8-36 L60 Line Phase Comparison System GE Multilin8.2 SINGLE-POLE TRIPPING 8 THEORY OF OPERATION88.2.2 PHASE SELECTIONThe L60 uses phase relations between current symmetrical components for phase selection. First, the algorithm validates ifthere is enough zero, positive, and negative-sequence currents for reliable analysis. The comparison is adaptive; that is,the magnitudes of the three symmetrical components used mutually as restraints confirm if a given component is largeenough to be used for phase selection. Once the current magnitudes are validated, the algorithm analyzes phase relationsbetween the negative and positive-sequence currents and negative and zero-sequence currents (when applicable) as illus-trated below.Figure 8–29: PHASE SELECTION PRINCIPLE (ABC PHASE ROTATION)Due to dual comparisons, the algorithm is very secure. For increased accuracy and to facilitate operation in weak systems,the pre-fault components are removed from the analyzed currents. The algorithm is very fast and ensures proper phaseselection before any of the correctly set protection elements operates.Under unusual circumstances such as weak-infeed conditions with the zero-sequence current dominating during anyground fault, or during cross-country faults, the current-based phase selector may not recognize any of the known fault pat-tern. If this is the case, voltages are used for phase selection. The voltage algorithm is the same as the current-based algo-rithm; for example, phase angles between the zero, negative, and positive-sequence voltages are used. The pre-faultvalues are subtracted prior to any calculations.The pre-fault quantities are captured and the calculations start when the disturbance detector (50DD) operates.When the trip command is issued by the trip output logic ( TRIP 1-POLE or TRIP 3-POLE ) and during open pole conditions( OPEN POLE OP ), the phase selector resets all its output operands and ignores any subsequent operations of the distur-bance detector.Figure 8–30: PHASE SELECTOR LOGIC837725A1.CDRAB,ABGCA,CAGBC,BCGAGAG,BCGI 2F I 2FI 1F I0FBGCG,ABGCG BG,CAG837027A4.CDRTRIP 1-POLESRCn 50DD OPTRIP 3-POLEOPEN POLE OPSRCn VT FUSE FAIL OPDISTANCE SOURCE:ANDFLEXLOGIC OPERANDSFLEXLOGIC OPERANDFLEXLOGIC OPERANDSETTINGDELAYDELAYI_1V_0V_1V_2I_0I_2FLEXLOGIC OPERANDSPHASE SELECT AGRESETSTARTPHASE SELECTORPHASE SELECT BGPHASE SELECT CGPHASE SELECT ABPHASE SELECT BCPHASE SELECT CAPHASE SELECT ABGPHASE SELECT BCGPHASE SELECT CAGPHASE SELECT 3PPHASE SELECT SLGPHASE SELECT MULTI-PPHASE SELECT VOID4 cycles500 ms00ORDELAY00.5 cycles
