Structural characteristics linked performance assurance in alumina based porcelain insulators

Usage of electricity in every segment of daily life has led to increased requirements with regard to performance of insulating materials in general, and specifically porcelain insulators. This has dictated the need to study issues related to the ceramics for attaining high levels of reliability. Materials characteristics such as structural phases, microstructure, composition, inclusions, porosity and homogeneity play a dominating role in arriving at the right combination of properties required for performance as well as life of the insulators. A study has been conducted on a set of alumina insulators at various stages of installations in the specific application of 25 kV railway traction lines, where they are subjected to electrical stresses, vibrations and adverse environmental conditions. It includes new insulators, failed within a few months during service and dismounted from line after several successful years of service. A distinct correlation between the total alumina content, % (α-Al₂O₃ (corundum phase), % α-quartz, mullitic regions, uniformity in chemical composition with respect to micro-structural features and porosity has been evolved. Influences of particle fineness, aspects of aging, correlation between alumina content and mechanical properties have also been included in the study. The exhaustive data generated and the conclusions drawn have been supported by usage of X-ray Diffraction for structural phase studies, microstructure, chemical composition, crack propagation and defect morphology studies by Scanning Electron Microscope, micro-hardness and fracture toughness analysis. Information on specific factors influencing performance and failure mechanisms, emphasizing the importance of the few but critical material characteristics that affect the reliability of alumina insulators is presented.