ABB REL650 Applications Manual page 128

Section 6
Impedance protection
122
Maximum overreach will occur if the fault current infeed from remote line end is weak.
If considering a single phase-to-ground fault at 'p' unit of the line length from A to B on
the parallel line for the case when the fault current infeed from remote line end is zero, the
voltage V in the faulty phase at A side as in equation 43.
A
(
= × + ×
V p Z1 I K 3I
A L ph N 0
EQUATION1278 V3 EN
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 not grounded
A
Z0m
21
ANSI11000089 V1 EN
Figure 55: 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.
The line zero sequence mutual impedance does not influence the measurement of the
distance protection in a faulty circuit.
Ensure that the underreaching zones from both line ends will overlap a sufficient amount
(at least 10%) in the middle of the protected circuit.
)
+ ×
K 3I
Nm 0p
B
21
ANSI11000089_1_en.vsd
1MRK 506 334-UUS A
(Equation 43)
Application manual