ABB RET670 - Page 300

Here the equivalent zero sequence impedance is equal to Z0-Z0m in parallel with (Z0-
Z0m)/Z0-Z0m+Z0m which is equal to equation 207.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN (Equation 207)
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. All expressions below are proposed for
practical use. They assume the value of zero sequence, mutual resistance R0m equals
to zero. They consider only the zero-sequence, mutual reactance X0m. Calculate the
equivalent X0E and R0E zero-sequence parameters according to equation
208 and
equation 209 for each particular line section and use them for calculating the reach for
the underreaching zone.
2
0
0 0
2 2
0 0
1
m
E
X
R R
R X
æ ö
= · +
ç ÷
+
è ø
DOCUMENT11520-IMG3502 V1 EN (Equation 208)
2
0
0 0
2 2
0 0
1
m
E
X
X X
R X
æ ö
= · -
ç ÷
+
è ø
DOCUMENT11520-IMG3503 V1 EN (Equation 209)
Parallel line out of service and not grounded
Z0m
A B
Z< Z<
en05000223.vsd
IEC05000223 V1 EN
Figure 134: Parallel line is out of service and not grounded.
When the parallel line is out of service and not grounded, the zero sequence on that
line can only flow through the line admittance to the ground. The line admittance is
Section 3 1MRK504116-UUS C
IED application
294
Application manual