ABB REG670 - Meshed Network with Parallel Line

The minimum primary setting (Is) for the instantaneous phase overcurrent protection
is then:
min
1.3
s
I I³ ×
EQUATION79 V3 EN (Equation 176)
The protection function can be used for the specific application only if this setting
value is equal to or less than the maximum fault current that the IED has to clear, I
F
in
Figure 170.
IEC09000024-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
IED
I
F
Fault
IEC09000024 V1 EN
Figure 170: Fault current: I
F
100
Is
IP
IBase
>>= ×
EQUATION1147 V3 EN
(Equation 177)
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 171, 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 171 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-earth and two-phase-to-earth
faults) is calculated.
Section 9 1MRK 502 071-UEN -
Current protection
322 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual