DGA–Duval Triangle Analysis for Early Thermal Fault Diagnosis of Transformer Oil

Abstract

This study assesses the health of the T5 transformer oil at the Geothermal Power Plant to enable early thermal-fault diagnosis and support evidence-based maintenance. Methods comprised Dissolved Gas Analysis (DGA) with TDCG evaluation per IEEE C57.104-2019, Duval Triangle mapping, and breakdown-voltage (BV) and water-content testing per IEEE C57.106-2015. Results show TDCG of 686 ppm (Condition 1) with CO₂ at 10,000 ppm; gas fractions CH₄ 70.18%, C₂H₄ 29.24%, and C₂H₂ 0.58% place the point in zone T2 (300–700 °C). Water content is 29 ppm—above the recommended limit for transformers <72.5 kV (good: <10 ppm)—while mean BV is 73.4 kV, exceeding the 40 kV minimum. The evidence indicates a medium-level thermal fault with high moisture contamination. Oil filtering/dehydration and periodic DGA trend monitoring are recommended to mitigate failure risk and inform data-driven maintenance planning