IEEE Electrification Magazine - December 2015 - 16

Substation A with R = 0.2 Ω

Substation B with R = 0.2 Ω

Neutral = -21.3 V

Neutral = 21.3 V

Bus 3

Bus 1

dc = -21.3 V dc = -32.0 V
1.001 pu

0.999 pu

765 kv Line

Bus 2

Bus 4

dc = 32.0 V

dc = 21.3 V

0.997 pu

1.000 pu
Slack

3 Ω Per Phase
GIC/Phase = 35.6 Amps
High Side = 0.3 Ω/Phase

GIC Input = 170.8 V

GIC Losses = 35.5 Mvar

High Side = 0.3 Ω/Phase
GIC Losses = 17.7 Mvar

Figure 4. The four-bus test case with GICs visualized for a 1-V/km eastward electric field.

Hence, GIC calculation requires the dc resistances of the
various elements of a power system, including lines,
transformer windings, and substation grounding. These,
along with the network topology, are used to build the
GIC conductance matrix, G. A key difference between
the structure of the G matrix and the power flow Ybus is
that the G matrix has substation neutrals as nodes in
addition to buses. Also, lines with series capacitors
appear as open circuits to GICs and are modeled accordingly in G.
In G, transformers are included with their winding
resistances values between the terminal and substation
neutral, and autotransformers are considered with the
series and common winding resistances. Transformer
winding resistances can be extracted from transformer
test reports or nameplate ratings.
The substation grounding resistance used here is
meant to represent the effective grounding resistance of
the substation, consisting of the grounding mat and the
ground paths from the substation such as the presence
of shield wire grounding. Substation grounding resistance can be calculated using the fall-of-potential method

and steps described in IEEE Standard 81-1983 and its
revision, IEEE 81.2-1991. The value of grounding resistance depends on the construction of the substation
grounding grid and on the local soil and earth conditions.
In the four-bus case, the resistances of the substations and
transformers are synthetic values but similar to those that
can be expected in real systems. These can be viewed or
modified in the "Transformers" (Figure 6) and "Substations"
options under "Tables and Results."
For analyzing real power grids, ideally, the actual dc
resistance values of the system elements should be
acquired. However, in large-system cases with thousands
of transformers and substations, these data may not
always be readily available. In such cases, resistance values can be estimated using the standard data available in
the power flow model. For instance, transformer winding
dc resistance values can be estimated from the ac series
resistance of the transformer that is available in power
flow cases, knowing that, for a transformer with turns
ratio a t, a ballpark ratio of the HV to low-voltage (LV)
winding resistance is a t2 for a regular transformer and
(a t - 1) 2 for an autotransformer.

Substation A with R = 0.2 Ω

Substation B with R = 0.2 Ω

Neutral = 0.0 V

Neutral = 0.0 V

Bus 3

Bus 1

Bus 2

Bus 4

dc = 0.0 V

dc = 0.0 V

dc = 0.0 V

dc = 0.0 V

1.001 pu

0.999 pu

0.997 pu

1.000 pu

765 kv Line

Slack

3 Ω Per Phase
GIC/Phase = 0.0 Amps
High Side = 0.3
0 3 Ω/Phase

GIC Input
I
t = 0.0
00V

GIC Losses = 0.0 Mvar
Figure 5. The four-bus test case with GICs visualized for a 1-V/km northward electric field.

16

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

High Side = 0.3
0 3 Ω/Phase
GIC Losses = 0.0 Mvar



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

IEEE Electrification Magazine - December 2015 - Cover1
IEEE Electrification Magazine - December 2015 - Cover2
IEEE Electrification Magazine - December 2015 - 1
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IEEE Electrification Magazine - December 2015 - Cover3
IEEE Electrification Magazine - December 2015 - Cover4
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http://www.nxtbook.com/nxtbooks/pes/electrification_september2019
http://www.nxtbook.com/nxtbooks/pes/electrification_june2019
http://www.nxtbook.com/nxtbooks/pes/electrification_march2019
http://www.nxtbook.com/nxtbooks/pes/electrification_december2018
http://www.nxtbook.com/nxtbooks/pes/electrification_september2018
http://www.nxtbook.com/nxtbooks/pes/electrification_june2018
http://www.nxtbook.com/nxtbooks/pes/electrification_december2017
http://www.nxtbook.com/nxtbooks/pes/electrification_september2017
http://www.nxtbook.com/nxtbooks/pes/electrification_march2018
http://www.nxtbook.com/nxtbooks/pes/electrification_june2017
http://www.nxtbook.com/nxtbooks/pes/electrification_march2017
http://www.nxtbook.com/nxtbooks/pes/electrification_june2016
http://www.nxtbook.com/nxtbooks/pes/electrification_december2016
http://www.nxtbook.com/nxtbooks/pes/electrification_september2016
http://www.nxtbook.com/nxtbooks/pes/electrification_december2015
http://www.nxtbook.com/nxtbooks/pes/electrification_march2016
http://www.nxtbook.com/nxtbooks/pes/electrification_march2015
http://www.nxtbook.com/nxtbooks/pes/electrification_june2015
http://www.nxtbook.com/nxtbooks/pes/electrification_september2015
http://www.nxtbook.com/nxtbooks/pes/electrification_march2014
http://www.nxtbook.com/nxtbooks/pes/electrification_june2014
http://www.nxtbook.com/nxtbooks/pes/electrification_september2014
http://www.nxtbook.com/nxtbooks/pes/electrification_december2014
http://www.nxtbook.com/nxtbooks/pes/electrification_december2013
http://www.nxtbook.com/nxtbooks/pes/electrification_september2013
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