ABB RELION 670 Series Applications Manual page 157

1MRK 504 152-UEN B
Where:
Vph
Iph
3I0
Z1
Z0
IEC05000221 V1 EN-US
Figure 59: Class 1, parallel line in service
The equivalent circuit of the lines can be simplified, as shown in figure 60.
A
B
IEC99000038 V1 EN-US
Figure 60: Equivalent zero sequence impedance circuit of the double-circuit, parallel,
When mutual coupling is introduced, the voltage at the IED point A is changed, according to
equation 43.
=
V
ph
EQUATION1276 V4 EN-US
By dividing equation
impedance present to the IED at A side as:
=
Z Z
EQUATION1277 V3 EN-US
Where:
KNm
Application manual
is phase-to-earth voltage at the IED point
is phase current in the faulty phase
is earth-fault current
is positive sequence impedance
is zero sequence impedance
A
Z<
-
Z0
Z0
m
-
Z0
Z0
m
operating line with a single phase-to-earth-fault at the remote busbar
æ
Z 0
× + ×
Z 1 I 3 I L
ç
ph 0
L
×
3
è
43 by equation
æ
×
3 0 I KNm
+
1 1
ç
L
+ ×
I ph 3 0 I KN
è
= Z0m/(3 · Z1L)
B
Z0m
Z<
Z0 m
99000038.vsd
ö
-
Z 1 Z 0
+
L 3 I m
÷
0 p
×
Z 1 3 Z 1
ø
L L
42 and after some simplification we can write the
ö
÷
ø
Impedance protection
en05000221.vsd
C
(Equation 43)
(Equation 44)
Section 7
151