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.
2ndHarmStab: The rate of 2nd harmonic current content for activation of the 2nd
harmonic restrain signal, to block chosen steps. The setting is given in % of the
fundamental frequency residual current. The setting range is 5 - 100% in steps of 1%.
The default setting is 20% and can be used if a deeper investigation shows that no other
value is needed..
HarmRestrainx: This parameter can be set Disabled/Enabled, to disable or enable the
2nd harmonic restrain.
The four step phase overcurrent protection 3-phase output can be used in different
ways, depending on the application where the protection is used. A general description
is given below.
The pickup 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
185.
Section 3 1MRK504116-UUS C
IED application
408
Application manual
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