Space Weather Effects on Power Systems
D. H. Boteler
Geomagnetic Laboratory, Geological Survey of Canada, Ottawa, Canada
Space weather disturbances cause geomagnetic field variations that induce electric
currents into power transmission systems on the ground. These geomagnetically
induced currents (GIC) flow to ground through the windings of power transformers
where they produce extra magnetic flux that can saturate the transformer core. This
leads to transformer heating, increased power demand, and ac harmonic generation,
which can interfere with power system operation. This paper examines the magnetic
disturbances on March 24, 1940, February 11, 1958, August 4, 1972, and March 13,
1989 that were responsible for the most significant power system effects. The blackout
of the Hydro-Quebec system on March 13, 1989 was due to an enhancement of a
westward substorm electrojet resulting from loading and unloading of energy in the
magnetosphere. Power system effects, including transformer overheating, later on
March 13 can be attributed to an eastward convection electrojet caused by the 'directlydriven' flow of energy from the solar wind. Power system problems during the earlier
disturbances are also shown to be caused by rapid changes of the convection electrojets.
This shows that the convection current systems, as well as substorm currents, need to
be included when predicting space weather effects on power systems.
1. INTRODUCTION
The first magnetic storm that had a noticeable effect on
power systems occurred on March 24,1940 (Davidson, 1940).
Power systems were again affected during the magnetic storm
of February 10, 1958; however, it was not until 1967 that
detailed investigations began (Slothower and Albertson, 1967).
In the following years an extensive investigation was made by
Alberston and co-workers who showed how widespread was
the occurrence of geomagnetically induced currents (GIC) and
the range of effects they could have on power systems
(Albertson et al, 1973,1974). Some of their recording systems
were still deployed during the major magnetic disturbance on
August 4, 1972 and this became one of the best documented
GIC events (Albertson and Thorson, 1974).
Space Weather
Geophysical Monograph 125
Copyright 2001 by the American Geophysical Union
347
During solar cycle 21 there were no major effects on power
systems due to magnetic disturbances. However, a number of
studies gathered more information about the processes involved
and how to model them. In Finland, Pirjola and co-workers
made a long series of GIC recordings and developed techniques
for calculating the electric fields and GIC produced in a power
system during geomagnetic disturbances (Pirjola, 1985;
Lehtinen and Pirjola, 1985; Pirjola and Lehtinen, 1985). In
North America, Bolduc and Aubin (1978) showed how to
calculate the transformer saturation produced by GIC, Boteler
et al (1989) reported observations of the increased ac
harmonics that result from saturation, and Albertson et al
(1981) and Kappenman et al (1981) studied how these
geomagnetic effects influenced power system operation.
In spite of the aforementioned studies, the arrival of the
magnetic storm on March 13, 1989, during the up-swing of
solar cycle 22, and its effects on power systems came as a
surprise. The storm was one of the largest recorded since
observations began in the 1840s and produced widespread
technological effects (Allen et al, 1989). Power systems in
348 SPACE WEATHER EFFECTS ON POWER SYSTEMS
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1 Effects on land line services
Figure 1. The March 24, 1940 magnetic disturbance (as shown by
hourly means from Cheltenham) plus the .times of power system
problems.
North America and Europe experienced relay trips, voltage
drops, and transformer heating. The most significant effect was
a blackout of the Hydro-Quebec power system.
Space weather affects power systems because geomagnetic
field variations induce electric currents into the power
transmission lines. These GIC flow to and from ground
through the windings of power transformers and cause partial
saturation of the transformer core. This disrupts the ac
operation of the transformer causing extra heating that can
damage winding insulation, increased reactive power demand
leading to a drop in system voltage, and higher levels of ac
harmonics which can trigger tripping of protective relays. In
extreme cases, the combination of all these things can have
serious effects on system stability and lead to a power blackout
such as occurred on the Hydro-Quebec system.
There are a number of possibilities for preventing these
space weather effects. Some transformers (3-phase 3-legged
core type) are less susceptible to saturation from GIC.
However changing existing transformers to this type is
uneconomic and for handling high power levels a 3-phase
transformer in one unit becomes impractically large and sets of
3 single-phase transformers are used instead. An alternative
approach involves blocking the flow of GIC. Hydro-Quebec
have placed blocking capacitors in their power transmission
lines, and Kappenman et al (1991) have developed a suitable
device for insertion in transformer neutral-ground connections.
