ABB RET670 - Page 178

Z0m
A B
21
21
en05000222_ansi.vsd
CLOSED
CLOSED
OPEN OPEN
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.
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 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
0
-Z
0
m in series with parallel
of (Z
0
-Z
0m
) and Z
0m
which is equal to equation 66.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN
(Equation 66)
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
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
67 and equation 68 for each particular line section and use them
for calculating the reach for the underreaching zone.
Section 3 1MRK504116-UUS C
IED application
172
Application manual