ABB REL650 series, Applications Manual

Page: 181 / 516

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 .
7.2.3.1 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
fB
. The calculation should be done using
the minimum source impedance values for Z
A
and the maximum source impedance values
for ZB in order to get the maximum through fault current from A to B.
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fB
Fault
ANSI10000277-1-en.vsd
ANSI10000277 V1 EN
Figure 82: Through fault current from A to B: I
fB
1MRK 506 334-UUS A
Section 7
Current protection
175
Application manual