8.3.5 SettingsTable 147:SAPFRC Group settings (basic)Name Values (Range) Unit Step Default DescriptionOperation OffOn- - Off Operation Off / OnStartFreqGrad -10.00 - 10.00 Hz/s 0.01 0.50 Frequency gradient start value, the signdefines directiontTrip 0.000 - 60.000 s 0.001 0.200 Operate time delay in positive / negativefrequency gradient modeRestoreFreq 45.00 - 65.00 Hz 0.01 49.90 Restore is enabled if frequency is aboveset frequency valuetRestore 0.000 - 60.000 s 0.001 0.000 Restore time delay8.3.6 Operation principleRate-of-change frequency protection SAPFRC is used to detect fast power systemfrequency changes at an early stage. It has a settable definite time delay.To avoid anunwanted trip due to uncertain frequency measurement at low voltage magnitude, avoltage controlled blocking of the function is available from the preprocessingfunction that is, if the voltage is lower than the set blocking voltage in thepreprocessing function, the function is blocked and no START or TRIP signal isissued. If the frequency recovers, after a frequency decrease, a restore signal is issued.8.3.6.1 Measurement principleThe rate-of-change of the fundamental frequency of the selected voltage is measuredcontinuously, and compared with the set value(StartFreqGrad). If the voltagemagnitude decreases below the setting MinValFreqMeas in the preprocessingfunction, which is set as a percentage of a global base voltage parameter, SAPFRC isblocked and the output BLKDMAGN is issued. The sign of the settingStartFreqGrad, controls if SAPFRC reacts on a positive or on a negative change infrequency. If SAPFRC is used for decreasing frequency that is, the settingStartFreqGrad has been given a negative value, and a trip signal has been issued, a100 ms pulse is issued on the RESTORE output, when the frequency recovers to avalue higher than the setting RestoreFreq. A positive setting of StartFreqGrad, setsSAPFRC to START and TRIP for frequency increases.To avoid oscillations of the output START signal, a hysteresis has been included.8.3.6.2 Time delaySAPFRC has a settable definite time delay, tTrip.Trip signal issuing requires that SAPFRC condition continues for at least the user settime delay, tTrip. If the START condition, ceases during the delay time and is notSection 8 1MRK 511 287-UEN AFrequency protection188Technical manual
