ABB RELION RET670 Applications Manual page 273

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 117.
V V
ph
Z = =
I
- +
Z Z I 3
0 1 ph
+ ×
I 3I
ph 0
×
3 Z
1
EQUATION1275 V3 EN-US
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
A
21
ANSI05000221 V1 EN-US
Figure 125: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure 126.
-
Z
Z
0
0m
A
-
Z
Z
0
0m
B
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
ph
×
K
N
0
FAULT
Z0m
Z
0m
IEC09000253_1_en.vsd
Section 8
Impedance protection
B
21
en05000221_ansi.vsd
C
(Equation 117)
267