end, it is proportionally increased at the opposite line end. So this 15% reach reduction
does not significantly affect the operation of a permissive underreaching scheme.
Parallel line out of service and earthed
Z
0m
A
B
Z<
Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN
Figure 86:
The parallel line is out of service and earthed
When the parallel line is out of service and earthed 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
.
A
B
C
IEC09000252_1_en.vsd
I
0
I
0
Z
0m
Z
0
-
Z
0m
Z
0
-
Z
0m
IEC09000252 V1 EN
Figure 87:
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
2
2
0
0
om
E
Z
Z
Z
Z
-
=
EQUATION2002 V4 EN
(Equation 48)
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
for each particular line section
and use them for calculating the reach for the underreaching zone.
Section 8
1MRK 502 071-UEN -
Impedance protection
198
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Содержание Relion REG670
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