What is Duval's Triangle?
Duval's Triangle is a graphical method for interpreting Dissolved Gas Analysis (DGA) data in power transformers. It plots three hydrocarbon gases as relative percentages on a ternary diagram and classifies the transformer's operating condition based on which region the data point falls in.
What is Dissolved Gas Analysis (DGA)?
Dissolved Gas Analysis is a diagnostic technique that measures the concentrations of gases dissolved in transformer insulating oil. When a transformer experiences a fault — electrical or thermal — the oil and paper insulation decompose, releasing characteristic gases. By analysing the types and quantities of these gases, engineers can identify the nature and severity of the fault without taking the transformer offline.
The Three Gases
Duval's Triangle specifically uses three hydrocarbon gases:
| Gas | Formula | Primary Indicator Of |
|---|---|---|
| Methane | CH4 | Low-temperature thermal faults and partial discharges |
| Acetylene | C2H2 | Electrical discharges (arcing and sparking) |
| Ethylene | C2H4 | High-temperature thermal faults |
How the Triangle Works
- Normalise concentrations. The three gas concentrations are converted to relative percentages that sum to 100%.
- Plot the point. The normalised values are plotted on a ternary (triangular) plot where each corner represents 100% of one gas.
- Identify the fault region. The location of the data point on the triangle determines the fault classification based on empirically defined region boundaries.
Why Duval's Triangle?
Duval's Triangle is one of the most widely used DGA interpretation methods globally. It is recommended by major standards organisations and transformer manufacturers for several reasons:
| Method | Visual | Standardised | Easy to automate |
|---|---|---|---|
| Duval's Triangle | Yes | Yes | Yes |
| IEC Ratio Method | No | Yes | Yes |
| Key Gas Method | Yes | No | No |
| Roger's Ratio | No | Yes | Yes |
The visual nature of Duval's Triangle makes it particularly useful for communicating findings to non-specialist stakeholders, while standardised region boundaries ensure consistent results across analysts and laboratories.
Why Plotly for Duval's Triangle?
This library uses Plotly as its plotting backend because:
- Interactivity. Plotly figures are zoomable, hover-enabled, and support real-time panning — ideal for examining dense data points.
- Notebook support. Plotly renders natively in Jupyter notebooks without additional plugins.
- Web export. Figures can be saved as standalone HTML files, embedded in web pages, or exported as PNG/SVG images.
- Programmatic control. Every aspect of the plot can be customised through Python code, making it suitable for automated reporting pipelines.
Relationship to Transformer Diagnostics
Duval's Triangle is part of a broader DGA workflow. It is typically used alongside other diagnostic methods such as gas ratio analysis, key gas analysis, and furan analysis to build a comprehensive picture of transformer health. Regular DGA monitoring using Duval's Triangle can detect developing faults months or years before they lead to failure, enabling condition-based maintenance and reducing unplanned outages.