10.1.3.6 Settings for two step undervoltage protection M13851-65 v14The following settings can be done for Two step undervoltage protectionUV2PTUV:ConnType: Sets whether the measurement shall be phase-to-earth fundamentalvalue, phase-to-phase fundamental value, phase-to-earth RMS value or phase-to-phase RMS value.Operation: Off or On.UBase (given in GlobalBaseSel): Base voltage phase-to-phase in primary kV. Thisvoltage is used as reference for voltage setting. UV2PTUV will operate if thevoltage becomes lower than the set percentage of UBase. This setting is used whenConnType is set to PhPh DFT or PhPh RMS. Therefore, always set UBase as ratedprimary phase-to-phase voltage of the protected object. For more information, referto the Technical manual.The setting parameters described below 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 settingcan be Definite time, Inverse Curve A, Inverse Curve B, Prog. inv. curve. Theselection is dependent on the protection application.OpModen: This parameter describes how many of the three measured voltagesshould be below the set level to give operation for step n. The setting can be 1 outof 3, 2 out of 3 or 3 out of 3. In most applications, it is sufficient that one phasevoltage is low to give operation. If UV2PTUV shall be insensitive for single phase-to-earth faults, 2 out of 3 can be chosen. In subtransmission and transmissionnetworks the undervoltage function is mainly a system supervision function and 3out of 3 is selected.Un<: Set operate undervoltage operation value for step n, given as % of theparameter UBase. The setting is highly dependent on the protection application. Itis essential to consider the minimum voltage at non-faulted situations. Normally,this non-faulted voltage is larger than 90% of the nominal voltage.tn: time delay of step n, given in s. This setting is dependent on the protectionapplication. In many applications the protection function shall not directly tripwhen there is a short circuit or earth faults in the system. The time delay must becoordinated to the other short circuit protections.tResetn: Reset time for step n if definite time delay is used, given in s. The defaultvalue is 25 ms.tnMin: Minimum operation time for inverse time characteristic for step n, given ins. When using inverse time characteristic for the undervoltage function during verylow voltages can give a short operation time. This might lead to unselectivetripping. By setting t1Min longer than the operation time for other protections, suchunselective tripping can be avoided.1MRK 506 369-UEN B Section 10Voltage protectionLine distance protection REL670 2.2 IEC 535Application manual
