From symmetrical components, it is possible to derive the impedance Z at the IED
point for normal lines without mutual coupling according to equation 35.
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 35)
Where:
Vph is phase-to-ground voltage at the IED 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 72: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, as shown in figure
73.
1MRK 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 197
Application manual
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