TOGA

Importance of the topic

Monitoring and analysis of dissolved gases in transformer oil is critical for early detection of electrical faults in power transformers. This technique helps link gas generation profiles to specific fault types and severity levels, supporting predictive maintenance and reducing downtime.

Objectives and study overview

This application note outlines the performance of a custom configured Transformer Oil Gas Analyser (TOGA) designed to meet and exceed ASTM D3612c requirements. Key aims include demonstrating automated headspace sampling, sensitive multi-component detection, and integration with common chromatography data systems.

Methodology and instrumentation

The analyser employs closed-loop headspace sampling coupled to a single-channel GC platform.

• Gas chromatograph: Thermo Trace 1300 GC or CompactGC
• Detectors: micro-TCD for permanent gases, FID with methaniser for CO and CO2
• Autosamplers: Teledyne Tekmar Versa (20×22 ml vials) or Thermo Triplus 300 (up to 120 vials of 10–22 ml)
• Carrier gas: Argon
• Sampling principle: automated closed-loop headspace equilibration at 70 °C
• Data systems: Chromeleon, ChromCard, OpenLab, EZChrom Elite/ChromQuest
• Optional: additional gas sampling valve for direct gas injection

Main results and discussion

Analysis of standard oil samples shows detection limits substantially better than ASTM D3612c specifications:

• CO2: 0.4 ppm (ASTM 25 ppm)
• Acetylene: 0.2 ppm (ASTM 1 ppm)
• Ethylene: 0.4 ppm (ASTM 1 ppm)
• Ethane: 0.6 ppm (ASTM 1 ppm)
• Hydrogen: 2 ppm (ASTM 5 ppm)
• Oxygen and Nitrogen: < 25 ppm (ASTM 50 ppm)
• Methane: 0.2 ppm (ASTM 1 ppm)
• Carbon monoxide: 0.3 ppm (ASTM 25 ppm)

Repeatability is better than 5 % RSD at 100 ppm over at least 10 consecutive runs. The analyser achieves a full cycle time of 20 minutes and occupies a footprint of approximately 60 cm.

Benefits and practical applications

The TOGA system offers:

• Automated high-throughput analysis of up to 120 samples
• Enhanced sensitivity and dynamic range (4 decades TCD, 7 decades FID)
• Compact design suitable for onsite laboratory installations
• Compliance and superior performance relative to ASTM standards
• Seamless integration with leading chromatography software

Future trends and potential applications

Advancements may include expanded analysis of heavier hydrocarbon fragments (C3, C4), integration with remote monitoring platforms, and enhanced data analytics for predictive diagnostics. Further miniaturization and enhanced detector technologies could enable onsite or real-time transformer health monitoring.

Conclusion

The TOGA analyser represents a robust, flexible, and high-performance solution for dissolved gas analysis in transformer oil. Its superior sensitivity, automation, and compact design make it well suited for preventive maintenance programs in the power industry.

Reference

ASTM D3612 Part C: Standard Test Method for Analysis of Gases in Electrical Insulating Oil by Gas Chromatography