ABB RELION REX640 Technical Manual page 1204

Protection related functions
Flt loop resistance
Flt loop reactance
Figure 686: Fault loop impedance for phase-to-phase fault loops (either "AB Fault",
"BC Fault" or "CA Fault")
The fault distance calculation algorithm for the phase-to-phase fault loops is
defined by using settings
for the selection are "Disabled" or "Enabled".
Load compensation can be enabled or disabled with setting
Load compensation should be disabled only if the ratio between the fault current
and load current is high or when the value of the fault distance estimate for the
short circuit fault is required from each shot of an autoreclosing sequence.
The fault distance calculation is most accurate when calculated with the fault loop
model. This model requires positive-sequence impedances of the protected feeder
to be given as settings. If these settings are not available, valid impedance values
can be calculated also without the fault loop model with setting
model = "Enabled". However, a valid distance estimate, that is, the conversion
of measured impedance ("electrical fault distance'') into a physical fault distance
requires accurate positive-sequence impedance settings.
Fault loop "ABC Fault"
Fault loop "ABC Fault" is used exclusively for the three-phase short circuit fault.
Figure 687
measured and stored in the recorded data of SCEFRFLO.
Flt point resistance
Flt loop resistance
Flt loop reactance
1204
R
fault
R
= +
1
2
Flt phase reactance
=
Load Com PP loops and Enable simple model . Options
shows the three-phase fault loop model. The following impedances are
R
=
fault
R R
= +
fault
1
Flt phase reactance
=
X
=
1
X
=
1
1MRS759142 F
(Equation 300)
(Equation 301)
Load Com PP loops .
Enable simple
(Equation 302)
(Equation 303)
(Equation 304)
REX640
Technical Manual