ABB RELION 670 Series Applications Manual page 211

1MRK 504 152-UEN B
Where:
Uph
Iph
3I0
Z1
Z0
IEC09000250 V1 EN-US
Figure 112: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, see figure 113.
A
B
IEC09000253 V1 EN-US
Figure 113: Equivalent zero sequence impedance circuit of the double-circuit, parallel,
When mutual coupling is introduced, the voltage at the relay point A will be changed according
to equation 125.
=
U Z
ph
IECEQUATION1276 V3 EN-US
By dividing equation
impedance present to the relay at A side as:
=
Z Z
EQUATION1277 V3 EN-US
Where:
KNm
The second part in the parentheses is the error introduced to the measurement of the line
impedance.
Application manual
is phase to earth voltage at the relay point
is phase current in the faulty phase
is earth fault current
is positive sequence impedance
is zero sequence impedance
A
Z
0m
Z<
-
Z
Z
0 0m
-
Z
Z
0
0m
operating line with a single phase-to-earth fault at the remote busbar
æ
-
Z 0 Z 1
× + ×
1 I 3 I L L
ç
ph 0
L
×
3 Z 1
è
L
125 by equation
æ
×
3 0 I KNm
+
1 1
ç
L
+ ×
I ph 3 0 I KN
è
= Z0m/(3 · Z1L)
B
Z<
IEC09000250_1_en.vsd
Z
0m
C
IEC09000253_1_en.vsd
ö
Z 0
+
3 I m
÷
0 p
×
3 Z 1
ø
L
124 and after some simplification we can write the
ö
÷
ø
Section 7
Impedance protection
(Equation 125)
(Equation 126)
205