set to “Delta”) and residual voltage (Uo). Both alternatives are covered by setting theconfiguration parameter Phase voltage Meas to "Accurate".When the Phase voltage Meas setting is set to "Ph-to-ph without Uo" and only phase-to-phase voltages are available (but not Uo), only short-circuit measuring loops (faultloops “AB Fault”, “BC Fault” or “CA Fault” or “ABC Fault”) can be measuredaccurately. In this case, the earth-fault loops (fault loops either “AG Fault”, “BGFault” or “CG Fault”) cannot provide correct fault distance estimates and thetriggering of the function in case of earth fault is automatically disabled.5.4.5 ApplicationThe main objective of the feeder terminals is a fast, selective and reliable operation infaults inside the protected feeder. In addition, information on the distance to the faultpoint is very important for those involved in operation and maintenance. Reliableinformation on the fault location greatly decreases the downtime of the protectedfeeders and increases the total availability of a power system.SCEFRFLO provides impedance-based fault location. It is designed for radiallyoperated distribution systems and is applicable for locating short circuits in all kindsof distribution networks. Earth faults can be located in effectively earthed and lowresistance/low-reactance earthed networks. Under certain limitations, SCEFRFLOcan also be applied for earth-fault location in unearthed distribution networks.Configuration exampleA typical configuration example for SCEFRFLO triggering is illustrated in Figure 257where external triggering is applied, that is, Calculation Trg mode is set to “External”.The OPERATE signal from non-directional overcurrent function PHLPTOC is used toprovide an indication of a short circuit fault. The OPERATE signal from the directionalearth-fault function DEFLPDEF is used to provide an indication of an earth fault at theprotected feeder.SCEFRFLO with the autoreclosing functionWhen SCEFRFLO is used with the autoreclosing sequence, the distance estimatefrom the first trip is typically the most accurate one. The fault distance estimates fromsuccessive trips are possible but accuracy can be decreased due to inaccurate loadcompensation. During the dead time of an autoreclosing sequence, the load conditionof the feeder is uncertain.The triggering of SCEFRFLO can also be inhibited during the autoreclosingsequence. This is achieved by connecting the inverted READY signal from theautoreclosing function DARREC, which indicates that the autoreclosing sequence isin progress, to the BLOCK input of SCEFRFLO. Blocking of the SCEFRFLOtriggering is suggested during the autoreclosing sequence when the loadcompensation or steady-state asymmetry elimination is based on the delta quantities.This applies to the short circuit faults when Load Com PP loops is set to “Enabled” or,for earth faults, when EF algorithm Sel is set to “Load compensation” or “Loadmodelling”.Section 5 1MRS758755 AProtection related functions502 REC615 and RER615Technical Manual
