IEEE Electrification Magazine - December 2015 - 6

TecHNOLOGY LeAderS

resistance values are then used with
network modeling techniques to
determine the GICs values throughout
the network.
GICs modeling is needed to show the
exact GICs levels for a specific power
network, but some general features are
common to all systems. Higher-voltage
transmission lines use multiple conductors and, therefore, have lower resistance
than lower-voltage lines, so the highervoltage parts of the network experience
the largest GICs. Longer lines experience
a larger induced voltage and tend to
experience larger GICs; however, if a long
line is in the middle of the network,
there is no reason for the GICs to flow to
or from ground at the ends of that line.
Instead, the GICs tend to flow across the
whole network and flow to and from

ground at the substations on the edge of
the network, and system length is more
important than the length of any individual line. The increasing use of higher
voltages with their lower-resistance
transmission lines is an increasing concern about GICs.
As awareness of GICs has increased,
there have been recordings made of
them in power systems in many parts
of the world. Generally, it had been considered as a high-latitude problem, but
there are reports from lower-latitude
systems of lines tripping, transformers
growling, and transformer damage
attributed to GICs. Thus, geomagnetic
effects on power systems are now
attracting attention around the world.
Extreme geomagnetic storms that
could cause widespread GICs problems

are (fortunately) rare events. However,
experience with other natural phenomena such as Hurricane Katrina has
changed the thinking about such highimpact, low-frequency events. A one-in100-year event could occur next year,
rather than 100 years from now, and, if
that occurs, it is better to be prepared
for it. This has stimulated new work to
assess the geomagnetic hazard to individual power systems.
Geomagnetic hazard depends on
system characteristics as explained previously, and beyond that it is all about
"location, location, location." The first
critical parameter is the size of the geomagnetic activity, and this is greatest at
higher latitudes close to the auroral
electrojet current systems. Statistical
studies have shown how the occurrence

Figure 1. Magnetic coupling between the auroral electrojet and a power transmission lines produces the induced EMf that

drives GICs.

6

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



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

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