Monitoring and Assessment of Geomagnetically Induced Currents in Alberta’s High Voltage Network
Creators: Parry, Hannah
Publisher: name: University of Alberta Library
Year: 2022

<p>Geoelectric fields produced by time-varying magnetic fields associated with geomagnetic storms can result in potentially damaging geomagnetically induced currents (GICs) in long conductors at Earth’s surface. GICs are quasi-direct currents which have been demonstrated to pose a significant risk to the integrity of grounded electrical infrastructure, particularly to transformers in the electrical power grid. In this study, an inferred GIC is calculated using a novel configuration of the differential magnetometer measurement (DMM) method on a 500 kV transmission line in central Alberta and is validated using a traditional neutral-to-ground current measurement at a transformer substation near Edmonton, Alberta. This thesis outlines a custom-built and innovative DMM design by which both DMM sensors deployed around a power line measure the background geomagnetic disturbance (GMD) and the magnetic field generated by the GIC. This approach provides two independent calculations of GIC which are compared against the transformer neutral current measured by AltaLink L.P, one of Alberta’s largest utility companies. A developing partnership between the University of Alberta and companies within Alberta’s power industry is leveraged to validate the augmented DMM method by directly comparing the two independent DMM inferred GIC measurements to the industry GIC measurement recorded using a Hall effect sensor. Results from a moderate geomagnetic storm on October 12th, 2021 show excellent temporal correspondence and contemporaneous peaks in both GIC measurements at 6:42:49 UT and 10:54:21 UT. This exercise was successful in demonstrating a prototype for temporary deployment of the new DMM method to measure local GIC on the electrical power grid for use by industry. </p>

<p>Further, we examine the role of the Earth’s conductivity structure in driving GIC as described by the local impedance tensor. The geoelectric field is calculated through a convolution between the measured frequency-dependent impedance tensor and the magnetic field measured by the CARISMA (Canadian Array for Real-time Investigations of Magnetic Activity) magnetometer at Ministik Lake, 33 km from the transformer substation. A comparative analysis demonstrates excellent linear correlation between the calculated geoelectric field and the GIC response measured by AltaLink for three GMD events during the past year, particularly during a moderate geomagnetic storm on November 4th, 2021, R &gt; 0.7 from 2:00 to 8:00 UT. We demonstrate that the estimated geoelectric field is associated with the observed neutral-to-ground current, confirming that the GIC is driven in the electrical power network in Alberta by small and moderate GMD events. These results also prove an accurate measurement of the impedance can be utilized to diagnose the waveform of the geoelectric fields in central Alberta which are in good agreement with the GIC response in the power network. </p>

<p>In the future, continued collaboration with industry partners will be leveraged to further examine the grid response in other segments of the Alberta electrical power grid, investigate the regional variability of the geoelectric field due to Earth’s conductivity structure and its impact on the power grid GIC response, and provide a comprehensive assessment and model for the whole of the Alberta electrical transmission system.</p>