The research presents a thorough investigation into critical aspects of transformer insulation and advanced condition monitoring techniques aimed at sustaining reliability. Key challenges in maintaining efficiency, such as partial discharge, are addressed by adopting methodologies like ultra-high frequency and fluorescent optic fiber techniques. Additionally, the study explores the impact of Fuller earth reclamation treatment to extend the lifetime of the multi-stressed aged transformer oil, utilizing physico-chemical analysis for condition monitoring the status of insulation structures. Furthermore, insights into nanofluid-based transformer oil flow characteristics and significant enhancements in dielectric performance are indicated. Overall, this research significantly advances the understanding of transformer insulation materials and detection methodologies, promising enhanced reliability and efficiency in service.