Space weather – a hidden threat to power systems

Solar storms with the potential to disrupt power and other systems including railways are coming into the spotlight as the next solar maximum approaches.

As Europe experiences record high temperatures, many people’s thoughts have turned to the weather and the power of the heat of the sun and its impact on the environment.

For most people, the impacts are based on factors such as humidity, cloud cover and wind, not to mention the time of year. But for infrastructure, apart from the damages from the extremes of heat or cold, it is the impacts of the small natural variations the sun undergoes, unseen except by instruments, that are potentially the more significant.

Such variations, styled as space weather or solar or geomagnetic storms, result from changes in the solar magnetic fields and occur on an approximately 11-year cycle. The next solar maximum, reflected in increasing solar activity, is expected around mid-2025.

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The sun’s behaviour and the causes of irradiance variations – amounting to about 0.1% – are the subject of much study but broadly it is well known over many years that as its magnetic fields interact, they can trigger ejections of magnetically charged radiation.

These, known as ‘coronal mass ejections’ or solar flares (depending on the scale and other factors), can interact in turn with the magnetic field of the earth with potentially widespread consequences, including damage to power grid components and power and communication outages through the induced current driven into the respective networks.

For example, on March 13 1989, a solar storm caused among other impacts a 9-hour blackout for 5 million people across the entire power grid in the province of Quebec in Canada – with secondary impacts but no outages at connected US utilities – and the destruction of a transformer in New Jersey.

Train signal disruption

While the potential power grid impacts of space weather have been well known for years, new research at Lancaster University is focusing on another known but little understood phenomenon – that of interfering with railway signalling and turning green signals to red even when no train is nearby and potentially, and more dangerously, from red to green.

To track the location of trains, a railway line is split into small, consecutive ‘blocks’ with an average length of 1-2km. Each block is tied to a signal that notifies if there is a train currently in that block.

The signals are controlled by relays which detect currents in the system. Synonymous to traffic lights, the signals turn green if the block is empty and a current is detected, or red if the block is occupied and no current is detected.

The researchers have been investigating the impacts of solar storms on two segments of Britain’s railway network: a south-north line from Preston to Lancaster and a west-east line from Glasgow to Edinburgh.

Technological problems are found to have the potential to occur not only in the stronger storms with electric field strengths of 4V/km but also in the more moderate storms of 2V/km. In the past, values of higher than 7V/km have been detected along railways in Sweden, while estimates of extreme solar storms have predicted events with strengths of up to 20V/km.

“Most of us have at one point heard the dreaded words ‘your train is delayed due to a signalling failure’, and while we usually connect these faults to rain or snow on the line, you may not have considered that the sun can also cause railway signals to malfunction,” comments doctoral student Cameron Patterson.

“We are now working on looking at the case where trains are present on the line, and how strong a storm needs to be to turn a red signal back to green – a far more hazardous scenario potentially leading to crashes!”

Dealing with space weather

The largest storm recorded is the so-called Carrington Event of September 1859, estimated about three times stronger than the March 1989 event and which caused widespread failures of telegraph systems including fires in some in the US and Europe among other impacts.

Geological evidence suggests even stronger storms might have occurred in the past, with such a storm generally attributed to the Miyake Event of ca AD774, in which the largest and most rapid rise of the carbon-14 isotope known has been recorded. A major source of 14C is cosmic rays, which are triggered in increased numbers in a solar storm.

In the electricity industry, protections such as capacitors and relays are available. Nevertheless, for example, David Wallace, Assistant Clinical Professor of Electrical Engineering at Mississippi State University, believes that a Carrington Event-size storm would be “extremely damaging” to the electrical and communication systems worldwide with outages lasting into the weeks.

One the size of the Miyake Event would be “catastrophic” with potential outages lasting months if not longer.

The consensus is that a major solar storm will hit the earth at some time and it is not a matter of ‘if’ but ‘when’.

In the meantime, utilities could do worse than sign up to the US National Weather Service’s space weather warnings and alerts giving perhaps as little as minutes but up to hours advance notice of events for which mitigating actions might be needed.