ABB RET670 Applications Manual page 277

1MRK504116-UUS C
Application manual
When the parallel line is out of service and grounded at both ends on the bus bar side
of the line CT 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 119.
Z Z0
I
0
A
0
Z Z0
B
0
IEC99000039 V1 EN
Figure 120: 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 Z0-Z0m in parallel with (Z0-
Z0m)/Z0-Z0m+Z0m, which is equal to equation 185.
2 2
-
Z Z
0 om
=
Z
E
Z
0
EQUATION2002 V4 EN
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.
Parallel line out of service and not grounded
A
Z0m
21
ANSI11000089 V1 EN
Figure 121: Parallel line is out of service and not grounded.
m
Z0 m
m
99000039.vsd
B
21
ANSI11000089_1_en.vsd
Section 3
IED application
I
0
C
(Equation 185)
271