ABB RELION REX640 Technical Manual page 906

Section 4
Protection functions
900
One alternative for polarization is also "Self pol" despite the drawbacks when using it
as a polarization method. The mho circle does not expand when using this polarization
method.
In case of cross and positive-sequence polarization, the expansion of the mho circle is
a positive feature as the fault resistance coverage is increased. The reach of the zone
is not affected by the expansion. The greatest expansion is obtained with cross-
polarization.
The directional offset mho is explicitly defined by the reach settings and is thus fixed
in the impedance plane. The polarization method does not expand this circle even for
directional mode. However, directional lines criteria are defined using polarized
signals.
X
X1 zone x
α
R1 zone x
α
-X1 reverse zone x
GUID-F0C2A55F-B253-49DC-978C-C406D2D91AAF V1 EN
Figure 493: Tripping characteristic for phase-to-phase or three-phase
impedance measuring elements ifImpedance Chr PP Zn is "Mho
(circular)" and Directional mode Znx is "Non-directional". On the left,
Impedance mode Zn is "Rectangular". On the right, Impedance mode
Zn is "Polar".
R
1MRS759142 C
X
R
REX640
Technical Manual