Combined Duval Pentagon Method for Transformer Fault Diagnosis

Introduction

Transformers are essential components of electrical power systems, and ensuring their reliability is critical for maintaining a stable power supply. One of the most effective techniques for monitoring the health of oil-filled transformers is Dissolved Gas Analysis (DGA). DGA involves analyzing the gases dissolved in the transformer’s insulating oil, which are generated as byproducts of various fault conditions. By interpreting the concentrations of these gases, engineers can identify potential issues before they lead to significant failures.

Among the various methods available for interpreting DGA results, the Duval Pentagon stands out as a robust and intuitive graphical tool. It complements traditional approaches, such as those outlined in IEEE and IEC standards, by providing a comprehensive way to visualize and diagnose faults using five key hydrocarbon gases: hydrogen (H₂), methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂H₂). This article explains the Duval Pentagon method in a straightforward manner and highlights the advantages of its upgraded version, the Combined Duval Pentagon.

The Duval Pentagon Method

The Duval Pentagon method is designed to interpret DGA results by representing the relative contributions of the five main hydrocarbon gases in a pentagonal chart. Here’s how it works conceptually:

• Relative Percentages: The process begins with measuring the concentrations of the five gases in parts per million (ppm). The relative percentage of each gas is then determined by dividing its concentration by the total sum of all five gas concentrations. For instance, if hydrogen is measured at 50 ppm and the total concentration of all five gases is 200 ppm, hydrogen’s relative percentage is 25%.

  
  

• Graphical Representation: These percentages are plotted on a regular pentagon, where each vertex corresponds to one of the five gases. Each axis extends from the center of the pentagon (representing 0% of that gas) to the vertex (representing 100% of that gas). However, in practice, the scales are adjusted so that the maximum value along each axis is effectively 40%, due to the way the method interprets the data.

  
  

• Centroid Location: The five percentage points form an irregular pentagon within the regular one. The centroid, or the “center of mass” of this irregular shape, is identified. This centroid’s position within the pentagon is what indicates the type of fault present in the transformer.

  
  

• Fault Zones: The pentagon is divided into distinct zones, each corresponding to a specific fault type. These zones are established based on extensive data from transformers with known faults, confirmed through visual inspections. The main fault types include:

  
  

  • PD (Partial Discharges): Corona discharges that indicate minor insulation issues.

  • D1 (Low Energy Discharges): Electrical discharges of lower intensity.

  • D2 (High Energy Discharges): More severe electrical arcing.

  • T1 (Thermal Faults < 300°C): Low-temperature thermal issues.

  • T2 (Thermal Faults 300–700°C): Moderate-temperature thermal faults.

  • T3 (Thermal Faults > 700°C): High-temperature thermal faults.

  • S (Stray Gassing): Gas production not related to faults, often due to oil aging or minor thermal stress.

Figure 1. Duval Pentagon method (a) original regular Pentagon, formed by the five combustibles (b) Duval Pentagon 1, showing the fault zones as described above. Cheim (2020).

Initially, the Duval Pentagon method was introduced in two versions:

• Pentagon 1: This version identifies the basic fault types listed above (PD, D1, D2, T1, T2, T3, and S). It provides a broad overview of the transformer’s condition.

  
  

• Pentagon 2: This version offers a more detailed classification, particularly for thermal faults. It categorizes them into:

  
  

  • T3-H: High-temperature faults in oil only.

  • C: Thermal faults involving carbonization of paper insulation (across T1, T2, or T3 ranges).

  • O: Overheating below 250°C without carbonization.

  • S: Stray gassing, as in Pentagon 1.

  • PD: Partial discharges, as in Pentagon 1.

  • D1: Low Energy Discharges, as in Pentagon 1.

  • D2: High Energy Discharges, as in Pentagon 1.

Figure 2. Shaded areas Illustrating differences between (a) thermal zones T1, T2 and T3 in Pentagon 1 (b) thermal zones O, C and T3-H in Pentagon 2. Cheim (2020).

While both pentagons are effective, using them separately requires interpreting two distinct graphical representations, which can complicate the diagnostic process.