These remedies are not considered economic for all systems
and many power system operators rely on advance warning of
magnetic storms to implement operating strategies designed to
reduce system vulnerability.
Several studies have been made to assess the geomagnetic
hazard to particular power systems (Makinen, 1993; Boteler et
al, 1997). Such work can determine, in general statistical terms,
the size of GIC that can be expected during different levels of
geomagnetic activity. However, in real-time forecasting we are
trying to predict the GIC and power system response that will
be produced by specific events. To help in this endeavour it is
worth looking at exactly what characteristics of past
disturbances produced significant effects on power systems.
This paper presents a summary of the power system effects and
examines their cause for the four magnetic disturbances that
have had the biggest impact on power systems: March 24,1940;
February 10, 1958; August 4, 1972; and March 13, 1989.
Identifying the magnetospheric and ionospheric current systems
responsible for the critical geomagnetic field variations should
help in forecasting future space weather effects on power
systems.
2. MARCH 24, 1940
On Easter Sunday 1940 a magnetic storm produced wide­
spread effects on power systems and communication systems.
Germaine (1940) reports that effects on land line services
occurred between 10.00 and 16.00 Eastern standard time
(EST). Davidson (1940) provides detailed accounts of the
power system problems, including the following items:
Minneapolis area:
10.45 am to 1.45 pm EST power system disturbances
11.50 am EST most severe power surges
Central Maine:
10.50 am to 2.00 pm EST numerous voltage dips
11.48 am EST two transformer banks tripped out
Eastern Pennsylvania:
11.48 am EST reactive power surges of 20% and
two 75,000 KVA transformer banks tripped
Chats Falls, Ontario:
11.48 am EST four transformers tripped out
These reports show that the peak of the disturbance
occurred just before local noon in eastern North America.
The original magnetic observatory recordings of the March
24, 1940 magnetic storm have been lost or were off scale.
However some information about the disturbance can still be
obtained from the archived hourly mean values. Figure 1
shows the hourly mean values from Cheltenham magnetic
observatory (Geograph. Lat. 38.7 Long. 283.2) on the east
coast of the United States. This shows that the power system
problems occurred at the time of large negative change in the
northward magnetic field. Such a change would be produced
by enhancement of an overhead westward electric current.
3. FEBRUARY 10-11,1958
A major magnetic storm occurred on February 10-11,1958
and produced effects on a number of power systems in North
America. Slothower and Albertson (1967) report large reactive
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Figure 2. Magnetogram from Agincourt and reactive power flow in
Minnesota showing the increase in reactive power flow at 02.00 UT
concides with an increase in magnetic activity.
power flows seen on the Northern States Power Company lines
at Minnesota. In Ontario transformers at Port Arthur and
Raynor Generating Station were simultaneously tripped by
differential relay operation (Acres, 1975). Figure 2 shows that
the start of increased reactive power flow and the transformer
trips coincided with a sudden increase in magnetic activity at
02.00 UT recorded at the Agincourt Magnetic Observatory near
Toronto. A sudden jump in the magnetic field was also
recorded on the rapid-run magnetogram at Fredericksburg
(Winckler et al, 1959).
The Fredericksburg magnetogram shows a positive
excursion in H at the time of the power system problems.
Agincourt magnetic recordings were off scale for the worst part
of the storm, however notes of the daily extremes made by the
observatory operators (Ross and Evans, 1962) record that a
maximum positive excursion of 949 nT occurred at 02.53 UT
on February 11. Both the Fredericksburg and Agincourt
magnetic excursions indicate that an eastward electrojet was
responsible for the magnetic disturbance that caused the power
system effects in Minnesota and Ontario.
began at 22.42 UT. At this time there was also an outage of the
L4 communication cable system in the mid-western United
States. An investigation by Anderson et al (1974) found that
the system outage coincided with a particularly rapid change of
the magnetic field. The disturbance was centred over western
Canada with a peak rate of change of magnetic field intensity of
2200nT/min. The disturbance extended down over the midwestern United States, and the rate of change of the magnetic
field at the cable location was estimated to be 700 nT/min.
