Very low frequency emissions detected during the September 2017 space weather events
Color plot showing the spectrum of very low frequency (VLF) emissions (vertical axis) detected by a receiver close to a power grid transformer over a period of five hours (horizontal axis) during the September 2017 space weather events. Horizontal bands indicate frequencies at which significant VLF radio power is detected. The strong enhancements between 12:15 and 12:45 UTC coincide with the measurement of strong geomagnetically induced currents in the transformer. The vertical red line shows when rapid magnetic field changes were detected at an observatory some 300 km away from the transformer. Credit: Clilverd et al, 2018, Figure 6, top right panel
Source: Space Weather

Very low frequency (VLF) radio receivers are a non-intrusive means of detecting geomagnetically induced currents (GICs) in power grids, an important manifestation of space weather. When transformers within power grids are stressed by GICs, they can generate harmonics of the 50 or 60 Hz AC currents flowing across those grids. Some of the power in these harmonics is emitted as radio waves at frequencies up to a few kHz, as shown in the figure above.

The existence of these power grid VLF emissions was first recognized some forty years ago by Hayashi et al. [1978]. However, there was then very limited interest in space weather and GICs, unlike today when these are topics of global concern. Thus Clilverd et al. [2018] is an excellent and timely reminder that these VLF emissions have considerable potential as a diagnostic tool to monitor GICs in power grids without intruding on grid equipment. This could have major practical advantages in terms of safety and cost.

Citation: Clilverd, M. A., Rodger, C. J., Brundell, J. B., Dalzell, M., Martin, I., Mac Manus, D. H., et al. (2018). Long‐lasting geomagnetically induced currents and harmonic distortion observed in New Zealand during the 7–8 September 2017 disturbed period. Space Weather, 16.

—Michael A. Hapgood, Editor, Space Weather

Text © 2018. The authors. CC BY-NC-ND 3.0
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