In many 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.
8.12.3.5
Setting of zones for parallel line application
GUID-4E0C3824-41B6-410F-A10E-AB9C3BFE9B12 v1
Parallel line in service – Setting of zone 1
GUID-8A62367C-2636-4EC1-90FF-397A51F586F7 v1
, the zone reach can be set to 85%
of the protected line.
However, influence of mutual impedance has to be taken into account.
Parallel line in service – setting of zone 2
GUID-98D11A72-C5BE-4C67-ADB5-95124C2AF987 v1
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
The components of the zero sequence impedance for the overreaching zones must be
equal to at least:
R
0E
R
0
R
m0
+
=
EQUATION553 V1 EN-US
(Equation 286)
X
0E
X
0
X
m0
+
=
EQUATION554 V1 EN-US
(Equation 287)
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:
0
0 1
2 1
0
m
f
Z
K
Z
Z
R
= -
×
+
+
EQUATION1426 V1 EN-US
(Equation 288)
If the denominator in equation
is called B and Z0m is simplified to X0m, then the
real and imaginary part of the reach reduction factor for the overreaching zones can be
written as:
( )
( )
( )
( )
2
2
0
Re
Re
0
1
Re
Im
X m
B
K
B
B
×
= -
+
EQUATION1427 V2 EN-US
(Equation 289)
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI
387
Application manual
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