7.1.2.4 Voltage instability mitigation M13851-59 v3This setting is very much dependent on the power system characteristics, and thoroughstudies have to be made to find the suitable levels.7.1.2.5 Backup protection for power system faults M13851-62 v3The setting must be below the lowest occurring "normal" voltage and above the highestoccurring voltage during the fault conditions under consideration.7.1.2.6 Settings for Two step undervoltage protection M13851-65 v13The following settings can be done for Two step undervoltage protection UV2PTUV:ConnType: Sets whether the measurement shall be phase-to-earth fundamental value, phase-to-phase fundamental value, phase-to-earth RMS value or phase-to-phase RMS value.Operation:Off orOn.UBase (given inGlobalBaseSel): Base voltage phase-to-phase in primary kV. This voltage isused as reference for voltage setting. UV2PTUV measures selectively phase-to-earth voltages,or phase-to-phase voltage chosen by the settingConnType. The function will operate if thevoltage gets lower than the set percentage ofUBase. WhenConnType is set toPhN DFT orPhNRMS then the IED automatically divides set value forUBase by √3.UBase is used whenConnType is set toPhPh DFT orPhPh RMS. Therefore, always setUBase as rated primaryphase-to-phase voltage of the protected object. This means operation for phase-to-earthvoltage under:(%) ( )3U UBase kV< ×EQUATION1447 V1 EN-US (Equation 70)and operation for phase-to-phase voltage under:U (%) UBase(kV)< ×EQUATION1990 V1 EN-US (Equation 71)The below described setting parameters are identical for the two steps (n = 1 or 2). Therefore,the setting parameters are described only once.Characteristicn: This parameter gives the type of time delay to be used. The setting can beDefinite time,Inverse Curve A,Inverse Curve B,Prog. inv. curve. The selection is dependent onthe protection application.OpModen: This parameter describes how many of the three measured voltages that should bebelow the set level to give operation for step n. The setting can be1 out of 3,2 out of 3 or3 outof 3. In most applications, it is sufficient that one phase voltage is low to give operation. IfUV2PTUV shall be insensitive for single phase-to-earth faults,2 out of 3 can be chosen. Insubtransmission and transmission networks the undervoltage function is mainly a systemsupervision function and 3 out of 3 is selected.Un<: Set operate undervoltage operation value for stepn, given as % of the parameterUBase.The setting is highly dependent of the protection application. It is essential to consider theminimum voltage at non-faulted situations. Normally this voltage is larger than 90% ofnominal voltage.Section 7 1MRK 505 355-UEN AVoltage protection118Application manual
