[ ]>pAt s B IxMulti Cin= + ×-æ öç ÷ç ÷ç ÷æ öç ÷ç ÷è øè øEQUATION1261 V2 EN-US (Equation 85)tPRCrvx,tTRCrvx,tCRCrvx: These parameters are used by the customer to create the inversereset time characteristic curve. For more information, refer toTechnical manual.HarmRestrainx: Enables the block of stepx from the harmonic restrain function (2ndharmonic). This function should be used when there is a risk of an unwanted trip caused bypower transformer inrush currents. It can be set toOff/On.8.2.3.2 2nd harmonic restrain M12982-91 v8If a power transformer is energized there is a risk that the transformer core will saturateduring part of the period, resulting in an inrush transformer current. This will give a decliningresidual current in the network, as the inrush current is deviating between the phases. There isa risk that the phase overcurrent function will give an unwanted trip. The inrush current has arelatively large ratio of 2nd harmonic component. This component can be used to create arestrain 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 harmonicrestrain signal, to block chosen steps. The setting is given in % of the fundamental frequencyresidual current. The setting range is5 - 100% in steps of 1%. The default setting is 20% andcan be used if a deeper investigation shows that no other value is needed..HarmRestrainx: This parameter can be setOff/On, to disable or enable the 2nd harmonicrestrain.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 givenbelow.The operating current setting of the inverse time protection, or the lowest current step of thedefinite time protection, must be defined so that the highest possible load current does notcause protection operation. Here consideration also has to be taken to the protection resetcurrent, so that a short peak of overcurrent does not cause operation of the protection evenwhen the overcurrent has ceased. This phenomenon is described in figure 74.Section 8 1MRK 505 363-UEN ACurrent protection136Application manual
