ABB REL670 2.2 IEC - Page 227

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 earthed
M17048-477 v3M17048-479 v7
Z
0m
A B
Z< Z<
IEC09000251_1_en.vsd
IEC09000251 V1 EN-US
Figure 114: The parallel line is out of service and earthed
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
115.
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 115: 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 series with
parallel of (Z
0
-Z
0m
) and Z
0m
which is equal to equation
116.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN-US
(Equation 116)
The influence on the distance measurement will be a considerable overreach, which
must be considered when calculating the settings.
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
117 and equation 118 for each
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 221
Application manual