9.3.4 SignalsTable 166:SAPFRC Input signalsName Type Default DescriptionU3P GROUPSIGNAL- Three phase group signal for voltage inputsBLOCK BOOLEAN 0 Block of functionTable 167:SAPFRC Output signalsName Type DescriptionTRIP BOOLEAN Operate/trip signal for frequency gradientSTART BOOLEAN Start/pick-up signal for frequency gradientRESTORE BOOLEAN Restore signal for load restoring purposesBLKDMAGN BOOLEAN Blocking indication due to low amplitude9.3.5 SettingsTable 168: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 delay9.3.6 Operation principleRate-of-change frequency protection SAPFRC is used to detect fast power systemfrequency changes, increase as well as, decrease at an early stage. SAPFRC has asettable definite time delay. If the rate-of-change of frequency remains below theset value, for negative rate-of-change, for a time period equal to the chosen timedelay, the TRIP signal is issued. If the rate-of-change of frequency remains abovethe set value, for positive rate-of-change, for a time period equal to the chosen timedelay, the TRIP signal is issued. To avoid an unwanted trip due to uncertainfrequency measurement at low voltage magnitude, a voltage controlled blocking ofthe function is available from the preprocessing function that is, if the voltage islower than the set blocking voltage in the preprocessing function, the function isblocked and no START or TRIP signal is issued. If the frequency recovers, after afrequency decrease, a restore signal is issued.1MRK 502 034-UEN - Section 9Frequency protection263Technical Manual
