ABB REL670 2.2 IEC - Page 375

This reach reduction is normally less than 15%. But when the reach is reduced at
one line 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
GUID-DFB5C5AD-407D-4325-BE46-092F5F5D2F59 v1GUID-A93E0062-A4E1-447B-A3A3-74B49581AD70 v1
Z
0m
A B
Z< Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN-US
Figure 190: 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
191.
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 191: 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 347.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN-US
(Equation 347)
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
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 369
Application manual