Calculations of generator source short- circuit current according to ANSI/IEEE and IEC standards, with EMTP verifications

For the interruption of a large generator source-short-circuit current, a current zero may not be obtained at the contact parting time of the circuit breaker. Large generators which have high X/R ratio, and depending upon the relative impedances and time constants the dc component can be higher than the ac decaying component delaying the occurrence of current zero well beyond contact parting time of the circuit breaker. The subject is well addressed in the current literature, though not the calculations of it. This paper presents calculations of a large practical generator using ANSI/IEEE and IEC standards with verifications of results using EMTP. It demonstrates large differences which impact the selection of generator circuit breaker interrupting duties.