1. select positive sequence current as measuring quantity for this CVGAPC function2. make sure that the base current value for CVGAPC function is equal to the generator ratedcurrent3. set k = 37.5 for the IEC standard or k = 41.4 for the ANSI standard4. setA_OC1= 1/1.162 = 0.74325. setC_OC1= 1/1.162 = 0.74326. setB_OC1 = 0.0 andP_OC1 = 2.07. setStartCurr_OC1 = 116%Proper timing of CVGAPC function made in this way can easily be verified by secondaryinjection. All other settings can be left at the default values. If required delayed time reset forOC1 step can be set in order to insure proper function operation in case of repetitive overloadconditions.Furthermore the other built-in protection elements can be used for other protection andalarming purposes.In the similar way rotor overload protection in accordance with ANSI standard can be achieved.8.1.3.4 Open phase protection for transformer, lines or generators and circuitbreaker head flashover protection for generators M13088-142 v3Example will be given how to use one CVGAPC function to provide open phase protection. Thiscan be achieved by using one CVGAPC function by comparing the unbalance current with a pre-set level. In order to make such a function more secure it is possible to restrain it by requiringthat at the same time the measured unbalance current must be bigger than 97% of themaximum phase current. By doing this it will be insured that function can only pickup if one ofthe phases is open circuited. Such an arrangement is easy to obtain in CVGAPC function byenabling the current restraint feature. The following shall be done in order to insure properoperation of the function:1. Connect three-phase currents from the protected object to one CVGAPC instance (forexample, GF03)2. SetCurrentInput to valueUnbalancePh3. SetEnRestrainCurr toOn4. SetRestrCurrInput toMaxPh5. SetRestrCurrCoeff to value 0.976. Set base current value to the rated current of the protected object in primary amperes7. Enable one overcurrent step (for example, OC1)8. Select parameterCurveType_OC1 to valueIEC Def. Time9. Set parameterStartCurr_OC1 to value 5%10. Set parametertDef_OC1 to desired time delay (for example, 2.0s)Proper operation of CVGAPC function made in this way can easily be verified by secondaryinjection. All other settings can be left at the default values. However it shall be noted that setvalues for restrain current and its coefficient will as well be applicable for OC2 step as soon asit is enabled.Furthermore the other built-in protection elements can be used for other protection andalarming purposes. For example, in case of generator application by enabling OC2 step withset pickup to 200% and time delay to 0.1s simple but effective protection against circuitbreaker head flashover protection is achieved.1MRK 505 355-UEN A Section 8Multipurpose protection139Application manual
