UMin = 90%UNom = 100%tMax = 1.0 stMin = 0.0 sExponent = 0, 1, 2, 3 and 490 95 10000.51en05000075.vsdTimeDlyOperate [s]U [% of UBase]Exponenent01234IEC05000075 V1 ENFigure 263: Voltage dependent inverse time characteristics for underfrequencyprotection SAPTUF. The time delay to operate is plotted as a functionof the measured voltage, for the Exponent = 0, 1, 2, 3, 4 respectively.10.1.7.4 BlockingIt is possible to block underfrequency protection SAPTUF partially or completely, bybinary input signals or by parameter settings, where:BLOCK: blocks all outputsBLKTRIP: blocks the TRIP outputBLKREST: blocks the RESTORE outputIf the measured voltage level decreases below the setting of MinValFreqMeas in thepreprocessing function both the START and the TRIP outputs are blocked.10.1.7.5 DesignThe 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. The timeintegrator can operate either due to a definite delay time or to the special voltagedependent delay time. When the frequency has returned back to the setting of1MRK502052-UEN B Section 10Frequency protection547Technical manual
