Duval’s Triangle 2 was developed by Michel Duval for diagnosing potential faults due to the complex mechanical and electrical operations in Load Tap Changer (LTC) in mineral oil.

Since tap changers are subject to electrical switching operations, they are prone to faults like arcing and partial discharges. Analyzing the dissolved gases in the oil using Duval’s Triangle 2 helps in early detection and maintenance planning.

The three dissolved gases that make up Duval’s Triangle 2 are Methane (CH₄), and Ethylene (C₂H₄) and Acetylene (C₂H₂) arranged in a ternary plot similar to Duval’s Triangle 1 as depicted in Figure 1 below [1]. These are the same combustible gases as used in the Duvals Triangle 1 but the fault regions are now different.

The fault regions are :

• N – Normal Operation
• T2 – Severe thermal fault T2 (300 °C < T < 700 °C), coking
• T3 – Severe thermal fault T3 (T > 700 °C), heavy coking
• X3 – Fault T2 or T3 in progress with light coking or increased resistance of contacts, or severe arcing D2
• D1 – Abnormal arcing D1
• X1 – Abnormal arcing D1 or thermal fault in progress

The one precondition is that fault diagnosis should not be done if the concentrations of C₂H₂ and C₂H₄ are below 10 ppm [1].

Analyse your Tap changer Oil Sample below:

Duvals Triangle 2

Methane (CH₄):

Ethylene (C₂H₄):

Acetylene (C₂H₂):

Plot

References

1. M. Duval, “The duval triangle for load tap changers, non-mineral oils and low temperature faults in transformers,” in IEEE Electrical Insulation Magazine, vol. 24, no. 6, pp. 22-29, November-December 2008, doi: 10.1109/MEI.2008.4665347.