ABB RET670 - Page 307

Parallel line in service – Setting of zone1
With reference to section
"Parallel line applications", the zone reach can be set to 85%
of protected line.
Parallel line in service – setting of zone2
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
131 in section "Parallel line applications".
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 (Equation 220)
X
0E
X
0
X
m0
+=
EQUATION554 V1 EN (Equation 221)
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 (Equation 222)
If the denominator in equation 222 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
(Equation 223)
( )
( )
( ) ( )
2 2
0 Im
Im 0
Re Im
X m B
K
B B
×
=
+
EQUATION1428 V2 EN (Equation 224)
1MRK504116-UUS C Section 3
IED application
301
Application manual