Retrospective Vibration Vector Analysis of Periodic Synchronous Vibration in Nuclear Steam Turbine Generator Units

This retrospective study reanalyzes 59 archived synchronous (1X) amplitude–phase observations from two half-speed nuclear steam turbine generator units: 25 Type-A 6H and 34 Type-B 8H points. A constant complex response and a rotating slow component are fitted jointly to the reconstructed real and imaginary parts using Powell optimization. The baseline magnitudes are 27.96 and 82.04 μm, the slow-component magnitudes are 8.11 and 6.21 μm, and the periods are 340.27 and 365.02 min, respectively. Full-record amplitude R2 values are 0.918 and 0.883. With the last approximately 30% of each record withheld, the amplitude RMSE values are 4.19 and 2.85 μm and the R2 values are −0.782 and 0.185, with modest improvement over a simple periodic amplitude fit. Residual structure and time-window sensitivity limit prediction. Archived seal inspections and cooling trends provide context for competing physical explanations. Neither the decomposition nor the conditional film-thickness illustration identifies a unique heat source or validates a seal-to-bow causal chain. The results support description and comparison of the retained response patterns.