with a long operation time and high sensitivity regarding the frequency difference.The phase angle difference setting can be set for steady state conditions.Another example is the operation of a power network that is disturbed by a faultevent: after the fault clearance a highspeed auto-reclosing takes place. This cancause a power swing in the net and the phase angle difference may begin tooscillate. Generally, the frequency difference is the time derivative of the phaseangle difference and will, typically oscillate between positive and negative values.When the circuit breaker needs to be closed by auto-reclosing after fault-clearancesome frequency difference should be tolerated, to a greater extent than in the steadycondition mentioned in the case above. But if a big phase angle difference isallowed at the same time, there is some risk that auto-reclosing will take placewhen the phase angle difference is big and increasing. In this case it should be saferto close when the phase angle difference is smaller.To fulfill the above requirements the synchrocheck function is provided withduplicate settings, one for steady (Manual) conditions and one for operation underdisturbed conditions (Auto).SynchroCheckUHighBusSC > 50 - 120 % of GblBaseSelBusUHighLineSC > 50 - 120 % of GblBaseSelLineUDiffSC < 0.02 – 0.50 p.u.PhaseDiffM < 5 - 90 degreesPhaseDiffA < 5 - 90 degreesFreqDiffM < 3 - 1000 mHzFreqDiffA < 3 - 1000 mHzFuse failFuse failLine voltage LinereferencevoltageBus voltageIEC10000079-2-en.vsdIEC10000079 V2 EN-USFigure 105: Principle for the synchrocheck function14.1.2.3 Energizing check M12310-3 v12The main purpose of the energizing check function is to facilitate the controlled re-connection of disconnected lines and buses to energized buses and lines.The energizing check function measures the bus and line voltages and comparesthem to both high and low threshold values. The output is given only when theactual measured conditions match the set conditions. Figure 106 shows twosubstations, where one (1) is energized and the other (2) is not energized. The lineSection 14 1MRK 511 401-UEN AControl286 Bay control REC670 2.2 IECApplication manual
