IEEE Electrification Magazine - December 2015 - 4

TecHNOLOGY LeAderS

Geomagnetic Effects
on Power Systems
By David Boteler

N APRIL 1940, POWER SYStems in parts of the United
States and Canada experienced problems that coincided with
disturbances in the Earth's magnetic
field that were traced back to activity
on the sun a few days earlier. Since
then, this solar connection to power
systems has both fascinated and frustrated power system engineers trying
to understand how such things could
happen. Pioneering work by Prof. Vernon Albertson at the University of
Minnesota and coworkers in the
1960s and 1970s laid the ground work
for our understanding. However, it
was not until the magnetic storm of
March 1989-the largest of the last
century-that the issue began to be
taken seriously.
On 6 March 1989, a complex sunspot region-Region 5395-appeared
around the edge of the visible face of
the sun. Over the next two weeks, carried by the sun's rotation, the sunspot
region crossed the face of the sun
unleashing solar flares and eruptions
of plasma. Solar flares are intense
bursts of electromagnetic radiation
that can cause problems for radio
communications but do not affect
power systems. However, they are
often accompanied by eruptions of
plasma from the solar corona. These
coronal mass ejections (CMEs) travel

Digital Object Identifier 10.1109/MELE.2015.2480555
Date of publication: 2 December 2015

out from the sun, taking between one
and three days to travel the distance
to Earth. In March 1989, CMEs associated with massive solar flares on 6
and 17 March would have shot into
space behind or ahead of Earth. However, CMEs associated with solar flares
on 9 and 10 March when Region 5395
was near center disk, would be on a
collision course with Earth.
On 13 March, at 01:28 Universal
Time (UT), a sudden jump in the magnetic field recorded at magnetic observatories across North America and
beyond heralded the arrival of the
shock wave at the front edge of a CME
as it compressed the magnetic field on
the day side of the Earth. Over the next
36 h, the interaction of the CME with
the Earth's magnetic field produced a
variety of electric currents in its ionosphere and magnetosphere, resulting
in a series of magnetic disturbances on
the ground. Electrons and protons circulating in opposite directions in the
radiation belts produce the magneticstorm main phase: a depression of the
Earth's magnetic field lasting 12-36 h.
Electric currents in the ionosphere-
the auroral electrojets-produce shortlived (15-60-min) variations called
magnetic substorms. The charged particles associated with these currents
also give rise to the aurora borealis-
the northern lights-and the aurora
australis, the only visible manifestations of the disturbance that is underway in the magnetic field.

I E E E E l e c t r i f i c ati o n M agaz ine / december 2015

Each surge of activity produced
magnetic-field variations that induced
electric currents in the Earth and in
long conductors, such as power systems, pipelines, and phone cables at
the Earth's surface. In power systems,
these geomagnetically induced currents (GICs), flow along transmission
lines and through transformer windings and neutral-ground connections
of substations (principally) at the ends
of the lines. GICs have low frequencies
(<1 Hz) compared to the ac power system frequency, so they are often
referred to as quasi-dc when talking
about their interaction with power
system components. In the power
transformers, the extra magnetic field
associated with GICs produces a dc
offset in the operating point of the
transformer and combined with the
ac magnetic field can push the transformer core into saturation for part of
each ac cycle. This partial saturation
results in a spiky magnetizing current
waveform, causing high harmonic levels that can cause misoperation of
protection relays. Partially saturated
transformers also draw more reactive
power, which, if not supported, can
lead to voltage sag. In addition, leakage of magnetic flux can create hot
spots in the transformer windings and
support structures, possibly damaging
the transformer.
On 13 March 1989, a series of magnetic substorms caused surges of GICs
through many power systems.
2325-5987/15©2015IEEE

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2015