U.S. Power Grids Prepping for Solar Storms
Experts remain divided about just how much damage the grid would sustain in the event of another big solar storm, but regulators are taking a safety-first approach, ordering reliability coordinators and transmission operators to start preparing.
According to the North American Electric Reliability Corporation (NERC), the organisation which is responsible for grid reliability in the United States and Canada, the most likely consequence would be “voltage instability and subsequent voltage collapse.”
Power could be restored to customers in a matter of hours (“Special Reliability Assessment Interim Report: Effects of Geomagnetic Disturbances on the Bulk Power System” 2012).
But modelling by the U.S. Department of Energy’s Oak Ridge National Laboratory indicates a 1-in-100 year solar storm, such as those that struck the United States in 1859 and again in 1921, would cause as many as 300 high-voltage transformers to fail and suffer permanent damage.
With only very limited stocks of spare high-voltage transformers, and a lengthy lead time for ordering and manufacturing new ones, customers could be left without power for weeks or even months.
Ironically, the sun is unusually quiet at present. But the consequences of a big solar storm, if and when it arrives, would probably be much worse than a physical attack on the power network by criminals, terrorists or foreign agents .
“Should a storm of similar magnitude (to 1859 or 1921) strike today, it could interrupt power to as many as 130 million people in the United States alone, requiring several years to recover,” Oak Ridge warned (“Electromagnetic Pulse: Effects on the U.S. Power Grid” 2010).
Geomagnetic storms are a classic example of a high-impact low-frequency risk. The threat on any given day may be remote, but if it occurred, the results could be catastrophic. If a solar storm struck the planet at the wrong time of day, North America could be thrown back over a century into the pre-electric age.
And it could happen surprisingly fast. The worst geomagnetic storms are caused by coronal mass ejections (CMEs) in which billions of tonnes of highly charged particles are flung from the sun’s surface out into space in the direction of Earth and then interact with the planet’s own magnetic field.
The full fury of the storm would reach Earth in between 14 and 96 hours, according to scientists, leaving hours or at most a few days to prepare after a coronal mass ejection has been detected by satellites close to the sun (“Research on Historical Records of Geomagnetic Storms” 2005).
The National Aeronautic and Space Administration’s Advanced Composition Explorer (ACE) satellite, positioned a million miles from Earth, can give indications of an incoming storm’s potential severity but might give just 30 minutes warning, according to NERC.
Both the United States and Canada have specialist space weather forecasting centres, which use satellite data to issue forecasts, warnings and alerts about incoming solar radiation and solar storms, including to power grid operators (www.spwc.noaa.gov).
Once the storm hits, power networks can be damaged almost instantly. The 1989 solar storm brought down the whole Quebec-Hydro power system in just 92 seconds, leaving six million customers without power, according to Oak Ridge.
The same storm also triggered hundreds of incidents across the United States and burned out a major transformer at the Salem No 1 nuclear power plant in New Jersey.
As a solar storm interacts with the Earth’s own magnetic field, it produces strong geomagnetically induced currents (GICs) on the planet’s surface, which can enter the power grid at transformer stations and travel along power lines, disrupting the normal operation of the network.
NERC reckons the most likely impact would be wild fluctuations in voltage across the system. But those could still result in a cascading power failure as relays race to isolate vulnerable equipment and power plants shut down automatically.
The result might look a lot like the August 2003 blackout in the Northeast United States and neighbouring parts of Canada, when extreme swings in voltage led to the automatic shutdown of more than 500 generating units and cut power to 50 million people in five minutes.
Some customers were left without power for as much as four days as grid operators attempted to perform a “black start” on the system.
However, in the case of a geomagnetic storm, the consequences could be much more widespread, because a really large storm would hit power supplies across the entire of North America simultaneously.
The biggest risk would arise if current flows and voltage swings caused high voltage transformers to become overloaded and overheat, resulting in failure or permanent damage.
NERC admits some transformers based on older designs and nearing the end of their service lives could be vulnerable to burn out, especially if they are already heavily loaded at the time the storm hits.
The Salem No 1 transformer was of this type. When it was inspected a week later the internal windings showed signs of charring.
High-voltage transformers are not simple to replace. The power industry keeps limited spares, which are pooled among transmission operators and utilities through NERC’s Spare Equipment Database (SED) programme.
But in the event of a storm that took out dozens, or even hundreds, of high-voltage transformers, there would simply not be enough spares to go around.
The general manager of Pennsylvania Transformer, one of several manufacturers in the United States, recently told the Wall Street Journal: “I can only build 10 units a month.”
Following a really big solar storm, it might take over a year to replace all the burned out transformers.
While the industry remains divided on the extent of the danger, the U.S. Federal Energy Regulatory Commission (FERC) has ordered it to start making preparations anyway.
Order 779, issued in May 2013, instructed NERC to initiate a two-stage planning process. In the first phase, NERC was ordered to develop reliability standards that would require owners and operators of the transmission system to develop operational procedures to mitigate the impact of solar storms.
NERC has now submitted a three-point standard and submitted it to FERC for approval. Each of the regional reliability coordinators in the United States will be required to develop a geomagnetic storm operating plan and disseminate space weather forecasts to utilities and transmission operators. Transmission operators, too, will be required to develop an operating plan to show how they will respond to an incoming storm.
In some instances, that may mean cutting power
supplies and reducing the loading on vulnerable equipment to reduce the risk of overheating.
In the second stage, which is more controversial, NERC must develop standards requiring transmission owners and operators to conduct initial and ongoing assessments of how a solar storm would affect their equipment.
According to FERC, stage two will “require owners and operators to develop a plan so that instability, uncontrolled separation or cascading failures of the bulk power system, caused by damage to critical or vulnerable equipment … will not occur as a result of a (solar storm)”.
Transmission owners will not be allowed to rely on operating procedures alone. They must also develop strategies for protecting the grid “based on factors such as the age, condition, technical specifications or location of specific equipment.”
Such strategies could include “automatically blocking geomagnetically induced currents from entering the bulk power system, instituting new requirements for new equipment, inventory management, and isolating certain equipment that is not effective to retrofit.”
The industry worries that some of these measures might not be cost effective, given the uncertain danger posed to transformers, but FERC has overruled these concerns, ordering the industry to start planning for the big one.
(Editing by Veronica Brown)