ABB RELION RET670, Applications Manual

Page: 337 / 1016

Z0m
A B
21 21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN-US
Figure 154: Class 1, parallel line in service.
The equivalent zero sequence circuit of the lines can be simplified, see figure 155 .
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 155: 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
209 .
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 209)
By dividing equation 209 by equation 208 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 210)
Where:
KNm = Z0m/(3 · Z1L)
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 331
Application manual