7SR210 & 7SR220 Description of OperationUnrestricted Page 30 of 94 ©2018 Siemens Protection Devices Limited3.2 Current Protection: Voltage Controlled Overcurrent (51V)– 7SR22Voltage controlled overcurrent is available in the 7SR22 relay.Each shaped overcurrent element 51-n Setting can be independently controlled by the level of measured(control) input voltage.For applied voltages above VCO Setting the 51-n element operates in accordance with its normal current setting(see 3.1.3). For input Ph-Ph control voltages below VCO Setting a multiplier (51-n Multiplier) is applied toreduce the 51-n pickup current setting.51-n Multiplier is applied to each phase independently when its control phase-phase voltage falls below VCOSetting. The voltage levels used for each phase over-current element are shown in the table below. Relays with aPh-N connection automatically calculate the correct Ph-Ph control voltage.Current Element Control VoltageIL1 V12IL2 V23IL3 V31The Voltage Controlled Overcurrent function (51V) can be inhibited from: -VCO VTSAction: Inhibit Operation of the VT Supervision function.VL151V Settingc&51V ElementEnabledDisabled<<<VL2VL351V VTS ActionOffInhibitSeeDelayedOvercurrent(51-n)VT Fail&51-n MultipliercV12V31V23cx IL1 51-n Settingcx IL2 51-n Settingcx IL3 51-n Setting L3L2L1Figure 3.2-1 Logic Diagram: Voltage Controlled Overcurrent Protection