Satellite observations showed that at the time of the power
system and cable disturbances there was a severe compression
of the magnetopause and Anderson et al (1974) concluded that
currents on the magnetopause were responsible for the
magnetic field variations that caused the problems. However,
recent model calculations by Boteler and Jansen van Beek
(1999) have shown that the observed magnetic disturbance was
too localised to have been caused by magnetopause currents.
Contour plots of the disturbance are instead consistent with an
ionospheric current as the source. Equivalent current plots
(Figure 3) derived from the observed magnetic field variations
show that a rapid intensification of an eastward electrojet was
responsible for the magnetic disturbance and the power system
and cable problems.
5. MARCH 13, 1989
On March 13,1989 power systems experienced one of the
largest magnetic storms ever recorded.
The resulting
geomagnetically induced currents caused widespread problems.
4. AUGUST 4,1972
On August 4,1972 a magnetic storm produced widespread
effects on power systems in the United States and Canada
(Albertson and Thorson, 1974; Acres, 1975). These included
tripping of transformers and capacitor banks, increased reactive
power demand and voltage drops. The most pronounced effects
Figure 3. Equivalent current vectors derived from ground magnetic
field hourly mean values centred at 22.30 UT, Aug 4, 1972. The
length of the vectors indicates the size of the currents.
350 SPACE WEATHER EFFECTS ON POWER SYSTEMS
found of heating on the phase B transformer of Salem unit 2
and this transformer was removed from service and had to be
replaced (Balma, 1992).
Because the transformer damage was only discovered after
the storm it is not possible to unequivocally identify which
phase of the disturbance was the cause. However, data from the
Fredericksburg magnetic observatory, near the Allegheny and
PJM systems, can be used to show when these systems
experienced the largest disturbance. Figure 6 shows the largest
disturbance was a positive excursion in B at approximately
22.00 UT (17.00 EST) which coincides with the power system
problems mentioned earlier. This suggests the transformer
damage on the Allegheny and PJM systems was caused by the
eastward electrojet that occurred in the evening sector on March
13.
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Figure 4. Magnetic variations on March 13, 1989 at Ottawa and the
times of power system problems.
In North America these effects occurred at six times during the
storm as shown in Figure 4 (Boteler and Jansen van Beek,
1993). In addition, damage due to transformer heating was
detected after the storm.
The most significant effect produced by the March 13,
disturbance was the Hydro-Quebec blackout.
Technical
descriptions of the power system problems are given by Czech
et al (1992) and Blais and Metsa (1993). The system collapse
at 07.45 UT coincided with the onset of a magnetic substorm
associated with the rapid increase of a westward electrojet.
Widespread power system problems also occurred later in
the storm at 21.58 UT. Equivalent current plots derived from
the magnetic observatory recordings show that there was a
strong eastward electrojet extending across North America at
this time (Figure 5).
On March 14 the Meadow Brook 500/138 kV power
transformer on the Allegheny power system was removed from
service because of evidence of heating (Gattens et al, 1989).
Inspection found 4 areas of discolored paint on Phases 1 and 2
coils on both HV and LV sides. Calculations showed that total
saturation of the core would produce a temperature of400°C in
part of the transformer tank. Gattens et al estimated that GIC of
80 A would have been necessary to produce the damage that
was found.
Seven days after the storm, routine tests on the
Pennsylvania, New Jersey, Maryland (PJM) system found
indications of transformer overheating at the Salem nuclear
power station (Balma, 1992). Further tests later in March
confirmed this evidence and the transformers were removed
from service. Subsequent inspection showed damage in the A
phase and C phase transformers of Salem unit 1 and the
transformers had to be replaced. In phase B, the damage was
not as severe. However, in September 1989 evidence was
6. DISCUSSION
The ionospheric currents responsible for the magnetic
disturbances that affect power systems at mid to high latitudes
are associated with two different processes in the
magnetosphere (see Rostoker, 1991; McPherron, 1995).
Eastward and westward convection electrojets in the evening
and morning sectors are part of a two cell current circulation in
the polar cap and auroral zone. This results from convection of
magnetic field lines within the magnetosphere which is directly
driven by coupling of energy from the solar wind. In the
midnight sector a westward substorm electrojet occurs as a
result of disruption of a cross-tail current and its diversion
Figure 5. Equivalent current vectors derived from ground magnetic
field observations at 21.58 UT, March 13, 1989.
