![background image](http://html1.mh-extra.com/html/abb/relion-670-series/relion-670-series_applications-manual_3052129315.webp)
Where:
Uph
is phase to earth voltage at the relay point
Iph
is phase current in the faulty phase
3I0
is earth fault current
Z1
is positive sequence impedance
Z0
is zero sequence impedance
Z
0m
A
B
Z<
Z<
IEC09000250_1_en.vsd
IEC09000250 V1 EN-US
Figure 189: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure
A
B
C
Z
0m
Z
0m
Z
0
-
Z
0m
Z
0
-
IEC09000253_1_en.vsd
IEC09000253 V1 EN-US
Figure 190: 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 relay point A will be changed according
0
0
0
0
1
1
3
3
3 1
3 1
m
L
L
ph
p
ph
L
L
L
Z
Z
Z
U
Z
I
I
I
Z
Z
æ
ö
-
=
×
+
×
+
ç
÷
×
×
è
ø
IECEQUATION1276 V3 EN-US
(Equation 318)
By dividing equation
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 319)
Where:
KNm
= Z0m/(3 · Z1L)
The second part in the parentheses is the error introduced to the measurement of the line
impedance.
1MRK 505 343-UEN B
Section 7
Impedance protection
309
Application manual
Summary of Contents for Relion 670 series
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