IEEE Electrification Magazine - December 2015 - 44

200
150
100

(km)

50
0

2 V/km

-50
-100

50 A

-150

30 A
15 A
5A
100-A System
Equivalent

-200
-250

-400 -300 -200

-100
(km)

0

100

200

Figure 11. A snapshot of the DVP system at time t = 6.1667 h in a 100year solar storm. The magnitude and direction of the geoelectric field is
indicated by the arrow. The diameter of the circles indicates the magnitude
of GIC (amps per phase) at the power transformers. System equivalents
(at the boundary of the system) are represented by squares. (Source: DVP.)

scenario that may occur in a larger time scale. Dr. Bernabeu
has participated in the project to model a 100-year geoelectric-field scenario in human history (Figure 10). The findings
of the project and scientific studies of the past 200-year historical solar storm events have pointed out that the
magnetic-field and horizontal-magnetic-field distributions resulting
from a solar storm follow certain geographical patterns-the maximum
measure of the fields have significant
gaps at a latitude of 50°-55°. As
shown in Figure 11, territory above
this threshold will typically have significantly stronger magnetic fields. It
is reasonable to note that the geoelectric-field distribution is inherent
to the geographic latitude. Virginia is
below the latitude gap, so the DVP
transmission system is in an area
with relatively mild magnetic field.
The other key factor contributing
to geoelectric field is the ground
conductivity, which largely depends
on the earth composition and landscape type. Studies of
extreme ground conductivity conditions point out that the
magnetic field generates three to four times ESP on a
high-conductive ground than on a resistive ground. The
DVP system is located in a high-ground-conductivity
region; therefore, a high-ground-conductivity model has
been adopted in the geoelectric scenario study.

geoelectric-field scenario is one critical step DVP's GMD
research team has taken. A three-phase, balanced, dc
model and transformer convention is used to replicate
DVP's EHV network under GIC situations. The magnitudes of the geoelectric field E of the solar storm are
derived from the 100-year geoelectric-field scenario
introduced above. The successive procedures are executed as follows:
xx
The network's admittance matrix Y and ground
impedance matrix Z are calculated.
xx
The Norton equivalents J across transmission lines
are derived from E, Y, and Z.
xx
The ground GIC vector I is calculated as a function of
Y, Z, and J.
xx
The diagonal and off-diagonal elements of Y, Z, and
J are decoupled and multiplied by corresponding I
elements rendering the GIC line flows.
xx
The effective GIC flow through an autotransformer is
calculated with the consideration of the galvanic connection involving series and common windings and
their turns' ratios.
Following the modeling, a comprehensive study was performed to address two concerns-locations and actions. Locations where transformers are prone to experience large GICs
were identified. The findings are used in building DVP's realtime GIC visualization tool and also in identifying susceptible
locations that require additional attention in DVP's solar magnetic disturbances system operations procedures.
After locations are identified, the most
effective operational procedures to
mitigate GMD stresses are evaluated
based on an index derived from the
monitoring of all GIC flow changes
before and after the event. Analysis of
DVP's system indicates that there are
no common patterns to reduce both
line and ground GIC flows. Less intuitively, switching off transmission lines
reduces the total GIC amount; yet it
may yield higher GICs at certain transformer neutrals due to GIC flows
reforming depending on the orientation of the geoelectric field. There are
combinations of operations found that can significantly mitigate GIC impacts on specific susceptible locations under certain system operation and geomagnetic conditions.
This research work quantifies the severe consequences of a solar storm from a system level; converts geospatial information to GIC quantities that can be directly
used as a judgment reference for system operations; and
helps SOs plan and train for solar magnetic disturbances.

DVP has developed
its own GMD
visualization tool
to provide real-time
information of GIC
flows at key
locations in
the system.

44

Modeling GIC in DVP's System Using 100-Year
Geoelectric-Field Scenarios

Future Tasks

Mapping DVP's electric grid into a dc model representing
GIC activities and assessing the impact of a 100-year

DVP's GMD mitigation plans continue to be a work in
progress. The project's goal is not only to understand the

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



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

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