Power grids across North America and Europe have been on high alert all week as two massive solar storms have battered Earth, threatening to disrupt electricity supplies to millions of homes and businesses.
On Monday, PJM Interconnection, which coordinates power to 61 million people across 13 US states and the District of Columbia, alerted generators and transmission companies as the first storm was upgraded from “strong” to “severe” by the US government’s Space Weather Prediction Center (SWPC) in Boulder, Colorado.
Controllers across the United States and Canada have been issuing similar warnings and preparing to stabilize their grids as unusually strong electromagnetic radiation emitted from the sun interacts with the Earth’s own magnetic field and induces freak currents across the electricity transmission network.
A second storm is set to peak around 23:00 GMT on Wednesday, when highly charged particles which erupted from the surface of the Sun on Monday are forecast to reach Earth, according to the SWPC.
Grid controllers aim to prevent a repeat of the events of the night of March 13-14, 1989, when a geomagnetic storm induced severe currents on high voltage power lines near the US-Canadian border and created a cascading failure which knocked out the entire Hydro-Quebec power grid in just 92 seconds.
Relays automatically disconnected transmission lines and generation units to protect the equipment from serious damage and power was restored to 83 percent of affected customers within nine hours of the system’s collapse.
But two large generator step-up transformers were damaged by excessive voltage in the 1989 storm. The threat to large high-voltage transformers worries industry executives and regulators because networks carry only a limited stock of spares and it could take months to manufacture, deliver and install replacements.
Geomagnetic disturbances are listed alongside cyber and physical attacks, pandemics and the electromagnetic pulse from the high-altitude detonation of a large nuclear weapon as high impact low frequency risks to the power network by the North American Electric Reliability Corporation.
Damage from the 1989 solar storm was largely confined to the Hydro Quebec network but bigger storms in 1921 and 1859 caused extensive damage to telegraph networks across the United States and Europe.
Policymakers are concerned that if and when such storms are repeated the impact could be much worse given how central electricity has become to the modern economy.
The fear is that if an extreme storm damaged dozens or even hundreds of high-voltage transformers over a large area it would not be possible to replace them all quickly.
In the United States, the Federal Energy Regulatory Commission has ordered the industry to develop operating procedures to mitigate the impact of geomagnetic disturbances and test equipment to ensure it can handle the sort of currents which could be unleashed by a major storm.
There is uncertainty about just how much damage even a severe solar storm would do to high-voltage transformers. Some in the industry argue most modern transformers could survive the excess current flows and heating likely to be associated even with a 1-in-100 year storm.
Nonetheless, major modelling exercises are underway across North America to assess how a storm might affect the networks and to identity transformers most at risk.
In the meantime, power networks have issued their control room staff with operating procedures to follow in the event of a storm warning to reduce the risks of a catastrophic failure.
The Space Weather Prediction Center, part of the US National Oceanic and Atmospheric Administration, uses a series of satellites between the Sun and the Earth to identify eruptions and estimate the timing and severity of storms arriving on Earth.
Warnings are flashed electronically to grid controllers, transmission operators and power generators around the world to enable them to ready their systems as much as possible to withstand abnormal currents.
Guidance issued to grid controllers authorises them to take emergency measures to reduce the pressure on the network to enable it to deal with the extra demands imposed by a solar storm.
These include calling up additional generation, reducing loading on the system, and instructing transmission companies to discontinue maintenance and bring out-of-service lines back into full operation.
Grid operators are still conducting the studies required by regulators into how their networks would cope with a really severe storm and identifying vulnerabilities; in the meantime the onus falls to control rooms to render their networks as stable as possible and try to ride out the storm.