An Improved ASTM D3612 TOGAS System

Significance of the Method

Analyzing dissolved gases in transformer oil is essential for assessing the health and integrity of high-voltage equipment. ASTM D3612 provides a standardized approach for quantifying hydrogen, oxygen, nitrogen, methane, carbon monoxide, carbon dioxide and light hydrocarbons. Enhancing sensitivity and broadening the detectable gas range improves early fault detection and supports preventive maintenance in power utilities and industrial settings.

Objectives and Overview

This study aimed to refine the ASTM D3612 TOGAS system by replacing the traditional thermal conductivity detector (TCD) with a Barrier Ionization Discharge (BID) detector and by incorporating propane and butane into the analysis. Key goals included lowering hydrogen detection limits from 10 ppm to 100 ppb and enabling a single-detector solution for all target gases.

Methodology and Instrumentation

The modified method employed two PLOT columns in series: a 30 m×0.53 mm Carboxen-1006 column for CO₂ and C₂–C₃ hydrocarbons, and a 30 m×0.53 mm SH-RT-MSieve 5A column for H₂, O₂, N₂, CH₄ and CO. A four-port stream selection valve directed early eluting components to the BID detector and later components through a methanizer to an FID. Key instrumental details:

• Gas Chromatograph: Shimadzu GC-2010 Plus Tracera equipped with BID-2010 Plus
• Detector Conditions: BID at 200 °C, He discharge gas 50 mL/min; FID at 200 °C, H₂ 65 mL/min, air 400 mL/min, makeup He 20 mL/min
• Injection: Direct mode, 100 °C injector, 110 kPa initial pressure ramping to 150 kPa
• Oven Program: 70 °C for 2.8 min, ramp to 95 °C at 40 °C/min, ramp to 150 °C at 7 °C/min
• Methanizer: 380 °C conversion of CO₂ to CH₄ for FID detection

Main Results and Discussion

The BID detector achieved over 100× the sensitivity of TCD and twice that of FID for universal detection. Hydrogen was quantified at 100 ppb, and methane and carbon monoxide were resolved with low background noise. Repeatability studies (n=4) showed relative standard deviations below 10 % for all analytes. Propylene was successfully detected at a retention time of 15 min, and butane could be analyzed with extended run times.

Benefits and Practical Applications

The improved TOGAS system offers:

• Enhanced sensitivity for early fault gas detection
• A single detector platform simplifying hardware configuration
• Robust long-term stability via dielectric barrier discharge design
• Flexible analysis including light olefins and paraffins

Future Trends and Applications

Integration of headspace autosamplers (e.g., HS-20, HS-10) can automate sample introduction per ASTM D3612 Method C. Advances may extend detection to heavier hydrocarbons (C₄–C₆), incorporate multi-dimensional GC separation, and develop portable field deployable systems. Software enhancements and machine learning could further improve automated fault diagnosis.

Conclusion

The substitution of a BID detector and the inclusion of propane and butane expanded the analytical scope and improved detection limits of ASTM D3612. The revised TOGAS system demonstrates high sensitivity, reproducibility and operational simplicity, making it well suited for routine transformer oil monitoring and gas analysis in electrical equipment diagnostics.

References

• Wang Z “Max”, Smith M, Taylor CM. An Improved ASTM D3612 TOGAS System. Pittcon 2016.