Stage Element Frequency Setting (Hz) Time Setting (Sec.)2 Stage 6(f+t) 51.0 20The relatively long time delays are intended to provide time for the system controls to respond and will work well ina situation where the increase of system frequency is slow.For situations where rapid increase of frequency is expected, the protection scheme above could be supplementedby rate of change of frequency protection elements.In the system shown below, the generation in the MV bus is sized according to the loads on that bus, whereas thegenerators linked to the HV bus produce energy for export to utility. If the links to the grid are lost, the generationwill cause the system frequency to rise. This rate of rise could be used to isolate the MV bus from the HV system.E00857LoadLoadTo utilityLocal generationIPP generationHV busMV busFigure 121: Power system segregation based upon frequency measurementsChapter 11 - Frequency Protection Functions P14D222 P14D-TM-EN-8
