ABB Relion 670 series - Page 296

Parallel line out of service and not grounded
Z0m
A B
Z< Z<
en05000223.vsd
IEC05000223 V1 EN
Figure 143: Parallel line is out of service and not grounded.
When the parallel line is out of service and not grounded, the zero sequence on that line
can only flow through the line admittance to the ground. 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 143
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 144: 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 199.
( )
( )
( )
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 199)
Section 8 1MRK 506 369-UUS -
Impedance protection
290 Line distance protection REL670 2.2 ANSI
Application manual