Generator I22t Requirements for System Faults

The design of turbine generators is strongly influenced by their requirements for negative sequence duty. In conjunction With a current revision to the ANSI C-50 standards, a review was made of the system requirements for I22t capability in generators of directly cooled sizes, tied into high voltage transmission systems. The results of these studies, which is the subjict of this paper, indicate that maximum expected I22t duty for system faults is less than two, or roughly one-third of the lowest I22t values specified in the revised standard, indicating also that a comfortable margin will still exist between system requirements and machine capabilities.