ABB RELION 670 SERIES Applications Manual page 327

1MRK 506 369-UUS -
Line distance protection REL670 2.2 ANSI
Application manual
Calculation for a 400 kV line, where we for simplicity have excluded the resistance, gives
with X1L=0.48 Ohm/Mile, X0L=1.4Ohms/Mile, zone 1 reach is set to 90% of the line
reactance p=71% that is, the protection is underreaching with approximately 20%.
The zero sequence mutual coupling can reduce the reach of distance protection on the
protected circuit when the parallel line is in normal operation. The reduction of the reach
is most pronounced with no current infeed in the IED closest to the fault. This reach
reduction is normally less than 15%. But when the reach is reduced at one line end, it is
proportionally increased at the opposite line end. So this 15% reach reduction does not
significantly affect the operation of a permissive underreaching scheme.
Parallel line out of service and grounded
A
OPEN
CLOSED
21
ANSI05000222 V1 EN
Figure 154: 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 117.
-
Z Z
0 0m
I
A
0
-
Z
Z
0
B 0m
IEC09000252 V1 EN
Figure 155: 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
Z )/Z -Z +Z which is equal to equation 119.
0m 0 0m 0m
B
OPEN
Z0m
CLOSED
21
en05000222_ansi.vsd
Z
0m
I
0
C
IEC09000252_1_en.vsd
Section 8
Impedance protection
-Z m in parallel with (Z
0 0
-
0
321