ABB RELION RET670, Applications Manual

Page: 207 / 1016

R R
X
R X
E
m
0 0
0
2
0
2
0
2
1
= ⋅ +
+








DOCUMENT11520-IMG3502 V2 EN-US
(Equation 43)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1
= ⋅ −
+








DOCUMENT11520-IMG3503 V2 EN-US
(Equation 44)
Parallel line out of service and not grounded
SEMOD168232-243 v3
Z0m
A
OPEN
21
21
en05000223_ansi.vsd
CLOSED
OPEN
CLOSED
B
ANSI05000223 V1 EN-US
Figure 76: 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
76 .
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.
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 201
Application manual