Abstract
AbstractSeveral periods of geomagnetically induced currents (GICs) were detected in the Halfway Bush substation in Dunedin, South Island, New Zealand, as a result of intense geomagnetic storm activity during 6 to 9 September 2017. Unprecedented data coverage from a unique combination of instrumentation is analyzed, that is, measurements of GIC on the single‐phase bank transformer T4 located within the substation, nearby magnetic field perturbation measurements, very low frequency (VLF) wideband measurements detecting the presence of power system harmonics, and high‐voltage harmonic distortion measurements. Two solar wind shocks occurred within 25 hr, generating four distinct periods of GIC. Two of the GIC events were associated with the arrival of the shocks themselves. These generated large but short‐lived GIC effects that resulted in no observable harmonic generation. Nearby and more distant magnetometers showed good agreement in measuring these global‐scale magnetic field perturbations. However, two subsequent longer‐lasting GIC periods, up to 30 min in duration, generated harmonics detected by the VLF receiver systems, when GIC levels continuously exceeded 15 A in T4. Nearby and more distant magnetometers showed differences in their measurements of the magnetic field perturbations at these times, suggesting the influence of small‐scale ionospheric current structures close to Dunedin. VLF receiver systems picked up harmonics from the substation, up to the 30th harmonic, consistent with observed high‐voltage increases in even harmonic distortion, along with small decreases in odd harmonic distortion.
Highlights
Rapid fluctuations of the Earth’s magnetic field can lead to geomagnetically induced currents (GIC) flowing in high-voltage transformers and power systems (Pirjola & Boteler, 2017)
very low frequency (VLF) receiver systems picked up harmonics from the substation, up to the 30th harmonic, consistent with observed high-voltage increases in even harmonic distortion, along with small decreases in odd harmonic distortion
There was unprecedented data coverage from a unique set of instruments, that is, measurements of GIC effects on the T4 transformer housed within Halfway Bush (HWB), magnetic field measurements from a magnetometer located only 7 km from HWB, VLF wideband measurements at, and near, HWB detecting the presence of power system harmonics, and voltage distortion measurements made on a 110-kV line circuit breaker connected to the T4 transformer
Summary
Rapid fluctuations of the Earth’s magnetic field can lead to geomagnetically induced currents (GIC) flowing in high-voltage transformers and power systems (Pirjola & Boteler, 2017). During a GIC event unidirectional DC flux adds to the alternating current flux in transformer cores for alternate half cycles potentially leading to peak magnetic flux levels that drive saturation. Enhanced harmonics from nearby power systems have previously been observed with a very low frequency (VLF) receiver during the sudden commencement of a geomagnetic storm as observed in Canada (Hayashi et al, 1978). We identify GIC levels that produced harmonic distortion, identify the components present, and describe the geomagnetic perturbation characteristics We suggest that this is an unusually complete set of space weather observations, providing direct evidence of GIC saturation to a transformer, along with measurements of the GIC and resultant harmonics
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