R R
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ +
+
DOCUMENT11520-IMG3502 V2 EN (Equation 120)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ −
+
DOCUMENT11520-IMG3503 V2 EN (Equation 121)
Parallel line out of service and not grounded
Z0m
A
OPEN
21
21
en05000223_ansi.vsd
CLOSED
OPEN
CLOSED
B
ANSI05000223 V1 EN
Figure 118: Parallel line is out of service and not grounded
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. 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 grounded at both ends.
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 237
Application manual
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