Parallel line out of service and not earthed
SEMOD168232-243 v3
Z0m
A B
Z< Z<
en05000223.vsd
IEC05000223 V1 EN-US
Figure 63: 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
63.
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 64: 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 37.
( )
( )
( )
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 37)
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 38 and
equation 39.
Section 8 1MRK 506 369-UEN B
Impedance protection
158 Line distance protection REL670 2.2 IEC
Application manual
To Next Page
Loading...
