ABB RELION REX640 Technical Manual page 1104

Section 5
Protection related functions
1098
The identification of the faulty phases is compulsory for the correct operation of
SCEFRFLO. This is because only one of the impedance-measuring elements (fault
loops) provides the correct result for a specific fault type. A three-phase fault is an
exception and it can be calculated with any of the fault loops. The fault loop used in
the fault distance calculation is indicated in the recorded data Flt loop as specified in
Table 1042.
Table 1042: Fault types and corresponding fault loops
Fault type
-
A-E
B-E
C-E
A-B
B-C
C-A
A-B-C-(E)
In case of two-phase-to-earth-faults (A-B-E, B-C-E or C-A-E), the selected fault loop
depends on the location of the earth faults. When the faults are located at the same
feeder, the corresponding phase-to-phase loop ("AB Fault", "BC Fault" or "CA
Fault") is used for calculation. When the faults are located at different feeders, the
phase-to-earth loop ("AG Fault", "BG Fault" or "CG Fault") corresponding to the
faulty phase at the protected feeder is used for calculation.
Fault impedance and distance calculation
As soon as a fault condition is recognized by Phase selection logic, the fault distance
calculation is started with one of the seven impedance-measuring elements, that is, the
fault loops. SCEFRFLO uses independent algorithms for each fault type to achieve
optimal performance.
The inherent result from the fault distance calculation is the ohmic fault loop
impedance value.
Table 1043: The calculated impedance values available in the recorded data
Impedance value Description
Flt phase reactance Estimated positive sequence reactance from the substation to the fault
location in primary ohms
Flt point resistance Fault resistance value in the fault spot in primary ohms. The composition of
this term depends on the fault loop as described in the following subsections.
Flt loop resistance The total fault loop resistance from the substation to the fault location in
primary ohms. Fault point resistance is included in this value. The
composition of this term is different for short-circuit and earth-fault loops as
described in the following subsections.
Flt loop reactance The total fault loop reactance from the substation to the fault location in
primary ohms. The composition of this term is different for short-circuit and
earth-fault loops as described in the following subsections.
Description
No fault
Phase A-to-earth fault
Phase B-to-earth fault
Phase C-to-earth fault
Phase A-to-B short circuit fault
Phase B-to-C short circuit fault
Phase C-to-A short circuit fault
Three-phase short circuit
1MRS759142 C
Flt loop
No fault
AG Fault
BG Fault
CG Fault
AB Fault
BC Fault
CA Fault
ABC Fault
REX640
Technical Manual