ABB RET670 Applications Manual page 178

Section 3
IED application
172
A
OPEN
CLOSED
21
ANSI05000222 V1 EN
Figure 53: The parallel line is out of service and grounded
When the parallel line is out of service and grounded 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 54.
-
Z Z
0 0m
I
A
0
-
Z
Z
0 0m
B
IEC09000252 V1 EN
Figure 54: 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 Z
of (Z -Z ) and Z which is equal to equation 66.
0 0m 0m
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.
All expressions below are proposed for practical use. They assume the value of zero
sequence, mutual resistance R
mutual reactance X . Calculate the equivalent X
0m
according to equation 67
for calculating the reach for the underreaching zone.
B
OPEN
Z0m
CLOSED
21
en05000222_ansi.vsd
Z
0m
I
0
C
IEC09000252_1_en.vsd
equals to zero. They consider only the zero sequence,
0m
and equation 68 for each particular line section and use them
1MRK504116-UUS C
-Z m in series with parallel
0 0
and R zero sequence parameters
0E 0E
Application manual
(Equation 66)