Parallel line out of service and not earthed
SEMOD154680-242 v2
Z0m
A B
Z< Z<
en05000223.vsd
IEC05000223 V1 EN-US
Figure 141: Parallel line is out of service and not earthed.
When the parallel line is out of service and not earthed, the zero sequence on that
line can only flow through the line admittance to the earth. 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
141
The line zero-sequence mutual impedance does not influence the measurement of
the distance protection in a faulty circuit. This means that the reach of the
underreaching distance protection zone is reduced if, due to operating conditions,
the equivalent zero sequence impedance is set according to the conditions when the
parallel system is out of operation and earthed at both ends.
Z Z0
0 m
Z Z0
0
m
Z0
m
A
B
C
99000040.vsd
I
0
I
0
IEC99000040 V1 EN-US
Figure 142: Equivalent zero-sequence impedance circuit for a double-circuit
line with one circuit disconnected and not earthed.
The reduction of the reach is equal to equation 196.
( )
( )
( )
2
1 0
0
1 0
0
1 0
1
2
3
1
1
2 3
2
3
E f
m
U
f
f
Z Z R
Z
K
Z Z Z R
Z Z R
× × + +
= = -
× × + +
× × + +
EQUATION1284 V1 EN-US (Equation 196)
This means that the reach is reduced in reactive and resistive directions. If the real
and imaginary components of the constant A are equal to equation 197 and
equation 198.
Section 8 1MRK 506 369-UEN B
Impedance protection
272 Line distance protection REL670 2.2 IEC
Application manual
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