ABB RED650 - Page 125

Parallel line out of service and not earthed
GUID-949669D3-8B9F-4ECA-8F09-52A783A494E1 v2
Z
0m
A B
Z< Z<
IEC09000254_1_en.vsd
IEC09000254 V1 EN-US
Figure 59: 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
59
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
C
IEC09000255_1_en.vsd
I
0
I
0
Z
0m
Z
0
-
Z
0m
Z
0m
Z
0
-
IEC09000255 V1 EN-US
Figure 60: Equivalent zero-sequence impedance circuit for a double-circuit
line with one circuit disconnected and not earthed
The reduction of the reach is equal to equation 46.
( )
( )
( )
2
1 0
0
1 0
0
1 0
1
2
3
1
1
2 3
2
3
E f
m
U
f
f
Z Z R
Z
K
Z Z Z R
Z Z R
× × + +
= = -
× × + +
× × + +
EQUATION1284 V1 EN-US (Equation 46)
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 47 and
equation
48.
Re( ) 0 (2 1 0 3 ) 0 ( 0 2 1)
A R R R Rf X X X= × × + + × - × + ×
EQUATION1285 V1 EN-US
(Equation 47)
1MRK 505 393-UEN B Section 7
Impedance protection
Line differential protection RED650 2.2 IEC 119
Application manual