5-144 L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUALSYSTEM SETUP CHAPTER 5: SETTINGS55.4.2 Power systemSETTINGS SYSTEM SETUP POWER SYSTEMThe power system NOMINAL FREQUENCY value is used as a default to set the digital sampling rate if the system frequencycannot be measured from available signals. This can happen if the signals are not present or are heavily distorted. Beforereverting to the nominal frequency, the frequency tracking algorithm holds the last valid frequency measurement for asafe period of time while waiting for the signals to reappear or for the distortions to decay.The phase sequence of the power system is required to properly calculate sequence components and power parameters.The PHASE ROTATION setting matches the power system phase sequence and informs the relay of the actual system phasesequence, either ABC or ACB. CT and VT inputs on the relay, labelled as A, B, and C, must be connected to system phases A,B, and C for correct operation.The FREQUENCY AND PHASE REFERENCE setting determines which signal source is used (and hence which AC signal) forphase angle reference. The AC signal used is prioritized based on the AC inputs configured for the signal source. Phasevoltages takes precedence, followed by auxiliary voltage, then phase currents, and finally ground current.For three phase selection, phase A is used for angle referencing (VANGLE REF = VA), while Clarke transformation of the phasesignals is used for frequency metering and tracking (VFREQUENCY = (2VA - V B - VC) / 3) for better performance during fault,open pole, and VT and CT fail conditions.The phase reference and frequency tracking AC signals are selected based upon the source configuration, regardless ofwhether or not a particular signal is actually applied to the relay.Phase angle of the reference signal always displays zero degrees and all other phase angles are relative to this signal. If thepre-selected reference signal is not measurable at a given time, the phase angles are not referenced.The phase angle referencing is done via a phase locked loop, which can synchronize independent UR-series relays if theyhave the same AC signal reference. This results in very precise correlation of phase angle indications between different UR-series relays.FREQUENCY TRACKING is set to “Disabled” only in unusual circumstances; consult GE Grid Solutions for special variable-frequency applications.The nominal PHASE VT F5 SECONDARY voltage setting is the voltage across the relay input terminals when nominalvoltage is applied to the VT primary.For example, on a system with a 13.8 kV nominal primary voltage and with a 14400:120 volt VT in a deltaconnection, the secondary voltage is 115; that is, (13800 / 14400) × 120. For a wye connection, the voltage valueentered must be the phase to neutral voltage, which is 115 / = 66.4.On a 14.4 kV system with a delta connection and a VT primary to secondary turns ratio of 14400:120, the voltagevalue entered is 120; that is, 14400 / 120. POWER SYSTEM NOMINAL FREQUENCY:60 HzRange: 25 to 60 Hz in steps of 1 PHASE ROTATION:ABCRange: ABC, ACB FREQUENCY AND PHASEREFERENCE: SRC 1Range: SRC 1, SRC 2, SRC 3, SRC 4 FREQUENCYTRACKING:EnabledRange: Disabled, EnabledThe frequency tracking feature functions only when the L60 is in the “Programmed” mode. If the L60 is “NotProgrammed,” then metering values are available but can exhibit significant errors.
