Analysis of Dissolved Gas in Transformer Oil by Gas Chromatography using a Stripper Column

Importance of the Topic

Monitoring dissolved gases in transformer oil is critical for early detection of electrical faults. Fault gases generated by overheating or arcing remain in the insulating fluid and, if undetected, lead to insulation breakdown, reduced performance and potentially catastrophic transformer failures.

Objectives and Scope of the Study

This work evaluates a gas chromatography approach with a stripper column, as described in ASTM D3612 Method B, for dissolved gas analysis in transformer oil (TOGA). The aims are to demonstrate detection limits, chromatographic performance and repeatability for key fault gases under realistic conditions.

Methodology and Instrumentation

The oil sample is introduced via a syringe infusion pump into two ten-port valves equipped with 100 µL loops. Each loop feeds a dedicated stripper column to extract dissolved gases, which are then routed to separate GC channels for analysis.

• Gas chromatograph: Varian 450-GC with dual-channel stripper column oven and full electronic flow control (EFC)
• Sampling system: Dual channel gas sampling valve (GSV) with luer lock connections
• Columns: CP-PoraPLOT™ U (25 m × 0.53 mm) for carbon gases; CP-Molsieve™ 5 Å (15 m × 0.53 mm) for light permanent gases
• Detectors: Flame ionization detector (FID) with methanizer for CO, CO₂ and hydrocarbons; thermal conductivity detector (TCD) for H₂, O₂ and N₂
• Carrier gases: Helium for FID channel (35.5 psi); argon for TCD channel (10.4 psi)

Main Results and Discussion

Calibration with low-concentration gas standards yielded detection limits (LDA) of approximately 4.1 ppm for H₂, 32 ppm for O₂ and 65 ppm for N₂, meeting ASTM D3612 requirements. Representative chromatograms show clear separation of H₂, O₂ and N₂ in the TCD channel and CO, CO₂, CH₄, C₂H₂, C₂H₄ and C₂H₆ in the FID channel. Repeatability experiments on an oil sample produced relative standard deviations below 1 % for most components, with slightly higher variability for CO due to lower signal intensity.

Benefits and Practical Applications

The stripper column approach enables efficient liberation of dissolved gases from oil, yielding well-resolved chromatographic peaks and accurate quantification at ppm levels. The method is suitable for both laboratory and field applications, offering robust fault gas monitoring and compliance with industry standards.

Future Trends and Applications

Integration of automated sample handling and advanced data analysis software can streamline TOGA workflows. Emerging developments include real-time online gas monitoring, enhanced column chemistries for faster separations and predictive maintenance algorithms that link gas profiles to transformer health diagnostics.

Conclusion

The described GC-stripper column method provides reliable detection and quantification of key fault gases in transformer oil, combining sensitivity, selectivity and reproducibility in line with ASTM standards. Its adaptability to field conditions makes it a valuable tool for preventive transformer maintenance.

References

• ASTM D3612-02, Analysis of Gases Dissolved in Electrical Insulating Oil by Gas Chromatography, Method B, Stripper Column Extraction, ASTM International.