voltage is lower than the set blocking voltage in the preprocessing function, thefunction is blocked and no START or TRIP signal is issued.8.1.7.1 Measurement principleThe 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 in thepower system. If the voltage magnitude decreases below the setting MinValFreqMeasin the SMAI preprocessing function, which is described in the Basic IED Functionschapter and is set as a percentage of a global base voltage parameter, SAPTUF getsblocked, and the output BLKDMAGN is issued. All voltage settings are made inpercent of the setting of the global parameter UBase.To avoid oscillations of the output START signal, a hysteresis has been included.Frequency Comparatorf < StartFrequencySTARTSTARTTRIPBLOCKComparatorf > RestoreFreqBLOCKORDefiniteTimeDelayTimeDlyOperateTimeDlyRestore RESTORE100 msStart&TripOutputLogicIEC09000034-1.vsdTRIPBLKDMAGNfreqNotValidIEC09000034 V1 ENFigure 79: Simplified logic diagram for SAPTUF8.1.7.2 Time delayThe time delay for SAPTUF is a settable definite time delay, specified by the settingtDelay.Trip signal issuing requires that the under frequency condition continues for at leastthe user set time delay. If the START ceases during the delay time, and is not fulfilledagain within a defined reset time, the START output is reset.1MRK 511 287-UEN A Section 8Frequency protection181Technical manual
