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Parallel line in service – Setting of zone1
SEMOD154704-50 v1
, the zone reach can be set to 85% of
protected line.
Parallel line in service – setting of zone2
SEMOD154704-53 v2
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-earth 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 229)
X
0E
X
0
X
m0
+
=
EQUATION554 V1 EN-US
(Equation 230)
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 231)
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 232)
( )
( )
( )
( )
2
2
0
Im
Im
0
Re
Im
X m
B
K
B
B
×
=
+
EQUATION1428 V2 EN-US
(Equation 233)
Parallel line is out of service and earthed in both ends
SEMOD154704-69 v3
Apply the same measures as in the case with a single set of setting parameters. This means
that an underreaching zone must not overreach the end of a protected circuit for the single
phase-to-earth faults. Set the values of the corresponding zone (zero-sequence resistance and
reactance) equal to:
R
0E
R
0
1
X
m0
2
R
0
2
X
0
2
+
--------------------------
+
è
ø
ç
÷
æ
ö
×
=
EQUATION561 V1 EN-US
(Equation 234)
1MRK 505 343-UEN B
Section 7
Impedance protection
257
Application manual
Summary of Contents for Relion 670 series
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