ABB Relion 670 series, Applications Manual

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Parallel line out of service and not earthed
SEMOD168232-243 v3
Z0m
A B
Z< Z<
en05000223.vsd
IEC05000223 V1 EN-US
Figure 78: Parallel line is out of service and not earthed
When the parallel line is out of service and not earthed, the zero sequence on that line can only
flow through the line admittance to the earth. The line admittance is high which limits the zero
sequence current on the parallel line to very low values. In practice, the equivalent zero
sequence impedance circuit for faults at the remote bus bar can be simplified to the circuit
shown in figure 78 .
The line zero-sequence mutual impedance does not influence the measurement of the distance
protection in a faulty circuit. This means that the reach of the underreaching distance
protection zone is reduced if, due to operating conditions, the equivalent zero sequence
impedance is set according to the conditions when the parallel system is out of operation and
earthed at both ends.
Z Z0
0 m
Z Z0
0
m
Z0
m
A
B
C
99000040.vsd
I
0
I
0
IEC99000040 V1 EN-US
Figure 79: Equivalent zero-sequence impedance circuit for a double-circuit line with one
circuit disconnected and not earthed
The reduction of the reach is equal to equation 58 .
( )
( )
( )
2
1 0
0
1 0
0
1 0
1
2
3
1
1
2 3
2
3
E f
m
U
f
f
Z Z R
Z
K
Z Z Z R
Z Z R
× × + +
= = -
× × + +
× × + +
EQUATION1284 V1 EN-US
(Equation 58)
This means that the reach is reduced in reactive and resistive directions. If the real and
imaginary components of the constant A are equal to equation 59 and equation 60 .
Re( ) 0 (2 1 0 3 ) 0 ( 0 2 1) A R R R Rf X X X
= × × + + × - × + ×
EQUATION1285 V1 EN-US
(Equation 59)
0 1 0 1 0 1 0
Im( ) (2 3 ) (2 ) A X R R R R X X
= × × + + × + × × +
EQUATION1286 V1 EN-US
(Equation 60)
Section 7 1MRK 505 343-UEN B
Impedance protection
154
Application manual