ABB RELION REX640 Technical Manual page 477

1MRS759142 C
REX640
Technical Manual
Operation is achieved when the measured admittance moves outside the
characteristic.
The combined overadmittance and overconductance criterion is applicable in
unearthed, high-resistance earthed and compensated networks or in systems where the
system earthing may temporarily change during normal operation from compensated
network to unearthed system.
Compared to the overadmittance criterion, the combined characteristic improves
sensitivity in high-resistance earthed and compensated networks. Compared to the
non-directional overconductance criterion, the combined characteristic enables the
protection to be applied also in unearthed systems.
GUID-5E898D95-9CFC-40D6-9CE9-C52BEA3CB570 V1 EN
Figure 256: Combined overadmittance and overconductance characteristic. Left
figure: classical origin-centered admittance circle combined with two
overconductance boundary lines. Right figure: admittance circle is
set off from the origin.
Combined overconductance and oversusceptance characteristic
The combined overconductance and oversusceptance criterion is enabled with the
Operation mode setting set to "Go, Bo".
By setting Directional mode to "Forward", the characteristic is a combination of two
boundary lines with the settings Conductance forward and Susceptance forward. See
Figure 257.
By setting Directional mode to "Non-directional", the characteristic is a combination
of four boundary lines with the settings Conductance forward, Conductance reverse,
Susceptance forward and Susceptance reverse. See
For the sake of application flexibility, the boundary lines can be tilted by the angle
defined with the Conductance tilt Ang and Susceptance tilt Ang settings. By default,
the tilt angles are zero degrees, that is, the boundary lines are straight lines in the
admittance plane. A positive Conductance tilt Ang value rotates the overconductance
Section 4
Protection functions
Figure 258.
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