Z0m
A B
21 21
en05000221_ansi.vsd
FAULT
ANSI05000221 V1 EN
Figure 61: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, as shown in figure 62.
A
B
C
Z0
m
Z0
Z0
m
-
Z0
Z0
m
-
99000038.vsd
IEC99000038 V1 EN
Figure 62: 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
31.
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 (Equation 31)
By dividing equation 31 by equation 30 and after some simplification we can write the
impedance present to the IED 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
(Equation 32)
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 165
Application manual
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