BLOCK
SWING
OPERATE
Blocking
logic
OSB
Impedance
calculation
Out of step
detection
DISABLE
OSB_Z2
SWING_OP
I
1
I
2
U
1
I3P
U3P
Figure 559: Functional module diagram
Impedance calculation
This module calculates the positive-sequence impedance (Z1) using positive-
sequence voltage and current. For the module to calculate impedance it is required
that the positive-sequence current is above
Min Ps Seq current
setting and the
negative-sequence current is below the
Max Ng Seq current
setting.
The calculated positive-sequence impedance amplitude Z1_AMPL and angle
Z1_ANGLE are available in ohms and degrees, respectively, in the Monitored data
view.
The calculated impedance is converted to ohms as the operating
characteristics are defined with the ohm settings.
Out of step detection
The operating characteristic is a circular offset mho on the impedance plane with
two pair of blinders. The mho characteristic is defined with the
Forward reach
,
Reverse reach
, and
Impedance angle
settings.
Forward reach
defines the impedance
from the origin to the edge of circle on the top side.
Reverse reach
defines the
impedance from the origin to the edge of the circle on the bottom side. The
diameter of the mho characteristics is the sum of
Forward reach
and
Reverse reach
settings. Two sets of blinders are defined by
Inner blinder R
and
Outer blinder R
intercepting at R-axis. The blinders are at the same angle as the
Impedance angle
.
The second blinder of each outer and inner pair is automatically made symmetrical
with the origin of the R-X plane.
For a correct operation, it is required that the setting for
Inner blinder R
is less than the setting for
Outer blinder R
.
The circular mho characteristic can be further divided into two zones by setting
Zone 2 enable
to “Yes”. The boundary between zones is set using the setting
Zone 1
reach
. The lower portion of the circle, Zone 1, is separated from the upper portion,
Zone 2, by a line, perpendicular to the blinders, located at a set percentage of the
Forward reach
setting from the origin.
1MRS759142 F
Protection functions
REX640
Technical Manual
1007
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