From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 310.
ph ph
0 1 ph N
ph 0
1
0
V V
Z Z I 3 K
I 3I
3 Z
I
Z = =
- + ×
+ ×
×
EQUATION1275 V3 EN-US (Equation 310)
Where:
Vph is phase to ground voltage at the relay point.
Iph is phase current in the faulty phase.
3I0 is ground fault current.
Z1 is positive sequence impedance.
Z0 is zero sequence impedance.
Z0m
A B
21 21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN-US
Figure 192: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure
193.
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 193: Equivalent zero sequence impedance circuit of the double-circuit,
parallel, operating line with a single phase-to-ground fault at the
remote busbar
1MRK 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 405
Application manual
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