Flexible optical current transformers(CTs) have found extensive applications in the hydropower field

laying the foundation for quantitative transformation of main protection for generators with odd branches. In the case of the right bank generator at Xiangjiaba power station

comprising 7 branches per phase

a comprehensive internal fault analysis and quantitative design process for main protection were conducted. It is recommended to adopt the "3-1-3" branch grouping method. While the main protection dead zone is small (0.5%)

there exists a protection dead zone for phase-to-phase short circuits—occurring between the 4th branches where CTs are not installed in each phase. Leveraging the flexibility of flexible optical current transformers

this dead zone can be eliminated by adding optical CTs for the 4th branches in each phase and corresponding incomplete longitudinal differential protection. This quantitative transformation approach for main protection will serve as a reference for the subsequent technical transformation of large generators with odd branches