The Duval triangle explained in 3 minutes
The Duval triangle is one of the most famous methods to interpret DGA results. It can be used to categorize transformer faults, based on the relative amounts of methane, acetylene and ethylene.
There are lots of tutorials available, but most of them are longer than necessary. We want to do better. So here is our quick and dirty guide to the Duval triangle. You can read it in three minutes, we promise!
Basics
Basics
The classification can be done graphically, by printing the following chart on paper.
Then use a ruler to draw a line for the relative amount of each of the three relevant gasses. All three lines should meet at one point.
The location of this point indicates the type of failure.
Example Case
Let's do an example. From a lab measurement we get the following DGA values:
- H2: 2908 ppm
- CH4: 1313 ppm
- C2H2: 8 ppm
- C2H4: 616 ppm
- C2H6: 420 ppm
- CO: 450 ppm
- CO2: 1069 ppm
We only need the values of H2, CH4 and C2H4. The other values are not used in the Duval triangle method.
Example Calculation
Example Calculation
The percentage of H2 is 2908/(2908 + 1313 + 616) = 0.601 = 60.1%.
The percentage of CH4 is 1313/(2908 + 1313 + 616) = 0.271 = 27.1%.
The percentage of C2H4 is 616/(2908 + 1313 + 616) = 0.127 = 12.7%.
The corresponding lines are drawn parallel to the labelling of the axes.
The point of intersection lies in the area called D1, meaning low energy discharge, or sparking.
Failure Codes
The complete list of failures codes can be seen here:
- PD: partial discharge
- T1: thermal fault below 300 degrees celcius
- T2: thermal fault between 300 and 700 degrees celcius
- T3: thermal fault above 700 degrees celcius
- D1: low energy discharge (sparking)
- D2: high energy discharge (arcing)
- DT: mixture of thermal and electrical faults
Note how every possible combination of DGA values will result in a failure classification. There is no area designated as normal.
The duval triangle can only be used for fault classification, but not for fault detection. In other words: Before doing any of this, be sure that your transformer is actually faulty.
