5-66 L60 Line Phase Comparison System GE Multilin5.3 SYSTEM SETUP 5 SETTINGS55.3.2 POWER SYSTEMPATH: SETTINGS ÖØ SYSTEM SETUP ÖØ 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 may 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 a safeperiod 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. Note that this setting informs the relay of theactual system phase sequence, either ABC or ACB. CT and VT inputs on the relay, labeled as A, B, and C, must be con-nected 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 that are configured for the signal source:phase voltages takes precedence, followed by auxiliary voltage, then phase currents, and finally ground current.For three phase selection, phase A is used for angle referencing ( ), while Clarke transformation of thephase signals is used for frequency metering and tracking ( ) for better performance dur-ing 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 will always display zero degrees and all other phase angles will be relative to this sig-nal. If the pre-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. These results in very precise correlation of time tagging in the event recorder betweendifferent UR-series relays provided the relays have an IRIG-B connection.FREQUENCY TRACKING should only be set to "Disabled" in very unusual circumstances; consult the factory for spe-cial variable-frequency applications.The frequency tracking feature will function only when the L60 is in the “Programmed” mode. If the L60 is “Not Pro-grammed”, then metering values will be available but may exhibit significant errors.When voltage is supplied to the relay through a VT, it is advisable to assign a source configured with aphase VT voltage (source 3 or 4) to track system frequency from voltage. Source 1 should be assigned totrack frequency from current. POWER SYSTEMNOMINAL FREQUENCY:60 HzRange: 25 to 60 Hz in steps of 1MESSAGE PHASE ROTATION:ABCRange: ABC, ACBMESSAGE FREQUENCY AND PHASEREFERENCE: SRC 1Range: SRC 1, SRC 2MESSAGE FREQUENCY TRACKING:EnabledRange: Disabled, EnabledVANGLE REF V A=VFREQUENCY 2V A V B– V C–( ) 3⁄=NOTENOTENOTE