BOTELER 351
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Figure 6. Magnetic variations on March 13, 1989 recorded at
Fredericksburg, showing the disturbance at 22.00 UT experienced by
the Allegheny and PJM systems.
through field-aligned currents into the ionosphere. This is part
of a sequence involving loading of energy into the tail of the
magnetosphere and its subsequent unloading into the auroral
ionosphere. It has generally been thought that the directlydriven convection electrojets vary slowly, and that only the
loading and unloading of energy leading to the substorm
electrojet would cause the rapid magnetic field variations that
produce power system problems.
Reviewing the disturbances considered in this paper can
give a guide to the current systems responsible for major power
system effects. The Hydro-Quebec blackout on March 13,
1989, was caused by the rapid intensification of a nightside
westward electrojet and represents a good example of problems
due to the substorm process of loading and unloading of energy
in the magnetosphere. However, power system effects later in
the day were caused by an eastward electrojet which is part of
the directly-driven convection current system. This indicates
that the convection current system, as well as the substorm
current system, can vary fast enough to cause power system
problems.
Of the earlier disturbances, both the power system effects
and the L4 cable outage on August 4, 1972 and the power
system effects on February 10, 1958 have been shown to
coincide with eastward electrojets. The eastward electrojet is
unambiguously identified with the convection current system so
the cause of the disturbances in these two cases is clear.
The power system problems in eastern North America on
March 24, 1940 are associated with a westward ionospheric
current which can be produced by either the substorm or
convection systems. In this case the location of the disturbance
near local noon excludes the substorm current system as the
cause. If the disturbance is due to the convection current
system there should be a simultaneous increase in the eastward
electrojet in the evening sector. At the time of the disturbance
observatories in Europe were in the evening sector and show a
positive change in the northwards magnetic field indicative of
a strong eastward electrojet. These observations are consistent
with the two-cell convection current system with an eastward
electrojet in the evening sector over Europe and a westward
electrojet in the morning and extending round to noon over
North America.
The events presented here are not claimed to be a complete
list of space weather disturbances affecting power systems.
Also, this analysis has concentrated on effects to power systems
in North America and a similar analysis needs to be done to
trace the cause of power system effects in Europe and other
regions. No conclusions can therefore be drawn about the
relative importance of the substorm or convection current
systems in causing GIC problems. However the results
presented here show that the convection current system can
vary fast enough to cause significant GIC effects. Thus both
the substorm and convection current systems need to be
considered when trying to predict space weather effects on
power systems.
7. CONCLUSIONS
Space weather effects on power systems have been reported
for the last sixty years. Particularly significant effects were
observed in North America during major disturbances on
March 24, 1940, February 10, 1958, August 4, 1972, and
March 13,1989. The effects range from relay trips and voltage
dips to a widespread blackout and transformer damage.
The March 13,1989 power system effects can be linked to
two different ionospheric current systems. The Hydro-Quebec
blackout and effects on other power systems at 07.45 UT were
caused by the sudden enhancement of a westward substorm
electrojet. In contrast, power system effects at 21.58 UT were
produced by an eastward convection electrojet. Transformer
damage, discovered later, was likely also caused by this
eastward electrojet.
Power system effects during the August 4, 1972 and
February 10, 1958 disturbances were produced by rapid
changes of an eastward electrojet produced by a sudden
increase in magnetospheric convection.
On March 24, 1940 power system problems in North
America occurred just before local noon and were associated
with a westward ionospheric current. This coincided with an
eastward electrojet in the evening sector which is indicative of
an enhanced convection current system.
Both the loading and unloading substorm process and the
directly driven convection process can produce sudden changes
of the ionospheric currents and the large magnetic field changes
that cause power system problems.
352 SPACE WEATHER EFFECTS ON POWER SYSTEMS
Acknowledgements. This work was funded by the Geological
Survey of Canada and Ontario Hydro. I am grateful to Dr L.
Trichtchenko, G. Jansen van Beek, and R. Libbey for help with the
preparation of this paper.
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Report TR-100450,1992.
Davidson, W.F., The magnetic storm of March 24,1940 - effects in the
power system, Edison Electric Institute Bulletin, July 1940.
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