Since the identification of open-phase fault vulnerability at nuclear plants worldwide, the nuclear industry has recognized that no relevant automatic detection/protection scheme existed for this new failure mode. TVA's Power System Analysis team has developed a multifaceted solution that has led to dramatic cost savings compared to other industry approaches. Significant advancements were made on several fronts. These include enhancements to analytical modeling of key power system components; the development of new academically-sound power system analysis methodologies; incorporation of those methodologies into industry standard validated analysis software; and verification of key elements in a first-of-a-kind field test. These efforts have enabled TVA to develop an innovative and comprehensive solution: apply proven protective relaying at the Class 1E power system boundary along with open-phase detection technology for standby transformers. This solution, which is transferable to other nuclear plants, provides direct assessment of the key parameter needed to ensure safety-related equipment protection and increases nuclear safety by allowing the safety-related power system to remain connected to preferred offsite power whenever possible. The timely development of this innovative and cost-saving approach has allowed virtually seamless alignment with existing industry standards, NRC expectations, and the NEI industry initiative on open-phase. It is projected to save TVA greater than $17M when compared to other industry solutions. Individual elements of this effort have been nationally and internationally recognized as key contributors by various entities, including NEI, NRC, INPO, WANO, and EPRI. [ABSTRACT FROM AUTHOR]
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