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