ABB RET670 - Page 283

Consider the possible enlarging factor that might exist due to fault infeed from adjacent
lines. Equation 190 can be used to calculate the reach in reverse direction when the
zone is used for blocking scheme, weak-end infeed, and so on.
Zrev 1.2 ZL-Z2rem³ ×
EQUATION1525 V4 EN (Equation 190)
Where:
ZL is the protected line impedance
Z2rem is zone 2 setting at remote end of protected line.
In some applications it might be necessary to consider the enlarging factor due to fault
current infeed from adjacent lines in the reverse direction in order to obtain certain
sensitivity.
Setting of zones for parallel line application
Parallel line in service – Setting of zone 1
With reference to section
"Parallel line application with mutual coupling", the zone
reach can be set to 85% of protected line.
Parallel line in service – Setting of zone 2
Overreaching zones (in general, zones 2 and 3) must overreach the protected circuit in
all cases. The greatest reduction of a reach occurs in cases when both parallel circuits
are in service with a single phase-to-ground fault located at the end of a protected line.
The equivalent zero-sequence impedance circuit for this case is equal to the one in
figure
118 in section "Parallel line application with mutual coupling".
The components of the zero-sequence impedance for the overreaching zones must be
equal to at least:
0 0
0
E m
R R R= +
EQUATION2009 V1 EN (Equation 191)
0 0
0
E m
X X X= +
EQUATION2010 V1 EN (Equation 192)
Check the reduction of a reach for the overreaching zones due to the effect of the zero-
sequence mutual coupling. The reach is reduced for a factor:
1MRK504116-UUS C Section 3
IED application
277
Application manual