ABB RED670 Handbuch Seite 294

Abschnitt 4
IED Anwendung
290
æ
2
X
= · +
R R 1 0 m
ç
0 E 0
2 +
R X
è
0
DOCUMENT11520-IMG3502 V1 DE
æ
X
= · -
0 m
X X 1
ç
0 E 0
+
2
R
è
0
DOCUMENT11520-IMG3503 V1 DE
Parallel line out of service and not earthed
A
Z0m
Z<
IEC05000223 V1 DE
Abb. 154: 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
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.
I
0
A
B
IEC99000040 V1 DE
Abb. 155: 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 197.
ö
÷
2
ø
0
ö
2
÷
2
X
ø
0
B
Z<
en05000223.vsd
Z Z0
0 m
Z0
m
Z Z0
m
0
1MRK 505 186-UDE B
(Gleichung 195)
(Gleichung 196)
154
I
0
C
99000040.vsd
Applikationshandbuch