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 709.
Table 709: Fault types and corresponding fault loops
Fault type
Description Flt loop
- No fault No fault
A-E Phase A-to-ground fault AG Fault
B-E Phase B-to-ground fault BG Fault
C-E Phase C-to-ground fault CG Fault
A-B Phase A-to-B short circuit fault AB Fault
B-C Phase B-to-C short circuit fault BC Fault
C-A Phase C-to-A short circuit fault AC Fault
A-B-C-(E) Three-phase short circuit ABC Fault
In case of two-phase-to-ground faults (A-B-E, B-C-E or C-A-E), the selected fault loop
depends on the location of the individual ground faults. When the faults are located at the
same feeder, the corresponding phase-to-phase loop (either “AB Fault” or “BC Fault” or
“CA Fault”) is used for calculation. When the faults are located at different feeders, the
phase-to-ground loop (either “AG Fault” or “BG Fault” or “CG Fault”) corresponding to
the faulty phase at the protected feeder is used for calculation.
5.7.4.2 Fault impedance and distance calculation
As soon as a fault condition is recognized by the phase selection logic, the fault distance
calculation is started with one of the seven impedance-measuring elements, that is, the
fault loops. 21FL employs 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 710: The calculated impedance values available in the recorded data
Impedance valule
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 ground-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 ground-faults
loops as described in the following subsections.
Section 5 1MAC059074-MB A
Protection related functions
806 615 series ANSI
Technical Manual
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