Solar storms and their hazardous influence on the grid and nuclear power plants: Cause, events, technical solutions

Solar storms and their hazardous influence on the grid and nuclear power plants:

Cause, events, technical solutions

S.A. Meiss, F. Seidel, M. Krauss

Department SK: Nuclear Safety, Federal Office for Radiation Protection (BfS), Salzgitter, Germany

There is a permanent stream of charged particles emitted by the sun. This stream of particles interacts with the earth’s magnetic field, usually leading to a steady-state type distortion. However, from time to time coronal mass ejections (CME) take place and the stream of particles intensifies significantly and rapidly to a so-called “solar storm”. This solar storm’s interaction with the earth’s magnetic field is unsteady and leads to rapid fluctuations of the earth’s magnetic field, especially in the auroral zones in the northern and southern hemisphere.

These fluctuations of the magnetic field can induce currents in the ground and in large-scale metallic infrastructures. The first infrastructures where these geomagnetically induced currents (GIC) were observed regularly, were the lines of the telegraph system in the middle of the 19th century. Today GICs are being observed e.g. in pipelines, railways lines and especially in electric grids.

GICs can affect electrically grounded equipment that is directly connected to the grid, therefore constituting a short circuit for the GIC. Reports on overheating and even destruction of transformers, capacity banks etc. in commercial power plants - including nuclear power plants (NPP) [1] - are mostly, but not exclusively, to be found for power plants connected to grids near the auroral zones. GICs have the potential for damaging multiple devices in one or several power plants. Therefore they can lead - and have led - to widespread grid blackouts [2].

Since GICs are being observed only since about 150 years due to the lack of susceptible technical infrastructures before the mid 19th century, there are no long-term experiences about the frequency of occurrence of extreme events of this kind. However one of the strongest event reported in the literature led not only to northern lights that could be seen as far south as Rome (Italy) in 1859, but also to a nearly global disruption of the telegraph system of that time and fires in several telegraph offices [3].

Modeling of the consequences for an extreme GIC event on the modern power infrastructure in the U.S. shows e.g. a widespread long-term blackout with a significant loss rate of extra high voltage transformers in the susceptible regions [4]. This is of special interest for NPPs, as NPPs require access to external power for a safe long-term shutdown phase and for restart.

Technical solutions for modern power plants in Sweden and Canada include modified transformers that are less prone to effects from GICs and protective capacitor banks [5, 6]. Non-Technical solutions include the installation of pre-warning systems for power grid and power plant operators based on data from space weather centers in the USA (NOAA/NWS SWPC) and Europe (SWENET ).

Literature

[1]        NRC Information Notice No. 90-42, (1990)

[2]        T.S. Molinksi, IEEE spectrum, 37(11), (2000) 55-60

[3]        G.B. Prescott, History, Theory and Practice of the Electric Telegraph, Boston: Ticknor and Fields, (1860)

[4]        J.G. Kappenman, The Vulnerability of the U.S. Electric Power Grid to Severe Space Weather           Events, and Future Outlook in Severe Space Weather Events--Understanding Societal and          Economic Impacts:A Workshop Report, National Academic Press, Washington, (2008)

[5]        ABB, feature article, ABB engineering protects power plant from solar storms, (2006), online:            http://www.abb.com/cawp/seitp202/c99eb3b89c85b7b2c12571c6004579aa.aspx [25.02.2011]

[6]        T.S. Molinksi, J. Atmos. Sol.-Terr. Phy., 64, (2002) 1765-1778

The referenced NRC Information notice 90-42 was based upon the following events in 1989:

Specific events occurred at theThree Mile Island Unit 1, Hope Creek Unit 1, and Salem Unit 1 nuclear power plants. –tripping of capacitor banks in the 500-kilovolt substation.
–swings in reactive electrical power and –six operations of the main generator negative sequence alarm,
–generatorstep-up transformer,[…]severe overheating, melted low-voltage service connections in phases A and C, and insulation discoloration in phase B.
–a second solar storm: damage to a generator step-up transformer.

The experience is that solar flares can magnetically induce large currents, but equipment and procedures have coped with it in the past.