When the parallel line is out of service and not grounded, the zero sequence on that line
can only flow through the line admittance to the ground. The line admittance is high which
limits the zero sequence current on the parallel line to very low values. In practice, the
equivalent zero sequence impedance circuit for faults at the remote bus bar can be
simplified to the circuit shown in figure
118
The line zero sequence mutual impedance does not influence the measurement of the
distance protection in a faulty circuit.
A
B
C
IEC09000255_1_en.vsd
I
0
I
0
Z
0m
Z
0
-
Z
0m
Z
0m
Z
0
-
IEC09000255 V1 EN
Figure 157: Equivalent zero sequence impedance circuit for a double-circuit line with
one circuit disconnected and not grounded.
8.9.2.7 Tapped line application
C
A
B
BC
ANSI05000224-2-en.vsd
ANSI05000224 V2 EN
Figure 158: Example of tapped line with Auto transformer.
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 323
Application manual
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