VA
R1 + j X1
Ip
RFPG
Phase-to-ground
fault in phase A
Phase-to-phase
fault in phase A-B
Three-phase
fault
(Arc + tower
resistance)
0
(R0-R1)/3 +
j (X0-X1)/3 )
IN
VA
R1 + j X1
IA
VB
R1 + j X1
IB
RFPP
VA
R1 + j X1
IA
VC
R1 + j X1
IC
0.5·RFPP
0.5·RFPP
(Arc resistance)
Phase-to-ground
element
Phase-to-phase
element A-B
Phase-to-phase
element A-C
ANSI05000181_2_en.vsd
ANSI05000181 V2 EN-US
Figure 74: Fault loop model
The R1 and jX1 in figure 74 represents the positive sequence impedance from the 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
74, 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 75. The impedance
reach is symmetric, in the sense that it conforms for forward and reverse direction (there are
different forward and reverse settings - Zx and ZxRev respectively, where x = 1 - 5). Therefore, all
reach settings apply to both directions.
1MRK 502 066-UUS B Section 7
Impedance protection
187
Technical manual
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