the smaller the seafloor geoelectric field; and 2) the model is sensitive to the Ocean-Earth layered conductivity structure. 

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2. The Magnetotelluric Method and Its Application to Understanding Geomagnetically Induced Currents

   Schultz, A; Murphy, S; Cotilla-Sanchez, E; Imamura, N; Mate, A; Barnes, A (December 2019, American Geophysical Union, Fall Meeting 2019, abstract #IN41B-16)

   By fusing data obtained from finely spaced continental-scale, magnetotelluric (MT) measurements used for geophysical imaging of the electrical conductivity variations of the Earth's crust and mantle, real-time data of the geomagnetic field variations at a sparse network of fixed geomagnetic observatory and variometer stations, power transmission system sensor data such as neutral ground return current, synchrophasor and other sensor data, information on power grid topology and state, and by applying algorithms we have developed to project the real-time stream of magnetic observatory and variometer data through the frequency-dependent tensor impedances derived from the MT data at each temporary station, we calculate the anomalous voltages on power transmission substations induced by geomagnetically induced currents. Our solution accounts for the first-order impacts on the induced voltages that are due to the effects of 3-D variations in ground (Earth's crust and upper mantle) electrical conductivity structure. These effects when convolved with the path integral of the induced vector ground electric field along the transmission lines are the dominant term in determining the intensity of the geomagnetically induced currents in the system; considerably more so than geomagnetic latitude scaling effects. We discuss integration of real-time geophysical estimates of geomagnetic disturbance induced substation voltages with DC and AC power flow simulations on increasingly realistic models of the topology and state of regional power grids. We are integrating our workflow with the open source PowerModelsGMD.jl power flow simulator developed at Los Alamos National Laboratory, and describe simulations of real-time assessments of stress on critical assets of the power grid including reactive power loss, phase deviations, transformer heating and other metrics of transmission system stress. Such efforts to provide a real-time assessment of risk to critical assets can also inform statistical assessments of system vulnerabilities to "100-yr" or "Carrington" level geomagnetic disturbances. We will discuss how such efforts are informing the development of updated standards that may impact the future regulatory environment that governs efforts to maintain a resilient power transmission system. 

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3. Optical polarization–based seismic and water wave sensing on transoceanic cables

   https://doi.org/10.1126/science.abe6648  

   Zhan, Zhongwen; Cantono, Mattia; Kamalov, Valey; Mecozzi, Antonio; Müller, Rafael; Yin, Shuang; Castellanos, Jorge C. (February 2021, Science)

   null (Ed.)

   Seafloor geophysical instrumentation is challenging to deploy and maintain but critical for studying submarine earthquakes and Earth’s interior. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an opportunity to fill the data gap. We successfully sensed seismic and water waves over a 10,000-kilometer-long submarine cable connecting Los Angeles, California, and Valparaiso, Chile, by monitoring the polarization of regular optical telecommunication channels. We detected multiple moderate-to-large earthquakes along the cable in the 10-millihertz to 5-hertz band. We also recorded pressure signals from ocean swells in the primary microseism band, implying the potential for tsunami sensing. Our method, because it does not require specialized equipment, laser sources, or dedicated fibers, is highly scalable for converting global submarine cables into continuous real-time earthquake and tsunami observatories. 

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4. MVDC Bipolar Power Cables with Rectangular Geometry Design for Envisaged All-Electric Wide-Body Aircraft

   https://doi.org/10.1109/TPEC60005.2024.10472255  

   Saha, Anoy; Ghassemi, Mona (February 2024, 2024 IEEE Texas Power and Energy Conference (TPEC))

   Designing power cables that provide high power and low system mass is one of the major goals in achieving the future all-electric wide-body aircraft. Radiative and convective heat transfers from a cable's surface to the surrounding air determine how much current is permitted to flow through it. At a cruising altitude of 12.2 km (18.8 kPa) for wide-body aircraft, the limited heat transfer by convection poses thermal issues for the design of aircraft cables. These thermal challenges are exacerbated for bipolar electric power systems (EPS), which are usually made up of two power lines next to each other. The cable's surface area affects both convective and radiative heat transfers. Changing the shape of the cable is one technique to improve heat transfers and compensate for the reduced convective heat transfer caused by low air pressure. In comparison to cylindrical and cuboid cables, the rectangular geometry design gives a bigger contact area with the surrounding atmosphere for the same cross-section area, hence it is anticipated that the heat transfer would rise and as a result, the cable's maximum power-carrying capability will be higher. The purpose of this paper is to design ±5 kV bipolar MVDC power cables with rectangular geometry to raise the maximum current carrying capacity of the cable and analyze its performance with bipolar cylindrical and cuboid geometries. 

