A new graphical technique for the interpretation of dissolved gas analysis in power transformers

Duval triangle for dissolved gas analysis (DGA) in power transformers was frequently used due to its simplicity. However, Duval triangle did not consider the concentrations of Ethane (C₂H₆) and Hydrogen (H₂) in spite of their importance in diagnosing certain types of faults. Accordingly, in this paper, a new graphical technique for DGA was developed considering all five combustible gases. The proposed graphical technique was built using a pentagon shape with its heads representing the percentage concentration of each individual gas to the total combustible gases. The corresponding point for each case was determined by the center of mass of these percentage concentrations. First, the knowledge related to each fault type was extracted from previous DGA methods as well as from field experience. Then, this knowledge was used to estimate the preliminary positions of boundaries between fault regions within the pentagon. Finally, the exact boundaries between fault regions were proposed by plotting actual DGA data with corresponding fault types collected from the Egyptian Electricity Network. The comparison with Duval triangle showed that the proposed pentagon shape has good diagnosis accuracy.