ABB RET670 Applications Manual page 175

1MRK504116-UUS C
Application manual
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 51.
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 59.
V
ph
Z = =
-
Z Z I
0 1 ph
+ ×
I 3I
ph 0
×
3 Z
1
EQUATION1275 V2 EN
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
A
21
ANSI05000221 V1 EN
Figure 51: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure 52.
V
ph
+ ×
3I K
0 N
FAULT
Z0m
Section 3
IED application
(Equation 59)
B
21
en05000221_ansi.vsd
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