Abstract:

The three-position mechanism represents a critical mechanical component in ultra-high voltage switch circuit breakers，with the copper nut serving as a pivotal element. Premature failure of this component can significantly compromise the operational stability and longevity of the circuit breaker. This comprehensive investigation employs advanced analytical techniques to elucidate the underlying fracture mechanisms of the copper nut. Utilizing a multifaceted analytical approach，the study systematically examined the fracture morphology and material characteristics. Optical microscopy，scanning electron microscopy，and metallographic microscopy were employed to scrutinize the fracture surface and microstructural features. Complementary analyses using X-ray fluorescence spectrometry and electronic universal testing machine characterized the material’s compositional and mechanical properties. The investigation revealed critical insights into the failure mechanism. Multiple crack initiation sites were identified within the fracture zone，characterized by coarse grain structures and an extensive network of precipitate particles localized at grain boundaries. The failure mode was definitively classified as cumulative fatigue damage. The primary crack source originated at the diameter transition of the shaft pin root’a structural stress concentration zone that represents the most vulnerable point in the copper nut’s mechanical design. The findings underscore the importance of structural geometry and material microstructure in predicting and mitigating mechanical failure in critical electromechanical components.

Key words: ultra-high voltage circuit breaker, three-position mechanism, copper nut, fatigue, fracture, stress concentration