When the parallel line is out of service and grounded at both line ends on the bus bar
side of the line CTs 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 102.
A
B
C
IEC09000252_1_en.vsd
I
0
I
0
Z
0m
Z
0
-
Z
0m
Z
0
-
Z
0m
IEC09000252 V1 EN-US
Figure 102: 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 Z
0
-Z
0
m in parallel with (Z
0
-
Z
0m
)/Z
0
-Z
0m
+Z
0m
which is equal to equation
89.
EQUATION2002 V4 EN-US (Equation 89)
The influence on the distance measurement will be a considerable overreach, which
must be considered when calculating the settings. It is recommended to use a separate
setting group for this operation condition since it will reduce the reach considerably
when the line is in operation.
All expressions below are proposed for practical use. They assume the value of zero
sequence, mutual resistance R
0m
equals to zero. They consider only the zero sequence,
mutual reactance X
0m
. Calculate the equivalent X
0E
and R
0E
zero sequence parameters
according to equation
90 and equation 91 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-US (Equation 90)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ −
+
DOCUMENT11520-IMG3503 V2 EN-US (Equation 91)
Section 8 1MRK 502 071-UUS A
Impedance protection
240 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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