8.16.2.3 Undervoltage seal-in GUID-13BE02D3-1322-4075-859B-617CFF608657 v7In the case of a generator with a static excitation system, which receives its power fromthe generator terminals, the magnitude of a sustained phase short-circuit currentdepends on the generator terminal voltage. In case of a nearby multi-phase fault, thegenerator terminal voltage may drop to quite low level, for example, less than 25%,and the generator fault current may consequently fall below the pickup level of theovercurrent protection. The short-circuit current may drop below the generator ratedcurrent after 0.5...1 s. Also, for generators with an excitation system not fed from thegenerator terminals, a fault can occur when the automatic voltage regulator is out ofservice. In such cases, to ensure tripping under such conditions, overcurrent protectionwith undervoltage seal-in can be used.To apply the VRPVOC(51V) function, the configuration is done according to figure94. As seen in the figure, the pickup of the overcurrent stage will enable theundervoltage stage. Once enabled, the undervoltage stage will start a timer, whichcauses function tripping, if the voltage does not recover above the set value. To ensurea proper reset, the function is blocked two seconds after the trip signal is issued.Trip outputOROR tANSI12000183-1-en.vsdVRPVOC (51V)I3P*I3P*V3P*V3P*BLOCKBLOCKBLKOCBLKOCBLKUVBLKUVTRIPTRIPTROCTROC27 Trip27 TripPICKUPPICKUPPU_OCPU_OC27 PU27 PUANSI12000183 V1 EN-USFigure 94: Undervoltage seal-in of current pickup8.16.3 Setting guidelines GUID-2AE85EC4-669E-47C0-ADD4-3DBA83581096 v28.16.3.1 Explanation of the setting parameters GUID-9B777E6D-602B-4214-9170-A44ED2D725BF v3Operation: Set to On in order to activate the function; set to Off to switch off thecomplete function.1MRK 511 401-UUS A Section 8Current protectionBay control REC670 2.2 ANSI 237Application manual
