Microstructure Evolution Study of the Field-Serviced Silicone Rubber Insulator via X-Ray Micro-CT Imaging

Composite silicone rubber insulators are widely used in overhead transmission lines but undergo inevitable aging-induced performance degradation or failure. Understanding their aging process is crucial for optimizing manufacturing and on-site service, yet studies on microstructural changes-especially three-dimensional (3D) microstructural evolution during aging-remain scarce. This study employed X-ray micro-computed tomography (X-ray micro-CT) to characterize and compare the 3D microstructure of one fresh and one field-serviced composite silicone rubber insulator (which underwent 10 years of outdoor service). For the field-serviced insulator, key findings include the following: (1) pore number decreased (from 2200 to 1600), while pore size increased (equivalent diameter: from 3.5 ± 1.3 μm to 10.4 ± 7.2 μm); (2) porosity increased (from 0.04% to 0.69%); (3) new cracks formed (length: 100-900 μm); and (4) pore shape remained nearly unchanged relative to the fresh sample. Notably, the aging depth of the field-serviced insulator was less than 300 μm. These results clarify the 3D microstructural evolution of composite silicone rubber insulators during aging, providing a basis for improving their long-term reliability.