Dissolved Gas Analysis (DGA) is an important technique in transformer maintenance. One of the most well-known DGA interpretation methods is the Duval Triangle, developed by Michel Duval of Hydro-Québec. This method simplifies the identification of internal transformer faults based on the composition of three main gases. This article provides a quick and practical guide to understanding and using the Duval Triangle.

What is the Duval Triangle?
The Duval Triangle is a triangular diagram used to determine the type of fault in a transformer based on the ratio of three dissolved gases:
- Methane (CH4)
- Acetylene (CH2H2)
- Ethylene (CH4)

These three gases are the result of thermal and electrical breakdown within the transformer. By plotting the relative percentages of each gas within the Duval Triangle, users can quickly identify the likely fault type.

Fault Types Based on the Duval Triangle
The Duval Triangle divides the triangular area into several zones, each representing a specific type of fault, including:
- PD (Partial Discharge) – partial discharge
- D1 and D2 (Low/High Energy Discharges) – electrical surges
- T1, T2, T3 (Thermal Faults) – thermal faults with low to very high temperatures
- DT (Mix of Electrical and Thermal Faults) – a combination

Steps for Using the Duval Triangle
1. Perform a DGA to obtain the concentrations of CH4, C2H2, and C2H4 (in ppm).

2. Calculate the total of the three gases.

3. Convert to a percentage: CH4% = CH4 x 100%, C2H2%, C2H4%
                                                           Total

4. Plot the values on the Duval triangle diagram.

5. Identify the zone where the point falls to determine the fault type.

Advantages of the Duval Triangle Method
- Fast and easy to use
- Statistically proven and widely used
- Assists in early diagnosis without the need to dismantle the transformer
- Suitable for predictive maintenance

Limitations of the Duval Triangle
- Only uses three main gas types
- Less suitable if all gases are at low levels
- Interpretation can be biased if there is sampling error

The Duval Triangle method is a simple yet powerful diagnostic tool in DGA analysis. By understanding the patterns and zones within this triangle, technicians can quickly identify potential faults in transformers and take preventive action before major damage occurs.

Mastering the Duval Triangle is a crucial step in building an efficient and reliable condition-based maintenance program for your electrical system.