CHAPTER 4: SETPOINTS PROTECTION869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–185VOLTAGE RESTRAINTRange: Disabled, EnabledDefault: DisabledThis setting enables or disables the Voltage Restraint function for the TOC element.When set to “Enabled” this feature lowers the Pickup value of each individual Phase TimeOvercurrent element in a fixed relationship with its corresponding phase input voltage.If cold load pickup, autoreclosing, or manual close blocking features are controlling theprotection, the Phase TOC Voltage Restraint does not work, even if “Enabled” is selected.Voltage restraint is used to lower the current pickup level for TOC function in linearproportion as shown in figure below. For example, if phase TOC PICKUP setting is set to1.000 XCT, in case of system faults cause generator terminal voltage drops to 0.4 pu(ratio of Phase-Phase Voltage/ VT Nominal Phase-phase voltage), the new pickup withvoltage restraint would be 1.000*0.4=0.400 xCT. During the fault condition when thevoltage drops, the overcurrent relay pickup also drops linearly and it should be verifiedthat for the limiting case the new voltage restraint relay pickup should be lower than(around 50% of) the fault current. Refer IEEE C37.102-2006, Annex-A for more details.Figure 4-65: Voltage Restraint characteristics for Phase TOCBLOCKRange: Off, Any FlexLogic operandDefault: OffOUTPUT RELAY XFor details see Common Setpoints.EVENTSRange: Enabled, DisabledDefault: EnabledTARGETSRange: Self-reset, Latched, DisabledDefault: Self-reset0.10.20.30.40.50.60.70.80.91.00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00892784A1.CDRMultiplier for Pickup CurrentPhase-Phase Voltage ÷ VT Nominal Phase-phase Voltage
