Table 139:SAPTUF Non group settings (basic)Name Values (Range) Unit Step Default DescriptionGlobalBaseSel 1 - 12 - 1 1 Selection of one of the Global BaseValue groups10.1.6 Operation principle M13354-3 v9Underfrequency protection SAPTUF is used to detect low power system frequency.SAPTUF can either have a definite time delay or a voltage magnitude dependenttime delay. If the voltage magnitude dependent time delay is applied, the timedelay will be longer if the voltage is higher, and the delay will be shorter if thevoltage is lower. If the frequency remains below the set value for a time periodcorresponding to the chosen time delay, the corresponding trip signal is issued. Toavoid an unwanted trip due to uncertain frequency measurement at low voltagemagnitude, a voltage controlled blocking of the function is available, that is, if thevoltage is lower than the set blocking voltage IntBlockLevel, the function isblocked and no START or TRIP signal is issued.10.1.6.1 Measurement principle M13354-6 v8The fundamental frequency of the measured input voltage is measuredcontinuously, and compared with the set value, StartFrequency. The frequencyfunction is dependent on the voltage magnitude. If the voltage magnitude decreasesbelow the setting IntBlockLevel, SAPTUF gets blocked, and the outputBLKDMAGN is issued. All voltage settings are made in percent of the settingUBase, which should be set as a phase-phase voltage in kV.To avoid oscillations of the output START signal, a hysteresis has been included.10.1.6.2 Time delay M13354-10 v9The time delay for underfrequency protection SAPTUF can be either a settabledefinite time delay or a voltage magnitude dependent time delay, where the timedelay depends on the voltage level; a high voltage level gives a longer time delayand a low voltage level causes a short time delay. For the definite time delay, thesetting tDelay sets the time delay.For the voltage dependent time delay the measured voltage level and the settingsUNom, UMin, Exponent, tMax and tMin set the time delay according to figure 127and equation . The setting TimerMode is used to decide what type of time delay toapply.Trip signal issuing requires that the underfrequency condition continues for at leastthe user set time delay tDelay. If the START condition, with respect to themeasured frequency ceases during this user set delay time, and is not fulfilled againwithin a user defined reset time, tReset, the START output is reset, after that thedefined reset time has elapsed. Here it should be noted that after leaving the1MRK 505 394-UEN A Section 10Frequency protectionLine differential protection RED650 2.2 IEC 269Technical manual
