12.1.3.2 Negative sequence overcurrent protectionExample will be given how to use one CVGAPC function to provide negativesequence inverse time overcurrent protection for a generator with capability constantof 20s, and maximum continuous negative sequence rating of 7% of the generatorrated current.The capability curve for a generator negative sequence overcurrent protection, oftenused world-wide, is defined by the ANSI standard in accordance with the followingformula:2opNSrktII=æ öç ÷è øEQUATION1372 V1 EN (Equation 249)where:top is the operating time in seconds of the negative sequence overcurrent IEDk is the generator capability constant in secondsINS is the measured negative sequence currentIr is the generator rated currentBy defining parameter x equal to maximum continuous negative sequence rating ofthe generator in accordance with the following formula7% 0, 07x pu= =EQUATION1373 V1 EN (Equation 250)Equation 249 can be re-written in the following way without changing the value forthe operate time of the negative sequence inverse overcurrent IED:221opNSrk xtIx I×= æ öç ÷×è øEQUATION1374 V1 EN (Equation 251)In order to achieve such protection functionality with one CVGAPC functions thefollowing must be done:1MRK 502 071-UEN - Section 12Multipurpose protectionGenerator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 453Application manual
