ABB Relion 670 Series Technical Reference Manual page 184

Section 6
Impedance protection
178
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 77: Fault loop model
The R1 and jX1 in figure
measuring point to the fault location. The settings RFPG and RFPP are the eventual
fault resistances in the faulty place.
Regarding the illustration of three-phase fault in figure 77, 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 can 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 78. The impedance reach is symmetric, in the sense that it conforms for forward
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
77 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