tnMin: Minimum operate time for all inverse time characteristics. At high currents the
inverse time characteristic might give a very short operation time. By setting this
parameter the operation time of the step can never be shorter than the setting. Setting
range: 0.000 - 60.000s in steps of 0.001s.
IEC09000164-2
Operate time
Current
tx
tnMin
IMinn
IEC09000164 V2 EN
Figure 47: Minimum operate 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 operating 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.
HarmRestrainx: Enable block of step n from the harmonic restrain function (2nd
harmonic). This function should be used when there is a risk if power transformer
inrush currents might cause unwanted trip. Can be set Off/On.
6.3.3.2 2nd harmonic restrain
If a power transformer is energized there is a risk that the transformer core will saturate
during part of the period, resulting in an inrush transformer current. This will give a
declining residual current in the network, as the inrush current is deviating between
the phases. There is a risk that the phase overcurrent function will give an unwanted
trip. The inrush current has a relatively large ratio of 2
nd
harmonic component. This
component can be used to create a restrain signal to prevent this unwanted function.
The settings for the 2nd harmonic restrain are described below.
Section 6 1MRK 505 291-UEN A
Current protection
98
Application manual
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