ABB REL670 2.2 IEC - Page 349

When the parallel line is out of service and earthed 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
176.
A
B
C
IEC09000252_1_en.vsd
I
0
I
0
Z
0m
Z
0
-
Z
0m
Z
0
-
Z
0m
IEC09000252 V1 EN-US
Figure 176: Equivalent zero sequence impedance circuit for the double-circuit
line that operates with one circuit disconnected and earthed at both
ends
Here the equivalent zero-sequence impedance is equal to Z
0
-Z
0
m in parallel with
(Z
0
-Z
0m
)/Z
0
-Z
0m
+Z
0m
which is equal to equation 301.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN-US (Equation 301)
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 302 and equation 303 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 302)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ −
+








DOCUMENT11520-IMG3503 V2 EN-US (Equation 303)
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 343
Application manual