Z
Z
0
m0
Z
Z
0
m0
Zm0
A
B
C
99000039.vsd
I
0
I
0
DOCUMENT11520-IMG7100 V1 EN-US
Figure 156: 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 Z0-Z0m in parallel with (Z0-
Z0m)/Z0-Z0m+Z0m which is equal to equation
2
2
0
0
om
E
Z
Z
Z
Z
-
=
EQUATION2002 V4 EN-US
(Equation 216)
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
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 217)
X
X
X
R
X
E
m
0
0
0
2
0
2
0
2
1
=
⋅
−
+
DOCUMENT11520-IMG3503 V2 EN-US
(Equation 218)
Parallel line out of service and not earthed
SEMOD154680-242 v2
Z0m
A
B
Z<
Z<
en05000223.vsd
IEC05000223 V1 EN-US
Figure 157: Parallel line is out of service and not earthed.
1MRK 505 343-UEN B
Section 7
Impedance protection
251
Application manual
Содержание Relion 670 series
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