CHAPTER 4: SETPOINTS PROTECTION889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–225AuxiliaryUndervoltage (27X)The 889 relay provides two identical Auxiliary Undervoltage (UV) elements per protectiongroup, or a total of 12 elements. Each Auxiliary Undervoltage element may be used toprotect voltage sensitive loads and system components against sustained undervoltageconditions. This element may be used for permissive functions, initiation of the sourcetransfer schemes and similar functions.The Auxiliary Undervoltage element may be set as an instantaneous element with no timedelay or as a time delayed element which can be programmed with definite time, inversetime or FlexCurves. The Auxiliary Undervoltage element has a programmable minimumoperating threshold to prevent undesired operation when voltage is not available. Theinput voltage is the auxiliary voltage.The settings of this function are applied to auxiliary voltage input to produce Pickup andTrip flags. The Auxiliary UV Pickup flag is asserted when the auxiliary input voltage is belowthe PKP value. The Auxiliary UV Trip flag is asserted if the element stays picked up for thetime defined by Pickup time delay or for the time defined by the selected inverse curve/FlexCurve. The element drops from Pickup without operation if the measured voltage risesabove 102 to 103% of the Pickup value before the time for operation is reached.The minimum voltage setting selects the operating voltage below which the element isblocked (a setting of “0” will allow a dead source to be considered a fault condition).This element may be used to give a desired time-delay operating characteristic versus theapplied voltage, or as a definite time element. For the inverse time setpoint, theundervoltage delay setpoint defines a family of curves as described in UndervoltageCurves.Path: Setpoints > Protection > Group 1(6) > Voltage Elements > Auxiliary UV 1(X)FUNCTIONRange: Disabled, Trip, Alarm, Latched Alarm, ConfigurableDefault: DisabledPICKUPRange: 0.00 to 1.50 x VT in steps of 0.01 x VTDefault: 1.00 x VTThis setting sets the Auxiliary Undervoltage Pickup level specified per times VT. Forexample, a Pickup setting of 0.80 x VT with a 13800:115 VT translates into 11.04kV (or92V secondary).MINIMUM VOLTAGERange: 0.00 to 1.50 x VT in steps of 0.01 x VTDefault: 0.20 x VTThis setting sets the minimum operating voltage for the undervoltage Pickup levelspecified per times VT.UNDERVOLTAGE CURVESRange: Definite Time, Inverse Time, FlexCurves A/B/C/DDefault: Definite TimeThis setting provides the selection of definite time delay or time delay inverseundervoltage curves. In the case of FlexCurves, the voltage ratio is reversed. For moreinformation refer to the equation and note regarding FlexCurves in Undervoltage Curves.PICKUP DELAYRange: 0.000 to 6000.000 s in steps of 0.001 sDefault: 1.000 sIf Inverse Time is selected as an Undervoltage Curve setpoint, the Pickup Delay value isloaded to variable D in the curve formula. For more information, refer to UndervoltageCurves.
