Power grids face unexpected slow-burn threat from solar storms

As countries electrify more of their economies and increasingly interconnect their power grids, understanding space weather has become crucial. One particularly adverse form of space weather is a geomagnetic storm: temporary disturbances in earth’s magnetic field caused by charged particles from the sun. These storms produce beautiful aurorae but also induce strong yet short-lived currents in the grid.

However, a new study in Space Weather has reported that these storms can also stress power grids in a hitherto unexpected way and that existing tools may not fully capture the effects. The findings are centred on a geomagnetic storm in June 2015 that the U.S. Space Weather Prediction Centre had rated G4, or ‘severe’, and which produced a strange effect in New Zealand.

Instead of briefly and intensely spiking the strength of currents in the South Island power grid, the storm ramped up geomagnetically induced currents over 90 minutes. The currents amounted to only 20 amperes but the duration was interesting, per the study. When such a current flows through a transformer for long periods, it can saturate the magnetic core, leaving them to overheat and suffer more wear.

The study data came from multiple datasets plus measurements provided by Transpower New Zealand.

The researchers — from the University of Gothenburg, Sweden — traced the cause to a possible “mid-latitude ionospheric current wedge”. That is, the storm had appeared to divert a part of the electric current that encircles earth in space, called the ring current, into the ionosphere.

Aside from the unusually prolonged current, the authors also wrote that the extant ways to track the effects of geomagnetic storms didn’t properly capture the diversion. Scientists conventionally use the rate of change of earth’s horizontal magnetic field, denoted H’, to understand the extent of the geomagnetically induced current. But during the June 2015 event, H’ did not sufficiently correlate with the grid currents. The wedge also distorted some of the parameters commonly used to assess geomagnetic storms.

The authors also found that the risk of these unusual events depends on how well the local ground conducts electricity and the layout of power lines. On South Island itself, they found two substations just 5 km apart recorded disparate current levels.

They concluded that experts need to update their understanding of the ways in which adverse space weather could be dangerous. and suggested that protective measures could not afford to focus on spiking currents alone.