ABB RELION RET670 - Page 383

Z0m
A B
21 21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN-US
Figure 177: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure 178.
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 178: Equivalent zero sequence impedance circuit of the double-circuit,
parallel, operating line with a single phase-to-ground fault at the
remote busbar
When mutual coupling is introduced, the voltage at the relay point A will be changed
according to equation
267.
0 0
0
0 1
1 3 3
3 1 3 1
m
L L
ph p
ph L
L L
Z
Z Z
V Z I I I
Z Z
æ ö
-
= × + × +
ç ÷
× ×
è ø
EQUATION1276 V4 EN-US (Equation 267)
By dividing equation 267 by equation 266 and after some simplification we can write
the impedance present to the relay at A side as:
3 0
1 1
3 0
æ ö
×
= +
ç ÷
+ ×
è ø
L
I KNm
Z Z
I ph I KN
EQUATION1277 V3 EN-US (Equation 268)
Where:
KNm = Z0m/(3 · Z1L)
1MRK 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 377
Application manual