Geomagnetic storms are caused by coronal mass ejections (CMEs) — explosions of plasma from the sun that are shot into space.
A CME was detected early yesterday, and more were occurring, meaning more geomagnetic storms may hit today.
When CMEs interact with Earth’s atmosphere, they create colourful Aurora Australis displays, but they can also interact with Earth’s magnetic field, disrupting it and inducing additional electrical currents down long electricity transmission lines.
When the currents reach transformers in substations or at large hydro-electric dams, they have the potential to cause extensive damage.
A Transpower spokesman said removing the circuits from service yesterday did not have any impact on consumers’ electricity supply, but it was an important and necessary step to prevent damage — especially if the solar storms got worse.
"To minimise the risk of damage to critical equipment, Transpower may work with industry to switch off some parts of the power system for a time in an extreme solar storm.
"These events are rare, but we are prepared for them and have a plan in place.
"If we don’t do this and equipment is damaged, it could require expensive and time-consuming repairs, or the total replacement of equipment."
In a statement on Thursday morning Transpower said the space weather event had passed, and it had lifted the grid emergency "now that the G4 geomagnetic storm has reduced in severity".
"The South Island electricity transmission lines that were removed from service as a precaution to prevent damage to equipment have now been returned to service. There was no impact on consumers’ electricity as a result of the storm."
University of Otago physics Professor Craig Rodger said the vast majority of CMEs usually went unnoticed because Earth’s magnetic field shielded us from the charged solar particles.
But on the rare occasions that they did get through, they could cause a geomagnetic storm, affecting electricity grids, radio signals, navigation systems, satellites and other infrastructure.
For several years, he has been working with Transpower to develop protocols for dealing with space weather and protecting New Zealand’s electricity grid.
Some of those protocols were used during yesterday’s geomagnetic storm, to reduce the magnitude of additional currents which might have damaged the grid.
On the bright side, he said the storm appeared to be continuing and another coronal mass ejection was on its way toward Earth, so it was possible more Aurora Australis would be seen tonight, if the skies were clear.
Auroras are formed when charged particles from the CMEs collide with oxygen and nitrogen in Earth’s atmosphere, causing them to release energy in the form of light which creates the colourful displays overhead.
