Current efforts to assess risk to the power grid from geomagnetic disturbances (GMDs) that result in geomagnetically induced currents (GICs) seek to identify potential "hotspots," based on statistical models of GMD storm scenarios and power distribution grounding models that assume that the electrical conductivity of the Earth's crust and mantle varies only with depth. The NSF-supported EarthScope Magnetotelluric (MT) Program operated by Oregon State University has mapped 3-D ground electrical conductivity structure across more than half of the continental US. MT data, the naturally occurring time variations in the Earth’s vector electric and magnetic fields at ground level, are used to determine the MT impedance tensor for each site (the ratio of horizontal vector electric and magnetic fields at ground level expressed as a complex-valued frequency domain quantity). The impedance provides information on the 3-D electrical conductivity structure of the Earth’s crust and mantle. We demonstrate that use of 3-D ground conductivity information significantly improves the fidelity of GIC predictions over existing 1-D approaches.
We project real-time magnetic field data streams from US Geological Survey magnetic observatories into a set of linear filters that employ the impedance data and that generate estimates of ground level electric fields at the locations of MT stations. The resulting ground electric fields are projected to and integrated along the path of power transmission lines. This serves as inputs to power flow models that represent the power transmission grid, yielding a time-varying set of quasi-real-time estimates of reactive power loss at the power transformers that are critical infrastructure for power distribution.
We demonstrate that peak reactive power loss and hence peak risk for transformer damage from GICs does not necessarily occur during peak GMD storm times, but rather depends on the time-evolution of the polarization of the GMD’s inducing fields and the complex ground (3-D) electric field response, and the resulting alignment of the ground electric fields with the power transmission line paths. This is informing our efforts to provide a set of real-time tools for power grid operators to use in mitigating damage from space weather events.
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This content will become publicly available on April 23, 2025
Completion of the MT Survey and its Contribution to Geoelectric Field Calculations
For the past 18-years Oregon State University and its contractors - under the support of NSF (2006-2018), NASA (2019-2020) and USGS (2020-2024)- installed temporary (weeks-to-months; at 7 Backbone stations - years) long-period MT stations that measure ground-level vector electric and magnetic fields on a 70-km grid of points spanning the conterminous US.
A total of 1711 transportable stations whose data meet data quality control standards will have been installed, operated and extracted by mid-2024, completing the MTArray in CONUS.
We generate MT Impedance tensors (“EMTF”s, induction vectors and related quantities from the MT time series, suitable for determining the 3-D electrical structure of the crust and upper mantle.
The impedances, induction vectors, and/or derived 3-D electrical models can be used to estimate ground-level electric fields from measurements or models of ground-level magnetic fields. These can be integrated along the paths of power grid transmission lines and
flowed through power grid equivalent electrical circuits to determine GIC intensity, transformer heat and vibration, and reactive power loss.
A look to the future: With a sufficiently dense, real-time telemetering network of MT stations, we have demonstrated how a convolutional neural network trained on measured time series from an array of MT stations may be used to forecast ground-level fields
more than 30-minutes in the future, and the potential this has for alerting power utilities of incoming risks to specific HV transformers on the transmission network (reported at this workshop in 2022).
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- Award ID(s):
- 1720175
- NSF-PAR ID:
- 10513322
- Publisher / Repository:
- https://www.swpc.noaa.gov/sites/default/files/images/u97/2024%20SWW%20Detailed%20Agenda%20%28Presentations%29.pdf
- Date Published:
- Subject(s) / Keyword(s):
- Magnetotelluric Electric Field Predictions Forecasting Geomagnetically Induced Currents
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Geomagnetically induced currents (GICs) result from the interaction of the time variation of ground magnetic field during a geomagnetic disturbance with the Earth's deep electrical resistivity structure. In this study, we simulate induced GICs in a hypothetical representation of a low‐latitude power transmission network located mainly over the large Paleozoic Paraná basin (PB) in southern Brazil. Two intense geomagnetic storms in June and December 2015 are chosen and geoelectric fields are calculated by convolving a three‐dimensional (3‐D) Earth resistivity model with recorded geomagnetic variations. The
dB /dt proxy often used to characterize GIC activity fails during the June storm mainly due to the relationship of the instantaneous geoelectric field to previous magnetic field values. Precise resistances of network components are unknown, so assumptions are made for calculating GIC flows from the derived geoelectric field. The largest GICs are modeled in regions of low conductance in the 3‐D resistivity model, concentrated in an isolated substation at the northern edge of the network and in a cluster of substations in its central part where the east‐west (E‐W) oriented transmission lines coincide with the orientation of the instantaneous geoelectric field. The maximum magnitude of the modeled GIC was obtained during the main phase of the June storm, modeled at a northern substation, while the lowest magnitudes were found over prominent crustal anomalies along the PB axis and bordering the continental margin. The simulation results will be used to prospect the optimal substations for installation of GIC monitoring equipment.
