GE Multilin F60 Feeder Protection System 8-58 THEORY OF OPERATION 8.2 FAULT LOCATOR88.2FAULT LOCATOR 8.2.1 FAULT TYPE DETERMINATIONFault type determination is required for calculation of fault location – the algorithm uses the angle between the negative andpositive sequence components of the relay currents. To improve accuracy and speed of operation, the fault components ofthe currents are used; that is, the pre-fault phasors are subtracted from the measured current phasors. In addition to theangle relationships, certain extra checks are performed on magnitudes of the negative and zero-sequence currents.The single-ended fault location method assumes that the fault components of the currents supplied from the local (A) andremote (B) systems are in phase. The figure below shows an equivalent system for fault location.Figure 8–1: EQUIVALENT SYSTEM FOR FAULT LOCATIONThe following equations hold true for this equivalent system.(EQ 8.1)where: m = sought pu distance to fault, Z = positive sequence impedance of the line.The currents from the local and remote systems can be parted between their fault (F) and pre-fault load (pre) components:(EQ 8.2)and neglecting shunt parameters of the line:(EQ 8.3)Inserting the IA and IB equations into the VA equation and solving for the fault resistance yields:(EQ 8.4)Assuming the fault components of the currents, IAF and I BF are in phase, and observing that the fault resistance, as imped-ance, does not have any imaginary part gives:(EQ 8.5)where: Im() represents the imaginary part of a complex number. Solving the above equation for the unknown m creates thefollowing fault location algorithm:(EQ 8.6)where * denotes the complex conjugate and .Depending on the fault type, appropriate voltage and current signals are selected from the phase quantities before applyingthe two equations above (the superscripts denote phases, the subscripts denote stations).For AG faults:(EQ 8.7)mZ (1-m)ZR FZ A Z BE A E BV A V BV FI A I BLocal busRemotebusdistance to fault842780A1.CDRV A m Z I A R F I A I B+ +=I A I AF I Apre+=I B I BF I Apre–=R FV A m Z I A –I AF 1 I BFI AF--------+ -----------------------------------=Im V A m Z I A –I AF----------------------------------- 0=m Im V A I AF Im Z I A I AF ----------------------------------------=I AF I A I Apre–=V A V AA= , I A I AA K0 I0A+=
