10.2.2 FunctionalityOverfrequency protection function SAPTOF is applicable in all situations, wherereliable detection of high fundamental power system frequency is needed.Overfrequency occurs because of sudden load drops or shunt faults in the powernetwork. Close to the generating plant, generator governor problems can also causeover frequency.SAPTOF measures frequency with high accuracy, and is used mainly for generationshedding and remedial action schemes. It is also used as a frequency stage initiatingload restoring. A definite time delay is provided for operate.SAPTOF is provided with an undervoltage blocking.The operation is based on positive sequence voltage measurement and requires twophase-phase or three phase-neutral voltages to be connected. For information abouthow to connect analog inputs, refer to Application manual/IED application/Analoginputs/Setting guidelines10.2.3 Function blockIEC06000280_2_en.vsdSAPTOFU3P*BLOCKBLKTRIPTRIPSTARTBLKDMAGNFREQIEC06000280 V2 ENFigure 265: SAPTOF function block10.2.4 SignalsTable 309:SAPTOF Input signalsName Type Default DescriptionU3P GROUPSIGNAL- Three phase group signal for voltage inputsBLOCK BOOLEAN 0 Block of functionBLKTRIP BOOLEAN 0 Blocking operate outputTable 310:SAPTOF Output signalsName Type DescriptionTRIP BOOLEAN General trip signalSTART BOOLEAN General start signalBLKDMAGN BOOLEAN Measurement blocked due to low amplitudeFREQ REAL Measured frequency1MRK502052-UEN B Section 10Frequency protection549Technical manual
