ABB RET670 - Page 203

Z0m
A B
21 21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN
Figure 64: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, as shown in figure 65.
A
B
C
Z0
m
Z0
Z0
m
-
Z0
Z0
m
-
99000038.vsd
IEC99000038 V1 EN
Figure 65: 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 IED point A is changed,
according to equation 105.
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 105)
By dividing equation 105 by equation 104 and after some simplification we can write
the impedance present to the IED 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 106)
1MRK504116-UUS C Section 3
IED application
197
Application manual