HarmRestrainx: Enable block of step x from the harmonic restrain function (2ndharmonic). This function should be used when there is a risk if power transformerinrush currents might cause unwanted trip. Can be set Off/On.tPCrvx, tACrvx, tBCrvx, tCCrvx: Parameters for customer creation of inverse timecharacteristic curve (Curve type = 17). See equation 30 for the time characteristicequation.[ ]>pAt s B IxMulti Cin= + ×-æ öç ÷ç ÷ç ÷æ öç ÷ç ÷è øè øEQUATION1261 V2 EN-US (Equation 30)For more information, please refer to the “Technical reference manual”.tPRCrvx, tTRCrvx, tCRCrvx: Parameters for customer creation of inverse reset timecharacteristic curve (Reset Curve type = 3). Further description can be found in the“Technical reference manual”.7.2.3.2 Second harmonic restrain SEMOD127941-90 v1If 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 adeclining residual current in the network, as the inrush current is deviating between thephases. There is a risk that the phase overcurrent function will give an unwanted trip.The inrush current has a relatively large ratio of 2nd harmonic component. Thiscomponent 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 second harmonic current content for activation of the 2ndharmonic restrain signal, to block chosen steps. The setting is given in % of thefundamental frequency residual current. The setting range is 5-100% in step of 1%.The default setting is 20%.HarmRestrainx: This parameter can be set Off/On, disable or enable the 2nd harmonicrestrain.The four-step phase overcurrent protection can be used in different ways, depending onthe application where the protection is used. A general description is given below.The pick up current setting inverse time protection or the lowest current step constantinverse time protection must be given a current setting so that the highest possible load1MRK 505 370-UUS A Section 7Current protectionBusbar protection REB670 2.2 ANSI 191Application manual
