Meshed Network With Parallel Line - ABB Relion REC670 Applications Manual

Section 7
Current protection
7.1.3.2

Meshed network with parallel line

In case of parallel lines, the influence of the induced current from the parallel line to the
protected line has to be considered. One example is given in figure
connected to the same busbars. In this case the influence of the induced fault current from the
faulty line (line 1) to the healthy line (line 2) is considered together with the two through fault
currents I
IED in figure
A fault in C has to be applied, and then the maximum current seen from the IED (I
healthy line (this applies for single-phase-to-earth and two-phase-to-earth faults) is
calculated.
~
IEC09000025 V1 EN-US
Figure 42: Two parallel lines. Influence from parallel line to the through fault current: I
The minimum theoretical current setting for the overcurrent protection function (Imin) will be:
³
Imin MAX I
EQUATION82 V1 EN-US
Where I
margins mentioned previously, the minimum setting (Is) for the instantaneous phase
overcurrent protection 3-phase output is then:
Is ³1.3·Imin
EQUATION83 V2 EN-US
The protection function can be used for the specific application only if this setting value is
equal or less than the maximum phase fault current that the IED has to clear.
The IED setting value
value for
>>=
IP
EQUATION1147 V3 EN-US
104
and I mentioned previously. The maximal influence from the parallel line for the
fA fB
42 will be with a fault at the C point with the C breaker open.
A C
Z
A
Fault
IED
, ,
( I I )
fA fB M
and I have been described in the previous paragraph. Considering the safety
fA fB
IP>> is given in percentage of the primary base current value, IBase . The
IP>> is given from this formula:
Is
×
100
IBase
Line 1
B
Z
L1
M
Z
L2
I
M
Line 2
42 where the two lines are
Z
~
B
IEC09000025-1-en.vsd
1MRK 511 358-UEN A
M12915-34 v6
) on the
M
M
(Equation 25)
(Equation 26)
(Equation 27)
Application manual