6.1.3 Setting guidelines
The parameters for instantaneous phase overcurrent protection 3-phase output
PHPIOC are set via the local HMI or PCM600.
This protection function must operate only in a selective way. So check all system and
transient conditions that could cause its unwanted operation.
Only 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.
GlobalBaseSel: Selects the global base value group used by the function to define
(IBase), (UBase) and (SBase).
IP>>: Set operate current in % of IBase.
6.1.3.1 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 38, 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 Z
B
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
IEC09000022-1-en.vsd
IEC09000022 V1 EN
Figure 38: Through fault current from A to B: I
fB
Section 6 1MRK 505 291-UEN A
Current protection
86
Application manual
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