ABB RELION REX640 Technical Manual page 885

1MRS759142 C
Ph Pref logic Hi Imp
5 Acyc A-B-C
6 Acyc A-C-B
7 Acyc B-A-C
8 Acyc B-C-A
9 Acyc C-A-B
10 Acyc C-B-A
REX640
Technical Manual
Faulted loops
A & B XC_FLT B & C XC_FLT
RELEASE_PE
AB Fault BC Fault
AB Fault BC Fault
AB Fault BC Fault
AB Fault BC Fault
AB Fault BC Fault
AB Fault BC Fault
Faulted loop phase selection for low-impedance earthed networks
The faulted loop selection logic for low-impedance earthed networks serves as a
supplement to the faulted phase identification function and it provides a selective
filtering of measurement elements in case of a two-phase-to-earth fault in low-
impedance earthed networks. The earth faults can be located close to each other.
R1
Z<
S
CB1
A
B
C
GUID-1AAAB97B-435B-440A-90A0-30C9D74A2503 V1 EN
Figure 474: Two-phase-to-earth fault in low-impedance earthed system
Impedance can be measured during a two-phase-to-earth fault when the earth faults
are located in the same direction and they are in close proximity to each other.
Generally, too large an impedance is measured for the lagging phase-to-earth loop, for
example phase B in an AB-E fault. Similarly, low impedance is measured for the
leading phase-to-earth loop, for example phase A in an AB-E fault. The corresponding
phase-to-phase loop is measured correctly, for example phase-to-phase loop AB in an
AB-E fault.
C & A XC_FLT A & B XC_FLT
RELEASE_PP
CA Fault AB Fault
CA Fault AB Fault
CA Fault AB Fault
CA Fault AB Fault
CA Fault AB Fault
CA Fault AB Fault
Section 4
Protection functions
B & C XC_FLT C & A XC_FLT
BC Fault CA Fault
BC Fault CA Fault
BC Fault CA Fault
BC Fault CA Fault
BC Fault CA Fault
BC Fault CA Fault
R2
Z<
R
CB2
879