Meshed Network Without Parallel Line - ABB REQ650 Applications Manual

1MRK 505 291-UEN A
6.2.3.1
Application manual
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-earth
and two-phase-to-earth 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
UBase) 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.
IP>>: 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 earth
and two-phase-to-earth faults. With reference to figure 42, apply a fault in B and then
calculate the current through fault phase current I
using the minimum source impedance values for Z
impedance values for ZB in order to get the maximum through fault current from A to
B.
A
Z
~
A
IED
IEC10000277 V1 EN
Figure 42: Through fault current from A to B: I
Then a fault in A has to be applied and the through fault current I
figure 43. In order to get the maximum through fault current, the minimum value for
Z and the maximum value for Z
B
. The calculation should be done
fB
and the maximum source
A
I
fB
B
Z Z
L
Fault
fB
have to be considered.
A
Section 6
Current protection
~
B
IEC10000277-1-en.vsd
has to be calculated,
fA
91