ABB Relion 670 Series Technical Reference Manual page 206

Section 6
Impedance protection
200
VA
Phase-to-ground
fault in phase A
0
VA
Phase-to-phase
fault in phase A-B
VB
VA
Three-phase
fault
VC
ANSI05000181 V2 EN
Figure 91: Fault loop model
The R1 and jX1 in figure
measuring point to the fault location. The RFPG and RFPP is the eventual fault
resistance in the fault place.
Regarding the illustration of three-phase fault in figure 91, there is of course fault
current flowing also in the third phase during a three-phase fault. The illustration
merely reflects the loop measurement, which is made phase-to-phase.
The zone may be set to operate in Non-directional, Forward or Reverse direction
through the setting OperationDir. The result from respective set value is illustrated in
figure 92. It may be convenient to once again mention that the impedance reach is
symmetric, forward and reverse direction. Therefore, all reach settings apply to both
directions.
R1 + j X1
Ip
IN
(R0-R1)/3 +
j (X0-X1)/3 )
R1 + j X1
IA
IB
R1 + j X1
R1 + j X1
IA
IC
R1 + j X1
91 represents the positive sequence impedance from the
1MRK505222-UUS C
Phase-to-ground
element
RFPG
(Arc + tower
resistance)
Phase-to-phase
element A-B
RFPP
(Arc resistance)
0.5·RFPP
Phase-to-phase
element A-C
0.5·RFPP
ANSI05000181_2_en.vsd
Technical reference manual