ABB RELION 620 Series Technical Manual page 792

Section 10
Recording functions
786
Fault loop determination
Any fault can be categorized as either a phase-to-phase fault or a phase-to-ground fault.
The fault loop determination algorithm determines whether the fault is a phase-to-ground
fault or phase-to-phase fault by comparing the phase currents to the zero-sequence
current.
Fault loop determines the fault loop from pre-fault and fault phasor stored in the respective
buffers. The fault typing is the procedure to identify the type of fault, and therefore the
respective voltage and current phasor can be selected from the pre-fault and fault buffers
for the fault location algorithm.
Once the fault has been classified as either a phase-to-ground or phase-to-phase fault, the
specific fault loop is determined by comparing all the phase currents to the setting Phase
Level. Fault loop determination is done in accordance with
Table 568: Fault identification
Fault in phase A Fault in phase B
1 0
0 1
0 0
1 1
0 1
1 0
1 1
1 1
0 1
1 0
1 1
0 0
Once the specific fault type is determined, the respective fault loop voltage and current
phasor are taken for fault location algorithm.
If the fault is any single phase-to-ground fault, the respective phase current should be
ground-compensated.
The procedure for the ground compensation is given below,
For ground fault cases, the current measured at the protection relay is ground-
compensated by employing the following formula
Table
Fault in phase C Fault in ground
(Io)
0 1
0 1
1 1
0 0
1 0
1 0
1 0
0 1
1 1
1 1
1 1
0 0
1MAC504801-IB E
568.
FLTLOOP FLTLOOP
AG Fault 1
BG Fault 2
CG Fault 3
AB Fault 4
BC Fault 5
CA Fault 6
ABC Fault 7
ABG Fault -1
BCG Fault -2
CAG Fault -3
ABCG -4
Fault
No Fault 0
620 series ANSI
Technical Manual