Abstract
AbstractLarge geomagnetic storms are a known space weather hazard to power transmission networks due to the effects of geomagnetically induced currents (GICs). However, research in this area has been hampered by a lack of GIC observations. Previous studies have noted that New Zealand is unusually fortunate in having a comparatively dense, high quality, set of GIC measurements, spanning >60 transformers in >20 substations. However, due to operational reasons these observations are clustered in the mid and lower South Island. In this paper we analyze space weather‐induced GIC impact patterns over the entire country by using a different set of sensors that monitor levels of harmonic distortion, with even and odd harmonics measured separately. GICs lead to half cycle transformer saturation and is one of the few ways in which even harmonics are produced in a well‐run power transmission network. We make use of harmonic distortion measurements at 377 circuit breakers made at 126 separate locations. Focusing on the intense geomagnetic storm activity during 6–9 September 2017, we show how the even harmonic distortion observations provide a useful new picture of GIC‐stressed transformers. These observations demonstrate how GIC effects can be monitored by using even harmonic distortion in locations where no GIC measurements are present (e.g., the most of the North Island). We understand that harmonic distortion measurements are fairly common in electrical networks and could provide a new tool for space weather researchers.
Highlights
There is a rising global recognition of space weather as a hazard to our deeply technologically connected society
Until now there have been limited simultaneous harmonic distortion experimental observations and geomagnetically induced currents (GICs) measurements presented in the literature
One reason for this may be that most countries have limited GIC measurements available to link to the harmonic distortion observations
Summary
There is a rising global recognition of space weather as a hazard to our deeply technologically connected society. The transformer at Dunedin/Halfway Bush (HWB T4) failed within 1 min of the storm start (Béland & Small, 2004; Mac Manus et al, 2017; Marshall et al, 2012) In recent years this has stimulated a focus on space weather impacts on the New Zealand electrical network, exploiting the significant quantity of DC GIC observations available in parts of that country (Mac Manus et al, 2017). These measurements showed increases in even‐order harmonics once GIC levels measured at the monitored transformers at the Halfway Bush substation exceeded 15 A, in one case for >30 min. The harmonic distortion observations provide new insights into the occurrence of GIC leading to transformer saturation
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