Meshed Network Without Parallel Line - ABB REL650 Applications Manual

1MRK 506 334-UUS A
7.2.3.1
Application manual
This protection function must operate only in a selective way. So check all system and
transient conditions that could cause its unwanted operation.
Detailed network studies can determine the operating conditions under which the highest
possible fault current is expected on the line . In most cases, this current appears during
three-phase fault conditions. But also examine single-phase-to-ground and two-phase-to-
ground conditions.
Also, study transients that could cause a high increase of the line current for short times.
A typical example is a transmission line with a power transformer at the remote end, which
can cause high inrush current when connected to the network and can thus also cause the
operation of the built-in, instantaneous, overcurrent protection.
Common base IED values for primary current (IBase), primary voltage (setting VBase)
and primary power (SBase) are set in a Global base values for settings function
GBASVAL. Setting GlobalBaseSel is used to select a GBASVAL function for reference
of base values.
Pickup: Set operate current in % of IBase.

Meshed network without parallel line

The following fault calculations have to be done for three-phase, single-phase-to ground
and two-phase-to-ground faults. With reference to figure 82, apply a fault in B and then
calculate the current through fault phase current I
the minimum source impedance values for Z
for ZB in order to get the maximum through fault current from A to B.
A
Z
~
A
IED
ANSI10000277 V1 EN
Figure 82: Through fault current from A to B: I
. The calculation should be done using
fB
and the maximum source impedance values
A
I
fB
B
Z Z
L B
Fault
fB
Section 7
Current protection
~
ANSI10000277-1-en.vsd
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