ABB RET670 - Page 186

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 52 in section "Parallel line in service".
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 79)
X
0E
X
0
X
m0
+=
EQUATION554 V1 EN (Equation 80)
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 81)
If the denominator in equation 81 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 82)
( )
( )
( ) ( )
2 2
0 Im
Im 0
Re Im
X m B
K
B B
×
=
+
EQUATION1428 V2 EN (Equation 83)
Parallel line is out of service and grounded in both ends
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-ground faults.
Section 3 1MRK504116-UUS C
IED application
180
Application manual