ABB RET670 - Page 301

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 134
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 grounded 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
Figure 135: Equivalent zero-sequence impedance circuit for a double-circuit line
with one circuit disconnected and not grounded.
The reduction of the reach is equal to equation 210.
( )
( )
( )
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 (Equation 210)
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 211 and equation 212.
Re( ) 0 (2 1 0 3 ) 0 ( 0 2 1)
A R R R Rf X X X= × × + + × - × + ×
EQUATION1285 V1 EN
(Equation 211)
0 1 0 1 0 1 0
Im( ) (2 3 ) (2 )A X R R R R X X= × × + + × + × × +
EQUATION1286 V1 EN (Equation 212)
The real component of the KU factor is equal to equation 213.
1MRK504116-UUS C Section 3
IED application
295
Application manual