4 RATE OF CHANGE OF VOLTAGE PROTECTIONWhere there are very large loads, imbalances may occur, which could result in rapid decline in system voltage. Thesituation could be so bad that shedding one or two stages of load would be unlikely to stop this rapid voltagedecline. In such a situation, standard undervoltage protection will normally have to be supplemented withprotection that responds to the rate of change of voltage. An element is therefore required, which identifies thehigh rate of decline of voltage and adapts the load shedding scheme accordingly.Such protection can identify voltage variations occurring close to nominal voltage thereby providing early warningof a developing voltage problem. The element can also be used as an alarm to warn operators of unusually highsystem voltage variations.Rate of Change of Voltage protection is also known as dv/dt protection.4.1 RATE OF CHANGE OF VOLTAGE PROTECTION IMPLEMENTATIONThe dV/dt protection functions can be found in the the VOLT PROTECTION column under the sub-heading DV/DTPROTECTION. The dv/dt protection consists of two independent stages, which can be configured as either phase-to-phase or phase-to-neutral using the dv/dt Meas mode cell.4.2 RATE OF CHANGE OF VOLTAGE LOGICdv/dt1 Thresholddv /dt1 Trip A/ABdv/dt Meas ModeV00806dv/dt 1 StartA/ABdv/ dt1 BlockingFreq Not Founddv/dt1 Startdv/dt 1 TripV< Operate modeAny PhaseThree PhaseAveragingdv/dt1 AvgCycles-1dv/dt 1 FunctionNegativePositiveBothDisableddV/ dtReset& 1&1&&&1&&11DT&×dv/dt1 Thresholddv/ dt1 Trip B/BCdv/dt Meas Modedv/dt1 StartB/BCFreq Not FoundAveragingdv/dt1 AvgCycles-1dV/ dtReset& 1 DT&×dv/dt1 TimeDelaydv/dt1 TimeDelaydv/dt1 Thresholddv/dt 1 Trip C/CAdv/dt Meas Modedv/dt1 StartC/CAFreq Not FoundAveragingdv/dt1 AvgCycles-1dV/ dtReset& 1 DT&×dv/dt1 TimeDelay111VAVABVBVBCVCVCAFigure 112: Rate of Change of Voltage protection logicChapter 10 - Voltage Protection Functions P14x216 P14xEd1-TM-EN-1
