The ultra-high-voltage direct-current (UHVDC) bushings (i.e.

the valve-side bushing of the converter transformer and the DC wall bushing) are critical components connecting the converter transformer to the valve hall and the DC yard. They serve both as insulation between the lead and ground and as mechanical support. Due to the extremely complex operating conditions

DC bushings are subjected to prolonged electrical

thermal

and mechanical overstress. The coupling of electrical

thermal

and mechanical fields within the bushing can easily lead to the degradation or even premature failure of the internal electrical contact system and solid insulation. Such issues pose significant challenges to the safe and reliable operation of converter transformers and valve halls. This paper reviews recent research progress in the electro-thermal characteristics

temperature field analysis

structural optimization

and electrical contact failure mechanisms of UHVDC bushings. First

the structural features and key technologies of widely used bushing types are introduced. The characteristics of electro-thermal stresses under complex operating conditions are identified

and typical failure modes and coupled electro-thermal-mechanical behaviors are analyzed. Then

a comprehensive review is conducted

covering electro-thermal characteristics

insulation structure optimization

and failure mechanisms of electrical contact systems. It is demonstrated that the coupled electro-thermal-mechanical stresses are the primary cause of overheating

degradation of contact components

and premature failure of epoxy-impregnated paper insulation. Finally

future research directions are proposed

highlighting the need for in-depth investigation into the micro-level degradation and failure mechanisms of contact components under multi-physics coupling conditions.