4.4.1.5 ApplicationSince the negative sequence current quantities are not present during normal,balanced load conditions, the negative sequence overcurrent protection elementscan be set for faster and more sensitive operation than the normal phase-overcurrent protection for fault conditions occurring between two phases. Thenegative sequence overcurrent protection also provides a back-up protectionfunctionality for the feeder earth-fault protection in solid and low resistanceearthed networks.The negative sequence overcurrent protection provides the back-up earth-faultprotection on the high voltage side of a delta-wye connected power transformer forearth faults taking place on the wye-connected low voltage side. If an earth faultoccurs on the wye-connected side of the power transformer, negative sequencecurrent quantities appear on the delta-connected side of the power transformer.The most common application for the negative sequence overcurrent protection isprobably rotating machines, where negative sequence current quantities indicateunbalanced loading conditions (unsymmetrical voltages). Unbalanced loadingnormally causes extensive heating of the machine and can result in severe damageseven over a relatively short time period.Multiple time curves and time multiplier settings are also available for coordinatingwith other devices in the system.4.4.1.6 SignalsTable 358:NSPTOC Input signalsName Type Default DescriptionI2 SIGNAL 0 Negative phase sequence currentBLOCK BOOLEAN 0=False Block signal for activating the blocking modeENA_MULT BOOLEAN 0=False Enable signal for current multiplierTable 359:NSPTOC Output signalsName Type DescriptionOPERATE BOOLEAN OperateSTART BOOLEAN Start1YHT530004D05 D Section 4Protection functions615 series 449Technical Manual