Advantages of the Combined Duval Pentagon

The Combined Duval Pentagon is an innovative upgrade that merges the strengths of Pentagons 1 and 2 into a single Pentagon. This enhancement offers several significant benefits:

1. Simplified Analysis:

   The combined pentagon reduces the total number of fault zones from 14 (when using Pentagons 1 and 2 separately) to 10. The common zones (PD, S, D1, and D2) remain unchanged, while the thermal fault zones are integrated into a more streamlined classification:

   
   

   • T1-O: Overheating below 300°C without carbonization.

   • T1-C: Thermal fault below 300°C with carbonization.

   • T2-O: Thermal fault 300–700°C without carbonization.

   • T2-C: Thermal fault 300–700°C with carbonization.

   • T3-H: High-temperature fault in oil only (> 700°C).

   • T3-C: High-temperature fault with carbonization (> 700°C).

   
   

   This reduction simplifies the interpretation process, making it easier to apply in practice.

   
   

2. Computational Efficiency:

   By using a single geometry instead of two, the combined pentagon streamlines the computational effort required for automated fault identification. This is particularly advantageous for software applications and computer programs that analyze DGA data, as they no longer need to handle two separate pentagon structures with different zone boundaries.

   
   

3. Retained Detail:

   Despite the simplification, the combined pentagon preserves the critical ability to distinguish between thermal faults with and without paper carbonization. For example, identifying whether a T2 fault (300–700°C) involves carbonization (T2-C) or not (T2-O) is vital, as paper degradation can signal a more severe issue requiring urgent action. This detailed classification ensures that the method remains diagnostically robust.

   
   

4. Enhanced Usability:

   Engineers and maintenance personnel can obtain a comprehensive fault diagnosis from one graphical tool, eliminating the need to cross-reference between Pentagons 1 and 2. This improves efficiency and reduces the potential for errors in interpretation, especially under time-sensitive conditions.

   
   

5. Support for Decision-Making:

   The combined pentagon provides clear, actionable insights. For instance, a diagnosis of T3-C (high-temperature fault with carbonization) indicates a serious condition involving the transformer’s solid insulation, prompting immediate investigation or removal from service. Conversely, T3-H (oil-only fault) might suggest a less critical issue, allowing for different maintenance strategies.

Figure 3. Final geometriy of the newly Combined Pentagons. The 10 zones are PD, S, D1, D2, T1-O, T1-C, T2-O, T2-C, T3-C, T3-H. Cheim (2020)

The combined pentagon does not replace the original Pentagons 1 and 2 but complements them by offering a unified approach that balances simplicity with detailed fault identification. It is particularly valuable for users who need to classify all 10 fault types efficiently, as recognized in standards like IEEE C57.104-2019.

Note: It is not recommended to attempt fault identification using the method described above if all gas levels are below the values of IEEE Std C57.104-2019 Table 1.

Conclusion

The Duval Pentagon method is a powerful tool for diagnosing transformer faults through DGA, offering a visual and intuitive way to interpret the relative concentrations of key hydrocarbon gases. By plotting these concentrations on a pentagonal chart and identifying the centroid’s position within predefined fault zones, engineers can pinpoint issues ranging from electrical discharges to thermal faults.

The Combined Duval Pentagon enhances this method by integrating the capabilities of the original Pentagons 1 and 2 into a single, streamlined geometry. It simplifies the diagnostic process, improves computational efficiency, and retains the detailed classification necessary for effective decision-making—all without sacrificing accuracy. This upgrade makes the Duval Pentagon method more accessible and practical for modern transformer maintenance, supporting the reliability and longevity of these critical power system assets.

Our Solutions

The HV Assets Care Platform is a complete solution for data analysis and diagnostics. It includes all the recommended methods from the IEEE standard, including the Duval Triangle and the advanced Combined Duval Pentagon (as below figure), integrated in a asset management dashboard. In addition, provides a Health Index with individual scores to create an asset ranking. For more information, click here.

Combined Duval Pentagon, an advanced feature included in our HV Asset Care platform.

References

1. CIGRE, "Guide for transformer maintenance" (445), 2015.

2. Cheim, Luiz, Michel Duval, and Saad Haider. 2020. "Combined Duval Pentagons: A Simplified Approach" Energies 13, no. 11: 2859. https://doi.org/10.3390/en13112859

3. M. Duval and L. Lamarre, "The duval pentagon-a new complementary tool for the interpretation of dissolved gas analysis in transformers," in IEEE Electrical Insulation Magazine, vol. 30, no. 6, pp. 9-12, November-December 2014, doi: 10.1109/MEI.2014.6943428.