<![CDATA[Power transformers are essential components of electrical power transmission systems, where insulation deterioration and operational aging can compromise reliability and increase the risk of failure. Comprehensive condition assessment is therefore necessary to support effective maintenance planning and enhance transformer asset management. This study aims to assess the condition of power transformers using a Health Index (HI) approach that integrates electrical and insulation diagnostic parameters. The study was conducted on 14 power transformers installed at 150-kV transmission substations. The assessment incorporated several diagnostic parameters, including dissolved gas analysis (DGA), moisture content, acidity, interfacial tension, breakdown voltage, insulation resistance, dielectric dissipation factor (tan ?), winding resistance, and sweep frequency response analysis (SFRA). These parameters were integrated into five assessment factors: internal fault indicators, paper insulation condition, insulating oil quality, electrical insulation condition, and winding condition. The results indicated that four transformers were classified as Very Good, four as Good, three as Fair, and three as Poor. Furthermore, the analysis revealed a negative relationship between transformer service age and HI values, with a coefficient of determination (R²) of 0.7793, suggesting a strong association between aging and transformer condition. Field verification confirmed that the HI classifications were consistent with the transformers' actual operating conditions and diagnostic findings. This study demonstrates that the proposed HI method provides a comprehensive and practical framework for assessing transformer condition, supporting more effective condition monitoring, preventive maintenance planning, and informed decision-making in power system asset management.]]>
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