PGDTF,
Larisa extracted the following information from the NERC Application Guide.
Shunt
Devices
The
bulk
power
system
generally
uses
two
types
of
shunt
elements
to
help
control
system
voltage:
shunt
capacitors
and shunt
reactors.
Shunt
capacitors
present very
high impedance
to
the
flow
of
GIC, and
are consequently
excluded
in the dc
analysis.
Shunt
reactors
connected
directly
to
the
substation
bus
or
transmission lines,
on
the
other
hand, can
provide
a low
impedance
path
for
GIC and
should
be
included
in the
analysis.
The dc
model
of
a grounded-wye
shunt
reactor
is
the
same as
that
of
a grounded-wye
winding
of
a GSU.
If dc
winding resistance
values
are unknown,
they
can be
estimated
using
an assumed
X/R
ratio.
Note
that
X/R
ratio
of
a typical
dead-tank
shunt
reactor
can
be
far greater
than
the
X/R
ratio
of
a typical transformer
of the
same
MVA
rating.
It is not
uncommon
for
the
X/R
ratio
of large
shunt
reactors
to exceed 1000.
The
preceding
calculation
methods
use
two
particular
assumptions
in order
to
simplify
the
calculations:
1)
the
magnetic
field variations
are
uniform
over the
area
of the
power
system
and
2) the
earth
conductivity
structure
only
varies with
depth (i.e.,
there
are no
lateral
variations
in conductivity).
To
improve
the
accuracy
of
the calculated
geoelectric
fields
both
the
structure of the
source magnetic
field
and
the
lateral
variations
in conductivity
should
be
considered.
Regards,
Michael Juricek, P.E.
Chairman Planning Geomagnetic Disturbance Task Force
Asset Planning Distribution and Transmission
Oncor Electric Delivery Co LLC
Office: 214.743.6671
Mobile: 214.490.0748
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