ABB RET670 - Page 332

Z0m
A B
21 21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN
Figure 143: Class 1, parallel line in service.
The equivalent zero sequence circuit of the lines can be simplified, see figure 52.
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN
Figure 144: 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 60.
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 V3 EN
(Equation 251)
By dividing equation 60 by equation 59 and after some simplification we can write the
impedance present to the relay at A side as:
3 0
1
3 0
t
I KNm
Z Z
I ph I KN
æ ö
×
= +
ç ÷
+ ×
è ø
EQUATION1277 V2 EN
(Equation 252)
Where:
KNm = Z0m/(3 · Z1L)
Section 3 1MRK504116-UUS C
IED application
326
Application manual