9.1.3.2 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 254, where the two
lines are 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
fA
and I
fB
mentioned previously. The maximal influence
from the parallel line for the IED in Figure
254 will be with a fault at the C point with the
C breaker open.
A fault in C has to be applied, and then the maximum current seen from the IED (I
M
) on
the healthy line (this applies for single-phase-to-ground and two-phase-to-ground faults)
is calculated.
~ ~
Z
A
Z
B
Z
L1
A B
I
M
Fault
IED
Z
L2
M
C
Line 1
Line 2
ANSI09000025_2_en.vsd
ANSI09000025 V2 EN
Figure 254: Two parallel lines. Influence from parallel line to the through fault current:
I
M
The minimum theoretical current setting for the overcurrent protection function (Imin)
will be:
EQUATION82 V1 EN
(Equation 446)
Where I
fA
and I
fB
have been described in the previous paragraph. Considering the safety
margins mentioned previously, the minimum setting (Is) for the instantaneous phase
overcurrent protection 3-phase output is then:
EQUATION83 V2 EN (Equation 447)
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 491
Application manual
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