Dissolved Gas Analysis (DGA) and Furan Analysis are the two most powerful diagnostic tools used to assess the internal health and remaining life of a power transformer.
While DGA mainly focuses on oil and electrical faults, Furan analysis evaluates the condition of paper insulation, which ultimately decides transformer life.
What is DGA (Dissolved Gas Analysis)?
DGA is a laboratory test in which transformer oil is analyzed to detect gases dissolved in it. These gases are generated due to electrical or thermal faults inside the transformer.
Internal fault → Oil & insulation breakdown → Gas formation → Oil testing → Fault diagnosis
Why DGA is Very Important?
- Detects internal transformer faults at an early stage
- Prevents sudden transformer failure
- Helps in planned maintenance
- Increases transformer service life
- Saves huge repair and replacement cost
Main Fault Gases Found in Transformer Oil
| Gas | Chemical Formula | Indicates |
|---|---|---|
| Hydrogen | H₂ | Partial Discharge |
| Methane | CH₄ | Low Temperature Heating |
| Ethane | C₂H₆ | Moderate Heating |
| Ethylene | C₂H₄ | High Temperature Overheating |
| Acetylene | C₂H₂ | Arcing Fault |
| Carbon Monoxide | CO | Paper Insulation Damage |
| Carbon Dioxide | CO₂ | Insulation Ageing |
Types of Transformer Faults Detected by DGA
1. Partial Discharge (PD)
Main gases: Hydrogen (H₂), Methane (CH₄)
2. Low Temperature Thermal Fault (Below 300°C)
Main gases: CH₄, C₂H₆
3. High Temperature Thermal Fault (Above 700°C)
Main gas: Ethylene (C₂H₄)
4. Arcing Fault (Most Dangerous)
Even a small amount of acetylene indicates a very serious internal fault.
Furan Analysis of Transformer Oil (Paper Insulation Health Test)
The core and windings of a transformer are insulated mainly with paper insulation, which is made from cellulose. Cellulose consists of long molecular chains that provide mechanical strength to the insulation.
As the transformer ages, these long chains gradually break into shorter chains due to heat, moisture, and oxidation. This phenomenon is similar to very old books, where pages become brittle over time.
Why Monitoring Paper Insulation is Critical?
In transformers, paper insulation ageing is accelerated because of continuous exposure to hot oil and oxygen. Once the paper becomes mechanically weak, it may not withstand the electromagnetic forces during short circuits.
This can result in internal electrical breakdown and catastrophic transformer failure.
Limitations of DGA for Paper Insulation Assessment
DGA provides an indirect indication of paper insulation condition using CO and CO₂ gases.
| CO₂ / CO Ratio | Condition |
|---|---|
| 4 – 11 | Healthy insulation |
| > 11 | Poor insulation condition |
However, CO and CO₂ can also be produced by oil degradation, which makes this method less sensitive and sometimes misleading.
What is Furan (Furfural) Analysis?
When paper insulation deteriorates due to destructive heating, it releases special oil-soluble compounds called Furfurals into the transformer oil.
The most important compound is 2-Furfural (2-FAL), which is generated only from cellulose degradation.
Furan compounds are NOT produced by oil ageing alone. They are a direct indicator of paper insulation damage.
Why Furan Analysis is the Best Life Assessment Test?
- Extremely sensitive – detects damage of even a few grams of paper
- Accurate for large power transformers
- Direct measurement of cellulose degradation
- Helps estimate remaining transformer life
- Most reliable test for asset management
How Furan Trend Helps Predict Transformer Life?
The gradual increase in 2-Furfural concentration over time indicates progressive ageing of paper insulation.
Trend analysis helps utilities:
- Plan refurbishment or replacement
- Avoid unexpected transformer failures
- Optimize maintenance strategy
Summary: DGA vs Furan Analysis
| Parameter | DGA | Furan Analysis |
|---|---|---|
| Main focus | Oil & electrical faults | Paper insulation ageing |
| Sensitivity | Moderate | Very high |
| Life prediction | Indirect | Direct & reliable |
Conclusion
DGA and Furan Analysis together provide a complete picture of transformer health. While DGA detects internal electrical and thermal faults, Furan analysis determines the true remaining life of the transformer.
Regular monitoring of both tests is essential for reliable and safe transformer operation.
Frequently Asked Questions (FAQ)
Q1. Is acetylene always dangerous?
Yes. Acetylene always indicates arcing.
Q2. Is Furan analysis better than DGA?
Furan analysis is best for paper insulation life assessment, while DGA is best for fault detection.
Q3. How often should Furan analysis be done?
Typically every 1–3 years, depending on transformer criticality.