GE P24DM Technical Manual

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Directionality is achieved by using differet techniques depending on the application. The directional SEF can beused for:● Solidly earthed systems● Unearthed systems (insulated systems)● Compensated systems● Resistance earthed systemsThe device supports standard core-balanced directional control as well as Isin(f), Icos(f) and Wattmetriccharacteristics.If you are using directional SEF protection, you select the required polarisation using the SEF Options setting in theSEF PROTECTION column.8.4.1 WATTMETRIC CHARACTERISTICAnalysis has shown that a small angular difference exists between the spill current on healthy and faulted feedersfor earth faults on compensated networks. This angular difference gives rise to active components of currentwhich are in anti-phase to one another.E00617Active componentof residual current:Faulted FeederActive componentof residual current:Healthy FeederVres = -3VoOperateRestrainZero torque linefor 0 RCAKey:- Residual current on faulty feeder- Residual current on healthy feeder- Charging current from rest of system- Current through earthed coilIR1IR1IR3IR3IH1, IH2IH2IH1ILILFigure 58: Resistive components of spill currentConsequently, the active components of zero sequence power will also lie in similar planes, meaning an IEDcapable of detecting active power can make discriminatory decisions. If the Wattmetric component of zerosequence power is detected in the forward direction, then this would indicate fault on that feeder. If power isdetected in the reverse direction, then the fault must be present on an adjacent feeder or at the source.For operation of the directional earth fault element, all three of the settable thresholds must be exceeded; namelythe current ISEF>, the voltage ISEF>VNpol Set and the power PN> Setting.The power setting is called PN> and is calculated using residual quantities. The formula for operation is as follows:The PN> setting corresponds to:VresIrescos(f  fc) = 9VoIocos(f  fc)Chapter 6 - Current Protection Functions P24xM132 P24xM-TM-EN-2.1