ABB RELION 670 Series Applications Manual page 261

1MRK 504 152-UEN B
IEC09000250 V1 EN-US
Figure 141: Class 1, parallel line in service.
The equivalent zero sequence circuit of the lines can be simplified, see figure 142.
A
B
IEC09000253 V1 EN-US
Figure 142: 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 216.
=
U Z1
ph
EQUATION2312 V1 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.
If the current on the parallel line has negative sign compared to the current on the protected
line, that is, the current on the parallel line has an opposite direction compared to the current
on the protected line, the distance function will overreach. If the currents have the same
direction, the distance protection will underreach.
Maximum overreach will occur if the fault current infeed from remote line end is weak. If
considering a single phase-to-earth fault at 'p' unit of the line length from A to B on the parallel
line for the case when the fault current infeed from remote line end is zero, the voltage U
the faulty phase at A side as in equation 218.
Application manual
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
-
Z0 Z1
L L
ç
× + × +
I 3I 3I
L ph 0
è
×
3 Z1
L
216 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
Z0
m
÷
0p
ø
×
3 Z1
L
215 and after some simplification we can write the
ö
÷
ø
Section 7
Impedance protection
(Equation 216)
(Equation 217)
in
A
255