90 95 10000.51en05000075.vsdTimeDlyOperate [s]U [% of UBase]Exponenent01234IEC05000075 V1 EN-USFigure 127: Voltage dependent inverse time characteristics for underfrequencyprotection SAPTUF. The time delay to operate is plotted as afunction of the measured voltage, for the Exponent = 0, 1, 2, 3, 4respectively.10.1.6.4 Blocking M13354-50 v7It is possible to block underfrequency protection SAPTUF partially or completely,by binary input signals or by parameter settings, where:BLOCK: blocks the START, TRIP andRESTORE outputsBLKTRIP: blocks the TRIP outputBLKREST: blocks the RESTORE outputIf the measured voltage level decreases below the setting of IntBlockLevel, both theSTART and the TRIP outputs are blocked.10.1.6.5 Design M13354-63 v10The frequency measuring element continuously measures the frequency of thepositive sequence voltage and compares it to the setting StartFrequency. Thefrequency signal is filtered to avoid transients due to switchings and faults. Thetime integrator can operate either due to a definite delay time or to the specialvoltage dependent delay time. When the frequency has returned back to the settingof RestoreFreq, the RESTORE output is issued after the time delay tRestore. Thedesign of underfrequency protection SAPTUF is schematically described infigure 128.1MRK 505 394-UEN A Section 10Frequency protectionLine differential protection RED650 2.2 IEC 271Technical manual
