When the parallel line is out of service and grounded at both ends on the bus bar side of
the line CT so that zero sequence current can flow on the parallel line, the equivalent zero
sequence circuit of the parallel lines will be according to figure 141.
Z Z
0 m0
Z Z
0 m0
Z
m0
A
B
C
99000039.vsd
I
0
I
0
DOCUMENT11520-IMG7100 V1 EN
Figure 142: Equivalent zero-sequence impedance circuit for the double-circuit line
that operates with one circuit disconnected and grounded at both ends.
Here the equivalent zero sequence impedance is equal to Z0-Z0m in parallel with (Z0-
Z0m)/Z0-Z0m+Z0m which is equal to equation 196.
EQUATION2002 V4 EN (Equation 196)
The influence on the distance measurement will be a considerable overreach, which must
be considered when calculating the settings. It is a recommendation to use a separate
setting group for this operation condition since it will reduce the reach considerable when
the line is in operation. All expressions below are proposed for practical use. They assume
the value of zero sequence, mutual resistance R0m equals to zero. They consider only the
zero-sequence, mutual reactance X0m. Calculate the equivalent X0E and R0E zero-
sequence parameters according to equation
197 and equation 198 for each particular line
section and use them for calculating the reach for the underreaching zone.
R R
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ +
+
DOCUMENT11520-IMG3502 V2 EN (Equation 197)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ −
+
DOCUMENT11520-IMG3503 V2 EN (Equation 198)
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 289
Application manual
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