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.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 687
Technical Manual
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