percentage of a global base voltage parameter, SAPTUF gets blocked, and theoutput BLKDMAGN is issued. All voltage settings are made in percent of thesetting of the global parameter UBase.To avoid oscillations of the output START signal, a hysteresis has been included.9.1.7.2 Time delayThe time delay for SAPTUF is a settable definite time delay, specified by thesetting tDelay.Trip signal issuing requires that the under frequency condition continues for at leastthe user set time delay. If the START condition, with respect to the measuredfrequency ceases during the delay time, and is not fulfilled again within a definedreset time, the START output is reset.On the RESTORE output of SAPTUF a 100 ms pulse is issued, after a time delaycorresponding to the setting of tRestore, when the measured frequency returns tothe level corresponding to the setting RestoreFreq.9.1.7.3 BlockingIt is possible to block underfrequency protection SAPTUF completely, by binaryinput signal:BLOCK: blocks all outputsIf the measured voltage level decreases below the setting of MinValFreqMeas inthe preprocessing function, both the START and the TRIP outputs, are blocked.9.1.7.4 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 in thepower systems. When the frequency has returned back to the setting ofRestoreFreq, the RESTORE output is issued after the time delay tRestore. Thedesign of Under frequency protection SAPTUF is schematically described infigure 132.1MRK 502 034-UEN - Section 9Frequency protection257Technical Manual
