IEC09000164-2
Operate time
Current
tx
tnMin
IMinn
IEC09000164 V2 EN
Figure 52: Minimum operating current and operation time for inverse time
characteristics
In order to fully comply with curves definition setting parameter tnMin shall be set to
the value which is equal to the operate time of the selected inverse curve for measured
current of twenty times the set current pickup value. Note that the operating time value
is dependent on the selected setting value for time multiplier kn.
6.4.3.2 2nd harmonic restrain
2ndHarmStab: Operate level of 2nd harmonic current restrain set in % of the
fundamental current. The setting range is 5-100% in steps of 1%. Default setting is
20%.
HarmRestrainx: Enable block of step x from the harmonic restrain function (2nd
harmonic). This function should be used when there is a risk that power transformer
inrush currents might cause unwanted trip. Can be set Off or On.
OC4SPTOC function can be used in different ways, depending on the application
where the protection is used. A general description is given below.
The operate current setting inverse time protection or the lowest current step constant
inverse time protection must be given a current setting so that the highest possible load
current does not cause protection operation. Here consideration also has to be taken to
the protection reset current, so that a short peak of overcurrent does not cause
operation of the protection even when the overcurrent has ceased. This phenomenon
is described in figure
53.
Section 6 1MRK 505 291-UEN A
Current protection
108
Application manual
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