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5. Integrating space weather and ground-based magnetotelluric data with powerflow solutions for real-time assessment of risk to the power grid

   Schultz, A (April 2019, https://cpaess.ucar.edu/sites/default/files/documents/2019/2019%20Space%20Weather%20Workshop%20Draft%20Agenda%20with%20Abstracts.pdf)

   The National Space Weather Action Plan, NERC Reliability Standard TPL-007-1,2 associated FERC Orders 779, 830 and subsequent actions, emerging standard TPL-007-3, as well as Executive Order 13744 have prepared the regulatory framework and roadmap for assessing and mitigating the impact on critical infrastructure from space weather. These actions have resulted in an emerging set of benchmarks against which the statistical probability of damage to critical components such as power transmission system high-voltage transformers can be assessed; for the first time the impacts on the intensity of geomagnetically induced currents (GICs) due to the spatial variability of the geomagnetic field and of the Earth’s electrical conductivity structure can be examined systematically. While at present not a strict requirement of the existing reliability standards, there is growing evidence that the strongly three-dimensional nature of the electrical conductivity structure of the North American crust and mantle (heretofore ‘ground conductivity’) has a first-order impact on GIC intensity, with considerable local and regional variability. The strongly location dependent ground electric field intensification and attenuation due to 3-D ground conductivity variations has an equivalent impact on assessment of risk to critical infrastructure due to HEMP (E3 phase) sources of geomagnetic disturbances (GMDs) as it does for natural GMDs. From 2006-2018, Oregon State University (OSU) under NSF EarthScope Program support, installed and acquired ground electric and magnetic field time series (magnetotelluric, or MT) data on a grid of station locations spaced ~70-km apart, at 1161 long-period MT stations covering nearly ⅔ of CONUS. The US Geological Survey completed 47 additional MT stations using functionally identical instrumentation, and the two data sets were merged and made available in the public domain. OSU and its project collaborators have also collected hundreds of wider frequency bandwidth, more densely-spaced MT station data under other project support, and these have been or will be released for public access in the near future. NSF funding was not available to make possible collection of EarthScope MT data 1/3 of CONUS in the southern tier of states, in a band from central California in the west to Alabama in the east and extending along the Gulf Coast and Deep South. OSU, with NASA support just received, plans to complete MT station installation in the remainder of California this year, and with additional support both anticipated and proposed, we hope to complete the MT array in the remainder of CONUS. For this first time this will provide national-scale 3-D electrical conductivity/MT impedance data throughout the US portion of the contiguous North American power grid. Complementary planning and proposal efforts are underway in Canada, including collaborations between OSU, Athabasca University and other Canadian academic and industry groups. In the present work, we apply algorithms we have developed to make use of real-time streams of US Geological Survey, Natural Resources Canada (and other) magnetic observatory data, and the EarthScope and other MT data sets to provide quasi-real time predictions of the geomagnetically induced voltages at high-voltage transmission system transformers/power buses. This goes beyond the statistical benchmarking process currently encapsulated in NERC reliability standards. We seek initially to provide real-time information to power utility control room operators, in the form of a heat map showing which assets are likely experiencing stress due to induced currents. These assessments will be ground-truthed against transmission system sensor data (PMUs, GIC monitors, voltage waveforms and harmonics where available), and by applying machine learning methods we hope to extend this approach to transmission systems that have sparse or non-existent GIC monitoring sensor infrastructure. Ultimately by incorporating predictive models of the geomagnetic field using satellite data as inputs rather than real-time ground magnetic field measurements, a near-term probabilistic assessment of risk to transformers may be possible, ideally providing at least a 15-minute forecast to utility operators. There has been a concerted effort by NOAA to develop a real-time geomagnetically induced ground electric field data product that makes use of our EarthScope MT data, which includes the strong impacts on GICs due to 3-D ground conductivity structure. Both OSU and the USGS have developed methods to determine the GIC-related voltages at substations by integrating the ground electric fields along power transmission line paths. Under National Science Foundation support, the present team of investigators is taking the next step, of applying the GIC-related voltages as inputs to quasi-real time power flow models of the power transmission grid in order to obtain realistic and verifiable predictions of the intensity of induced GICs, the reactive power loss due to GICs, and of GIC effects on the current and voltage waveforms, such as the harmonic distortion. As we work toward integration of predicted induced substation voltages with power flow models, we’ve modified the RTS-GMLC (Reliability Test System Grid Modernization Lab Consortium) test case (https://github.com/GridMod/RTS-GMLC) by moving the geographic location of the case to central Oregon. With the assistance of LANL we have the complete AC and DC network of the RTS-GMLC case, and we are working to integrate the complete case information into Julia (using the PowerModels and PowerModelsGMD packages of LANL), or into PowerWorld. Along a parallel track, we have performed GIC voltage calculations using our geophysical algorithm for a realistic GMD event (Halloween event) for the test case, resulting in GIC transmission line voltages that can be added into our power system model. We’ll discuss our progress in integrating the geophysical estimates of transformer voltages and our DC model using LANL's Julia and PowerModelsGMD package, for power flow simulations on the test case, and to determine the GIC flows and possible impacts on the power waveforms in the system elements. 

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