ABB RELION 670 Series Applications Manual page 214

Section 7
Impedance protection
Parallel line out of service and not earthed
A
Z<
IEC09000254 V1 EN-US
Figure 116: Parallel line is out of service and not earthed
When the parallel line is out of service and not earthed, the zero sequence on that line can only
flow through the line admittance to the earth. The line admittance is high which limits the
zero-sequence current on the parallel line to very low values. In practice, the equivalent zero-
sequence impedance circuit for faults at the remote bus bar can be simplified to the circuit
shown in figure
The line zero sequence mutual impedance does not influence the measurement of the distance
protection in a faulty circuit. This means that the reach of the underreaching distance
protection zone is reduced if, due to operating conditions, the equivalent zero sequence
impedance is set according to the conditions when the parallel system is out of operation and
earthed at both ends.
A
B
IEC09000255 V1 EN-US
Figure 117: Equivalent zero-sequence impedance circuit for a double-circuit line with one
The reduction of the reach is equal to equation 134.
=
K
U
EQUATION1284 V1 EN-US
This means that the reach is reduced in reactive and resistive directions. If the real and
imaginary components of the constant A are equal to equation
Re( ) A
EQUATION1285 V1 EN-US
Im( ) A
EQUATION1286 V1 EN-US
The real component of the KU factor is equal to equation 137.
208
B
Z
0m
Z<
IEC09000254_1_en.vsd
116
-
Z Z
0 0m
I
0
Z
0m
-
Z Z
0 0m
IEC09000255_1_en.vsd
circuit disconnected and not earthed
( )
1
× × + +
2 Z Z R
1 0 E f
3
( )
1
× × + +
2 Z Z R
1 0 f
3
= × × + + ×
R 0 (2 R 1 R 0 3
= × × + + ×
X (2 R R 3
0 1 0
I
0
C
2
Z
= -
1 m 0
(
× × + +
Z 2 Z Z
1 0
0
- × + ×
Rf ) X 0 ( 0 2 X
+ × × +
R ) R (2 X X
1 0 1 0
)
3 R
f
135 and equation 136.
X 1)
)
1MRK 504 152-UEN B
M17048-537 v5
(Equation 134)
(Equation 135)
(Equation 136)
Application manual