From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 82.
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 82)
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 99: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure
100.
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 100: Equivalent zero sequence impedance circuit of the double-circuit,
parallel, operating line with a single phase-to-ground fault at the
remote busbar
1MRK 502 071-UUS A Section 8
Impedance protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 237
Application manual
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