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 169: Equivalent zero sequence impedance circuit for the double-circuit line that
operates with one circuit disconnected and earthed 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
.
2
2
0
0
om
E
Z
Z
Z
Z
-
=
EQUATION2002 V4 EN-US
(Equation 266)
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
and equation
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 267)
X
X
X
R
X
E
m
0
0
0
2
0
2
0
2
1
=
⋅
−
+
DOCUMENT11520-IMG3503 V2 EN-US
(Equation 268)
Parallel line out of service and not earthed
GUID-0458F8AF-BDAC-4F07-B289-15B172FB39D9 v1
Z
0m
A
B
Z<
Z<
IEC09000254_1_en.vsd
IEC09000254 V1 EN-US
Figure 170: 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
Section 7
1MRK 505 343-UEN B
Impedance protection
276
Application manual
Содержание Relion 670 series
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