Curve nameANSI Long Time InverseIEC Normal InverseIEC Very InverseIEC InverseIEC Extremely InverseIEC Short Time InverseIEC Long Time InverseIEC Definite TimeUser ProgrammableASEA RIRXIDG or RD (logarithmic)It is also possible to tailor make the inverse time characteristic.Normally it is required that EF4PTOC shall reset as fast as possible when thecurrent level gets lower than the operation level. In some cases some sort ofdelayed reset is required. Therefore different kinds of reset characteristics can beused.For some protection applications, there can be a need to change the currentoperating level for some time. Therefore, there is a possibility to give a setting of amultiplication factor INxMult to the residual current pick-up level. Thismultiplication factor is activated from a binary input signal ENMULTx to thefunction.Power transformers can have a large inrush current, when being energized. Thisinrush current can produce residual current component. The phenomenon is due tosaturation of the transformer magnetic core during parts of the cycle. There is a riskthat inrush current will give a residual current that reaches level above theoperating current of the residual overcurrent protection. The inrush current has alarge second harmonic content. This can be used to avoid unwanted operation ofthe protection. Therefore, EF4PTOC has a possibility of second harmonic restrainif the level of 2nd harmonic current reaches a value above a set percent of thefundamental current.7.4.3 Setting guidelines IP14988-1 v1M15282-3 v11When inverse time overcurrent characteristic is selected, theoperate time of the stage will be the sum of the inverse time delayand the set definite time delay. Thus, if only the inverse time delayis required, it is important to set the definite time delay for thatstage to zero.Section 7 1MRK 504 169-UEN ACurrent protection122 Transformer protection RET650 2.2 IECApplication manual
