ABB RELION REX640 Technical Manual page 929

1MRS759142 C
REX640
Technical Manual
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.
Section 4
Protection functions
923