Curve nameANSI Long Time Extremely InverseANSI Long Time Very InverseANSI Long Time InverseIEC Normal InverseIEC Very InverseIEC InverseIEC Extremely InverseIEC Short Time InverseIEC Long Time InverseIEC Definite TimeASEA RIRXIDG (logarithmic)Power transformers can have a large inrush current, when being energized. This inrushcurrent can have residual current components. The phenomenon is due to saturation of thetransformer magnetic core during parts of the cycle. There is a risk that inrush current willgive a residual current that reaches level above the pickup current of the residualovercurrent protection. The inrush current has a large second harmonic content. This canbe used to avoid unwanted operation of the protection. Therefore, EF4PTOC (51N_67N)has a possibility of second harmonic restrain 2ndHarmStab if the level of this harmoniccurrent reaches a value above a set percentage of the fundamental current.7.6.3 Setting guidelinesWhen inverse time overcurrent characteristic is selected, the operate timeof the stage will be the sum of the inverse time delay and the set definitetime delay. Thus, if only the inverse time delay is required, it is importantto set the definite time delay for that stage to zero.The parameters for the four step residual overcurrent protection, zero or negativesequence direction EF4PTOC (51N/67N) are set via the local HMI or PCM600.The following settings can be done for the four step residual overcurrent protection.GlobalBaseSel: Selects the global base value group used by the function to define (IBase),(VBase) and (SBase).SeqTypeUPol: It is used to select type of voltage polarization quantity, i.e. ZeroSeq andNegSeq for direction detection.Section 7 1MRK 506 334-UUS ACurrent protection204Application manual
