Mechanical Properties Evolution and Aging Mechanism of NBR Sealing Materials Under Multiple Environmental Factors in Ultra-High Voltage Converter Station

Nitrile butadiene rubber (NBR) is commonly served as a sealing element for oil-tight seals in ultra-high voltage converter stations. Due to the harsh environmental conditions in these stations, NBR is frequently exposed to thermal oxidation, ultraviolet radiation, and low temperatures, as well as the effects of the sealed medium. This work focuses on evaluating the impacts of various environmental conditions on the mechanical characteristics of NBR and analyzes the underlying mechanisms. Stress distribution under the combined action of force, heat and hypothetical electric field is analyzed with the aid of ABAQUS simulation; the aging test only investigates single factors without verifying the multi-field coupling mechanism, and the conclusions are only for qualitative reference of the simulation. The service life of NBR is effectively predicted based on the compression set decay curve. Analysis of TGA measurements reveals the gradual loss of incorporated additives upon aging, accompanied by a reduction in the thermal stability of aged NBR. Results from crosslinking density tests, FTIR, and XPS analyses demonstrate that oxidation crosslinking progressively increases as thermal-oxidative aging proceeds, the rise in C–C and C–H content is associated with the degradation of C=C bonds, oxygen-containing functional groups (carboxyl, hydroxyl, and carbonyl) are generated during the thermal-oxidative aging of NBR, and the cleavage of C–S bonds leads to the formation of S=O species.