Power transformers are key foundational equipment for stable power distribution and electrical isolation in power systems. Long-term operational overload, insulation aging, internal discharge and local overheating will induce latent faults, which easily trigger sudden equipment failure and power outages without early monitoring. Dissolved Gas Analysis (DGA) based on gas chromatography is the most authoritative and mainstream non-destructive detection technology for transformer internal fault diagnosis. It can accurately capture early latent faults that cannot be identified by conventional electrical tests. In daily operation and maintenance, regular chromatographic detection is essential for both large grid transformers and small and medium-sized distribution equipment. The isolation distribution transformer, widely used in industrial and civil power isolation scenarios, relies heavily on gas chromatography detection to eliminate internal hidden dangers. Similarly, the 50 kva single phase transformer, commonly applied in household, commercial and scattered load power supply scenarios, also needs standardized oil gas monitoring to ensure long-term safe and stable operation.
JINSHANMEN TECHNOLOGY CO., LTD is a professional manufacturer of full-series power power transmission and distribution equipment. The company mainly produces oil immersed power transformers, dry-type power transformers, oil-immersed three-dimensional wound core transformers, dry-type three-dimensional wound core transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on-load voltage regulating transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind farm box substations, high and low voltage switchgear and other power transmission and distribution equipment. The company's self-developed and manufactured isolation distribution transformer and standardized 50 kva single phase transformer adopt high-purity insulating oil and optimized internal insulation structure. Combined with standardized factory detection and on-site operation and maintenance specifications, the equipment effectively reduces gas dissolution risks and improves operational stability.
Ⅰ. Correlation Between Transformer Dissolved Gas and Internal Faults
Transformer insulating oil undertakes two dual critical functions of internal insulation and circulating heat dissipation. When internal overheating, partial discharge or arc discharge faults occur, insulating oil and solid insulation materials will undergo thermal decomposition and chemical cracking, producing a variety of characteristic gases, including hydrogen (H₂), carbon monoxide (CO), carbon dioxide (CO₂), and hydrocarbon gases such as CH₄, C₂H₆, C₂H₄, C₂H₂. The type, concentration and generation rate of these gases are directly correlated with fault temperature and fault severity.
With the continuous rise of fault temperature, the precipitation order and concentration of hydrocarbon gases change regularly. CH₄ and C₂H₆ are mainly produced in low-temperature overheating faults, while C₂H₄ dominates in high-temperature overheating conditions, and C₂H₂ is the typical characteristic gas of discharge faults. Most of the decomposed gases dissolve in the insulating oil, and a small amount of free gas accumulates in the gas relay. By analyzing gas components and content changes, operation and maintenance personnel can accurately judge the fault type, development stage and risk level.
Combined with long-term operational data summary, the corresponding relationship between characteristic gas parameters and typical transformer faults is summarized as follows:
1. General overheating fault: The total hydrocarbon content is slightly high, the C₂H₂ concentration is lower than the 5μL/L warning value, the fault develops slowly, and the gas production rate is stable at a low level, belonging to early latent fault.
2. Severe overheating fault: The total hydrocarbon content rises significantly, C₂H₂ may exceed the warning value but does not dominate the total hydrocarbon components, accompanied by a sharp increase in H₂ content and accelerated gas production rate.
3. Partial discharge fault: The total hydrocarbon content is normal, H₂ concentration exceeds the 150μL/L warning standard, and CH₄ accounts for the main proportion of total hydrocarbons.
4. Spark discharge fault: Total hydrocarbon content is stable, C₂H₂ and H₂ concentrations increase significantly, and C₂H₂ content is usually higher than 10μL/L.
5. Arc discharge fault: Total hydrocarbon content surges, C₂H₂ becomes the dominant component of hydrocarbon gases, and both C₂H₂ and H₂ contents far exceed the standard values, belonging to dangerous sudden faults.
Ⅱ. Advantages and Limitations of Gas Chromatography Fault Diagnosis
Transformer gas chromatography detection extracts oil samples from operating equipment, separates and analyzes dissolved gases in insulating oil through professional chromatographic instruments, and realizes quantitative and qualitative judgment of transformer operating status and fault types. This technology is an indispensable core method of transformer condition-based maintenance in the power industry.
