protections, they should have the same time delay characteristic. Therefore, a widerange of standardized inverse time characteristics are available for IEC and ANSI.It is also possible to tailor make the inverse time characteristic.Normally, it is required that the phase overcurrent protection shall reset as fast aspossible when the current level gets lower than the operation level. In some casessome sort of delayed reset is required. Therefore, different kinds of resetcharacteristics can be used.For some protection applications, there can be a need to change the current pick-uplevel for some time. A typical case is when the protection will measure the currentto a large motor. At the start up sequence of a motor the start current can besignificantly larger than the rated current of the motor. Therefore, there is apossibility to give a setting of a multiplication factor to the current pick-up level.This multiplication factor is activated from a binary input signal to the function.Power transformers can have a large inrush current, when being energized. Thisphenomenon is due to saturation of the transformer magnetic core during parts ofthe period. There is a risk that inrush current will reach levels above the pick-upcurrent of the phase overcurrent protection. The inrush current has a large 2ndharmonic content. This can be used to avoid unwanted operation of the protectionfunction. Therefore, OC4PTOC has a possibility of 2nd harmonic restrain if thelevel of 2nd harmonic current reaches a value above a set percent of thefundamental current.The phase overcurrent protection is often used as a protection for two and threephase short circuits. In some cases, it is not wanted to detect single-phase earthfaults by the phase overcurrent protection. This fault type is detected and clearedafter operation of earth fault protection. Therefore, it is possible to make a choicehow many phases, at minimum, that have to have current above the pick-up level,to enable operation. If set 1 of 3 it is sufficient to have high current in one phaseonly. If set 2 of 3 or 3 of 3 single-phase earth faults are not detected.8.2.3 Setting guidelines IP14982-1 v1M12982-4 v14When 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.The parameters for the directional phase overcurrent protection, four stepsOC4PTOC are set via the local HMI or PCM600.The following settings can be done for OC4PTOC.1MRK 505 393-UEN B Section 8Current protectionLine differential protection RED650 2.2 IEC 153Application manual
