Parallel line in service
This type of application is very common and applies to all normal sub-transmission and
transmission networks.
Let us analyze what happens when a fault occurs on the parallel line see figure 114.
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation
112.
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 (Equation 341)
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
Figure 190: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure 115.
Section 8 1MRK 506 369-UUS -
Impedance protection
392 Line distance protection REL670 2.2 ANSI
Application manual
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