The core advantage of gas chromatography analysis is early warning of latent faults. Most thermal and discharge faults inside transformers will not cause obvious changes in electrical parameters in the early stage, and conventional electrical protection tests cannot identify hidden dangers. However, gas chromatography can capture trace gas changes in the early stage of fault occurrence, effectively avoiding equipment burnout, power failure and other major accidents. For widely used power distribution equipment such as isolation distribution transformer and 50 kva single phase transformer, regular chromatographic detection can form a reliable operational safety guarantee.
Meanwhile, gas chromatography technology has certain application limitations. The dissolved combustible gas in transformer oil has complex sources. Chromatographic data can only judge the fault nature and severity, but cannot pinpoint the exact faulty component or fault location. Single chromatographic analysis is prone to misjudgment, leading to unnecessary maintenance operations. Therefore, fault diagnosis must be combined with transformer structure characteristics, operational history and conventional electrical test data to form comprehensive and accurate judgment results.
Ⅲ. Key Precautions for Gas Chromatography Fault Analysis
Transformer dissolved gas content is affected by multiple factors such as internal faults, equipment structure, installation process, external environment and manual operation. In actual detection and analysis, external interfering factors must be ruled out first to avoid misjudgment of equipment operating status.
First, eliminate non-fault gas interference. Common interference sources include oil tank welding with oil, unqualified supplementary insulating oil, oil leakage of on-load tap-changers, residual gas after equipment installation and maintenance, unstandardized oil sampling operation, instrument detection errors, equipment dampness and oil flow electrification. These factors will lead to abnormal gas indicators, which are easily misjudged as internal overheating or discharge faults. For this reason, standardized construction, strict oil quality inspection and complete degassing treatment are essential in equipment installation, maintenance and operation.
Second, adopt dynamic tracking monitoring. Once chromatographic data is abnormal, the fixed detection cycle shall be cancelled, and intensified tracking detection shall be carried out. Fault judgment cannot rely on single test data. It is necessary to compare historical data, summarize gas change trends and gas production rates, and dynamically evaluate fault development trends to determine whether the equipment needs to be shut down for maintenance.
Third, prioritize early warning signals of discharge faults. C₂H₂ is a typical characteristic gas of discharge faults. Even if its concentration is lower than the 5μL/L warning value, continuous growth or excessive gas production rate indicates potential discharge hidden dangers. To avoid sudden arc faults and power supply interruption, the equipment shall be shut down immediately for inspection when the cause cannot be confirmed.
Fourth, adopt multi-dimensional collaborative diagnosis. Chromatographic analysis results must be combined with electrical test data, relay protection action records, equipment operating environment, load changes and abnormal operating sounds for comprehensive judgment. Magnetic circuit overheating, conductive circuit faults and insulation faults often have cross manifestations, and multi-dimensional verification can effectively improve fault positioning accuracy.
Fifth, standardize fault judgment criteria for gas relays. When the light gas protection acts and free gas accumulates in the gas relay, oil sample chromatographic analysis must be carried out immediately. Colorless, odorless and non-combustible gas is usually residual air generated by incomplete degassing after oil injection or oil pump seal failure; odorous and combustible gas indicates internal equipment faults, which requires immediate shutdown and comprehensive troubleshooting.
Sixth, ensure the accuracy and reliability of test data. Testers shall strictly implement preventive test specifications and chromatographic analysis guidelines. For equipment with rising gas indicators, shorten the detection cycle for tracking; for equipment with low total hydrocarbon content, avoid misjudgment by relative gas production rate; newly commissioned transformers must retain pre-operation baseline data to provide accurate support for subsequent fault analysis.
Ⅳ. Conclusion
Gas chromatography dissolved gas analysis is the key technical approach for transformer latent fault early warning and quantitative diagnosis. It makes up for the deficiencies of conventional electrical tests and provides reliable support for transformer condition-based maintenance and safe operation. In actual operation and maintenance, standardized sampling, scientific data analysis and multi-dimensional joint judgment are required to eliminate misjudgment risks. Adhering to refined operation and maintenance management can effectively extend the service life of isolation distribution transformer, 50 kva single phase transformer and various power transmission and distribution transformers, and ensure the stable and safe operation of the entire power distribution system.