When the equation 99 is compared with the equation 101 for the inverse time characteristic ofthe OC1 it is obvious that if the following rules are followed:1. set k equal to the generator negative sequence capability value2. setA_OC1 equal to the value 1/x23. setB_OC1 = 0.0,C_OC1=0.0 andP_OC1=2.04. setStartCurr_OC1 equal to the value xthen the OC1 step of the CVGAPC function can be used for generator negative sequenceinverse overcurrent protection.For this particular example the following settings shall be entered to insure proper functionoperation:1. select negative sequence current as measuring quantity for this CVGAPC function2. make sure that the base current value for the CVGAPC function is equal to the generatorrated current3. setk_OC1 = 204. setA_OC1= 1/0.072 = 204.08165. setB_OC1 = 0.0, C_OC1 = 0.0 andP_OC1 = 2.06. setStartCurr_OC1 = 7%Proper timing of the 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 ensure proper function operation in case of repetitiveunbalance conditions.Furthermore the other built-in protection elements can be used for other protection andalarming purposes (for example, use OC2 for negative sequence overcurrent alarm and OV1 fornegative sequence overvoltage alarm).10.1.3.3 Generator stator overload protection in accordance with IEC or ANSIstandards M13088-81 v3Example will be given how to use one CVGAPC function to provide generator stator overloadprotection in accordance with IEC or ANSI standard if minimum-operating current shall be setto 116% of generator rating.The generator stator overload protection is defined by IEC or ANSI standard for turbogenerators in accordance with the following formula:21opmrktII=æ ö -ç ÷è øEQUATION1376 V1 EN-US (Equation 103)where:top is the operating time of the generator stator overload IEDk is the generator capability constant in accordance with the relevant standard (k = 37.5 for the IECstandard or k = 41.4 for the ANSI standard)Im is the magnitude of the measured currentIr is the generator rated current1MRK 511 358-UEN A Section 10Multipurpose protection207Application manual
