ABB RELION 670 Series Applications Manual page 263

1MRK 504 152-UEN B
I
A
B
IEC09000252 V1 EN-US
Figure 144: Equivalent zero sequence impedance circuit for the double-circuit line that
Here the equivalent zero sequence impedance is equal to Z
Z +Z
0m 0m
=
Z
E
EQUATION2002 V4 EN-US
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
X . Calculate the equivalent X
0m
and equation
underreaching zone.
R =
0 E
DOCUMENT11520-IMG3502 V2 EN-US
X =
0 E
DOCUMENT11520-IMG3503 V2 EN-US
Parallel line out of service and not earthed
A
Z<
IEC09000254 V1 EN-US
Figure 145: Parallel line is out of service and not earthed.
When the parallel line is out of service and not earthed, the zero sequence on that line can only
flow through the line admittance to the earth. The line admittance is high which limits the zero
sequence current on the parallel line to very low values. In practice, the equivalent zero
Application manual
-
Z Z
0 0m
0
Z
0m
-
Z
Z
0
0m
IEC09000252_1_en.vsd
operates with one circuit disconnected and earthed at both ends.
which is equal to equation 222.
2 2
-
Z Z
0 om
Z
0
equals to zero. They consider only the zero sequence, mutual reactance
0m
224 for each particular line section and use them for calculating the reach for the
2
 
X
0 m
R ⋅  1 + 
0
 
2 2
R + X
 
0 0
2
 
X
0 m
X ⋅  1 − 
0
 2 2 
R + X
 
0 0
B
Z
0m
Z<
IEC09000254_1_en.vsd
I
0
C
and R zero sequence parameters according to equation
0E 0E
Impedance protection
-Z m in parallel with (Z
0 0
GUID-0458F8AF-BDAC-4F07-B289-15B172FB39D9 v1
Section 7
-Z )/Z -
0 0m 0
(Equation 222)
223
(Equation 223)
(Equation 224)
257