will, with a delay for example 10 s, detect the situation when the generator is not connected tothe grid (standstill) and activate the overcurrent function. The overvoltage function will detectthe situation when the generator is taken into operation and will disable the overcurrentfunction. The overcurrent function will have a pick-up value about 50% of the rated current ofthe generator. The trip delay will be about 50 ms.8.1.3 Setting guidelines IP15009-1 v2GUID-F7AA2194-4D1C-4475-8853-C7D064912614 v4When inverse time overcurrent characteristic is selected, the operate time ofthe stage will be the sum of the inverse time delay and the set definite timedelay. Thus, if only the inverse time delay is required, it is important to set thedefinite time delay for that stage to zero.M13088-237 v4The parameters for the general current and voltage protection function (CVGAPC) are set viathe local HMI or Protection and Control Manager (PCM600).GlobalBaseSel: Selects the global base value group used by the function to define (IBase),(UBase) and (SBase).The overcurrent steps has aIMinx (x=1 or 2 depending on step) setting to setthe minimum operate current. SetIMinx belowStartCurr_OCx for every step toachieve ANSI reset characteristic according to standard. IfIMinx is set aboveStartCurr_OCx for any step the ANSI reset works as if current is zero whencurrent drops belowIMinx.8.1.3.1 Directional negative sequence overcurrent protection M13088-3 v5Directional negative sequence overcurrent protection is typically used as sensitive earth-faultprotection of power lines where incorrect zero sequence polarization may result from mutualinduction between two or more parallel lines. Additionally, it can be used in applications onunderground cables where zero-sequence impedance depends on the fault current returnpaths, but the cable negative-sequence impedance is practically constant. It shall be notedthat directional negative sequence OC element offers protection against all unbalance faults(phase-to-phase faults as well). Care shall be taken that the minimum pickup of suchprotection function shall be set above natural system unbalance level.An example will be given, how sensitive-earth-fault protection for power lines can be achievedby using negative-sequence directional overcurrent protection elements within a CVGAPCfunction.This functionality can be achieved by using one CVGAPC function. The following shall be doneto ensure proper operation of the function:1. Connect three-phase power line currents and three-phase power line voltages to oneCVGAPC instance (for example, GF04)2. SetCurrentInput toNegSeq (please note that CVGAPC function measures I2 current andNOT 3I2 current; this is essential for proper OC pickup level setting)3. SetVoltageInput to-NegSeq (please note that the negative sequence voltage phasor isintentionally inverted in order to simplify directionality4. Set base currentIBase value equal to the rated primary current of power line CTs5. Set base voltageUBase value equal to the rated power line phase-to-phase voltage in kV6. SetRCADir to value +65 degrees (NegSeq current typically lags the invertedNegSeqvoltage for this angle during the fault)7. SetROADir to value 90 degree8. SetLowVolt_VM to value 2% (NegSeq voltage level above which the directional elementwill be enabled)Section 8 1MRK 505 355-UEN AMultipurpose protection134Application manual
