11.1.3.5 Voltage restrained overcurrent protection for generator and step-uptransformer M13088-158 v4Example will be given how to use one CVGAPC function to provide voltage restrainedovercurrent protection for a generator. Let us assume that the time coordination studygives the following required settings:• Inverse Time Over Current TOC/IDMT curve: ANSI very inverse• Pickup current of 185% of generator rated current at rated generator voltage• Pickup current 25% of the original pickup current value for generator voltagesbelow 25% of rated voltageThis functionality can be achieved by using one CVGAPC function. The followingshall be done in order to ensure proper operation of the function:1. Connect three-phase generator currents and voltages to one CVGAPC instance(for example, GF05)2. Set CurrentInput to value MaxPh3. Set VoltageInput to value MinPh-Ph (it is assumed that minimum phase-to-phasevoltage shall be used for restraining. Alternatively, positive sequence voltage canbe used for restraining by selecting PosSeq for this setting parameter)4. Set base current value to the rated generator current primary amperes5. Set base voltage value to the rated generator phase-to-phase voltage in kV6. Enable one overcurrent step (for example, OC1)7. Select CurveType_OC1 to value ANSI Very inv8. If required set minimum operating time for this curve by using parametertMin_OC1 (default value 0.05s)9. Set PickupCurr_OC1 to value 185%10. Set VCntrlMode_OC1 to On11. Set VDepMode_OC1 to Slope12. Set VDepFact_OC1 to value 0.2513. Set VHighLimit_OC1 to value 100%14. Set VLowLimit_OC1 to value 25%Proper operation of the CVGAPC function made in this way can easily be verified bysecondary injection. All other settings can be left at the default values. Furthermore theother built-in protection elements can be used for other protection and alarmingpurposes.11.1.3.6 Loss of excitation protection for a generator M13088-182 v3Example will be given how by using positive sequence directional overcurrentprotection element within a CVGAPC function, loss of excitation protection for a1MRK 511 401-UUS A Section 11Multipurpose protectionBay control REC670 2.2 ANSI 283Application manual
