From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation
.
ph
ph
0
1
ph
N
ph
0
1
0
V
V
Z
Z
I
3
K
I
3I
3 Z
I
Z
=
=
-
+
×
+
×
×
EQUATION1275 V3 EN-US
(Equation 117)
Where:
Vph
is phase to ground voltage at the relay point
Iph
is phase current in the faulty phase
3I0
is ground fault current
Z1
is positive sequence impedance
Z0
is zero sequence impedance
Z0m
A
B
21
21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN-US
Figure 125:
Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure
.
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 126:
Equivalent zero sequence impedance circuit of the double-circuit,
parallel, operating line with a single phase-to-ground fault at the
remote busbar
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI
267
Application manual
Содержание RELION RET670
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