Monitoring Hydrogen and Methane Gases in Transformer Oil Using Palladium and Polydimethylsiloxane Coated Fiber Bragg Grating Sensors

This study presents Fiber Bragg Grating (FBG) sensors coated with palladium (Pd) and polydimethylsiloxane (PDMS) for detecting dissolved hydrogen (H₂) and methane (CH₄) in transformer oil, key indicators of incipient transformer faults. Laboratory evaluations covered concentrations of 5–2146 ppm for H₂ and 3–1551 ppm for CH₄ at 10–90°C. Gas-induced Bragg wavelength shifts were validated against Dissolved Gas Analysis (DGA) using the Transport X system. The Pd-coated H₂ sensors achieved sensitivities of 0.000487 nm/ppm with 97.04% accuracy and 0.000451 nm/ppm with 99.953% accuracy, while PDMS-coated CH₄ sensors reached 0.00591 nm/ppm with 95.85% accuracy and 0.00226 nm/ppm with 95.03% accuracy. All sensors exhibited strong linearity (R² > 0.91) and excellent repeatability (RSD < 1% above 40 °C). Temperature compensation models were developed to ensure accuracy under varying operational conditions. Compared with previously reported optical gas sensors, the proposed Pd- and PDMS-coated FBG sensors demonstrate superior sensitivity, broad detection range, thermal stability, and cost-effectiveness. These features make them highly promising for real-time, in-situ monitoring of dissolved gases, enabling advanced fault diagnosis and condition-based maintenance in power transformers.