Where:
Vph
is phase-to-earth voltage at the IED point
Iph
is phase current in the faulty phase
3I0
is earth-fault current
Z1
is positive sequence impedance
Z0
is zero sequence impedance
Z0m
A
B
Z<
Z<
en05000221.vsd
IEC05000221 V1 EN-US
Figure 74: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, as shown in figure
.
A
B
C
Z0m
Z0
Z0
m
-
Z0
Z0
m
-
99000038.vsd
IEC99000038 V1 EN-US
Figure 75: Equivalent zero sequence impedance circuit of the double-circuit, parallel,
operating line with a single phase-to-earth-fault at the remote busbar
When mutual coupling is introduced, the voltage at the IED point A is changed, according to
.
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 49)
By dividing equation
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-US
(Equation 50)
Where:
KNm
= Z0m/(3 · Z1L)
1MRK 505 343-UEN B
Section 7
Impedance protection
151
Application manual
Summary of Contents for Relion 670 series
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