9.1.3.5 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 study givesthe 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 voltages below 25%of rated voltageThis functionality can be achieved by using one CVGAPC function. The following shall be donein order to ensure proper operation of the function:1. Connect three-phase generator currents and voltages to one CVGAPC instance (forexample, GF05)2. SetCurrentInput to valueMaxPh3. SetVoltageInput to valueMinPh-Ph (it is assumed that minimum phase-to-phase voltageshall be used for restraining. Alternatively, positive sequence voltage can be used forrestraining by selectingPosSeq 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. SelectCurveType_OC1 to valueANSI Very inv8. If required set minimum operating time for this curve by using parametertMin_OC1(default value 0.05s)9. SetStartCurr_OC1 to value 185%10. SetVCntrlMode_OC1 toOn11. SetVDepMode_OC1 toSlope12. SetVDepFact_OC1 to value 0.2513. SetUHighLimit_OC1 to value 100%14. SetULowLimit_OC1 to value 25%Proper operation of the CVGAPC function made in this way can easily be verified by secondaryinjection. All other settings can be left at the default values. Furthermore the other built-inprotection elements can be used for other protection and alarming purposes.9.1.3.6 Loss of excitation protection for a generator M13088-182 v3Example will be given how by using positive sequence directional overcurrent protectionelement within a CVGAPC function, loss of excitation protection for a generator can beachieved. Let us assume that from rated generator data the following values are calculated:• Maximum generator capability to contentiously absorb reactive power at zero activeloading 38% of the generator MVA rating• Generator pull-out angle 84 degreesThis functionality can be achieved by using one CVGAPC function. The following shall be donein order to insure proper operation of the function:1. Connect three-phase generator currents and three-phase generator voltages to oneCVGAPC instance (for example, GF02)2. Set parameterCurrentInput toPosSeq3. Set parameterVoltageInput toPosSeq4. 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. Set parameterRCADir to value -84 degree (that is, current lead voltage for this angle)Section 9 1MRK 504 158-UEN AMultipurpose protection150Application manual
