Abstract
Geomagnetically induced currents (GICs) are induced in electrical power transmission networks during geomagnetic disturbances. Understanding the magnitude and duration of the GIC expected during worst‐case extreme storm scenarios is vital to estimate potential damages and disruptions to power networks. In this study we utilize the magnetic field waveforms measured during three large geomagnetic storms and scale them to expected worst case extreme storm magnitudes. Multiple methods are used to simulate the varying magnitude of the magnetic field across the different latitudes of New Zealand. Modeled GIC is produced for nine extreme storm scenarios, each covering 1–1.5 days in duration. Our industry partners, Transpower New Zealand Ltd provided GIC magnitude and duration levels which represent a risk to their transformers. Using these thresholds various extreme storm scenarios predict between 44 and 115 New Zealand transformers (13%–35%) are at risk of damaging levels of GIC. The transformers at risk are largely independent of the extreme storm time‐variations, but depend more on the latitude variation scenario. We show that these at‐risk transformers are not localized to any specific region of New Zealand but extend across all regions and include most of the major population centers. A peak mean absolute GIC over a 60‐min window of 920–2,210 A and an instantaneous 1‐min time resolution maximum GIC of 1,590–4,920 A occurs for a worst‐case extreme storm scenario. We believe this is one of the first studies to combine a reasonable worst‐case extreme geomagnetic storm with validated GIC modeling and industry‐provided GIC risk thresholds.
Plain Language Summary
Space Weather events can cause unwanted DC currents in electrical power transmission networks during geomagnetic storms. We model multiple difference extreme storms to determine the worst case DC currents expected. We work with our industry partners in New Zealand to determine DC magnitudes and durations that would put different types of transformers at risk. Using these values we predict multiple transformers are at risk of damaging levels of DC current. We show that the transformers at risk are located throughout all regions of New Zealand. We believe this is one of the first studies that combines multiple extreme storms scenarios with industry provided DC current magnitudes and durations to determine the risk to transformers.
Key Points
Magnetic fields from large geomagnetic events imposed with different latitude variations can produce theoretical extreme storm scenarios
Extreme storm scenarios consistently predict between 13% and 35% of New Zealand transformers reaching dangerous levels of long lasting Geomagnetically induced current (GIC)
The transformers at most risk of long lasting GIC are not confined to a small region, instead spread throughout the length of New Zealand