ABB RELION RET670, Applications Manual

Page: 386 / 1016

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 sequence parameters
according to equation 274 and equation 275 for each particular line section and use
them for calculating the reach for the underreaching zone.
R R
X
R X
E
m
0 0
0
2
0
2
0
2
1
= ⋅ +
+








DOCUMENT11520-IMG3502 V2 EN-US
(Equation 274)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1
= ⋅ −
+








DOCUMENT11520-IMG3503 V2 EN-US
(Equation 275)
Parallel line out of service and not grounded
GUID-949669D3-8B9F-4ECA-8F09-52A783A494E1 v2
Z0m
A
OPEN
21
21
en05000223_ansi.vsd
CLOSED
OPEN
CLOSED
B
ANSI05000223 V1 EN-US
Figure 181: 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
high which limits the zero-sequence current on the parallel line to very low values. In
practice, the equivalent zero-sequence impedance circuit for faults at the remote bus
bar can be simplified to the circuit shown in figure
181
The line zero sequence mutual impedance does not influence the measurement of the
distance protection in a faulty circuit. This means that the reach of the underreaching
Section 8
1MRK 504 163-UUS A
Impedance protection
380 Transformer protection RET670 2.2 ANSI
Application manual