GE P24DM Technical Manual

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6.2 FREQUENCY-SUPERVISED R.O.C.O.F LOGICStage 1V00853Stg1 df /dt+t Trp&Enabled&1V df/dtf+df /dt 1 df/dt X-1df /dt Avg.CyclesFrequencydeterminationf +df/ dt 1 freqFreq Avg.CyclesV FrequencyaveragingX-1FrequencydeterminationAdv Freq InhFreq Not FoundVEnabledUV Block1Stg1 Block1Freq HighFreq Low1f+df/dt 1 StatusBothPositiveNegative11DisabledNote: This diagram does not show all stages . Other stages follow similar principles.Figure 116: Frequency-supervised rate of change of frequency logic (single stage)6.3 APPLICATION NOTES6.3.1 FREQUENCY-SUPERVISED R.O.C.O.F EXAMPLEIn the load shedding scheme below, we assume that for falling frequency conditions, the system can be stabilisedat frequency f2 by shedding a stage of load. For slow rates of decay, this can be achieved using theunderfrequency protection element set at frequency f1 with a suitable time delay. However, if the generationdeficit is substantial, the frequency will rapidly decrease and it is possible that the time delay imposed by theunderfrequency protection will not allow for frequency stabilisation. In this case, the chance of system recoverywill be enhanced by disconnecting the load stage based on a measurement of rate of change of frequency andbypassing the time delay.Chapter 11 - Frequency Protection Functions P24xM232 P24xM-TM-EN-2.1