Equipment protection, such as for motors and generatorsThe setting has to be well above the highest occurring "normal" frequency and well belowthe highest acceptable frequency for the equipment.Power system protection, by generator sheddingThe setting must be above the highest occurring "normal" frequency and below the highestacceptable frequency for power stations, or sensitive loads. The setting level, the numberof levels and the distance between two levels (in time and/or in frequency) depend verymuch on the characteristics of the power system under consideration. The size of the"largest loss of load" compared to "the size of the power system" is a critical parameter.In large systems, the generator shedding can be set at a fairly low frequency level, and thetime delay is normally not critical. In smaller systems the frequency PICKUP level has tobe set at a higher value, and the time delay must be rather short.8.3 Rate-of-change frequency protection SAPFRC (81)8.3.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberRate-of-change frequency protection SAPFRCdf/dt ><SYMBOL-N V1 EN818.3.2 ApplicationRate-of-change frequency protection (SAPFRC, 81), is applicable in all situations, wherereliable detection of change of the fundamental power system voltage frequency isneeded. SAPFRC (81) can be used both for increasing frequency and for decreasingfrequency. SAPFRC (81) provides an output signal, suitable for load shedding orgenerator shedding, generator boosting, HVDC-set-point change, gas turbine start up andso on. Very often SAPFRC (81) is used in combination with a low frequency signal,especially in smaller power systems, where loss of a fairly large generator will requirequick remedial actions to secure the power system integrity. In such situations loadshedding actions are required at a rather high frequency level, but in combination with alarge negative rate-of-change of frequency the underfrequency protection can be used ata rather high setting.Section 8 1MRK 511 286-UUS AFrequency protection168Application manual
