Graphical Shape in Cartesian Plane Based on Dissolved Gas Analysis for Power Transformer Incipient Faults Discrimination

Dissolved Gas Analysis (DGA) is a technique, which is more frequently employed in power transformers to assess the incipient faults that are developed in oil-immersed transformers. Duval triangle-I is the simplest methodology for dissolved gas analysis to evaluate the incipient faults. In addition, it is more accurate than other conventional methods like Doernenburg, Roger’s, and IEC techniques. The main disadvantage of conventional methods is their inability to identify a large percentage of fault cases. However, Hydrogen (H
₂
) concentration, which is crucial for diagnosing various faults, particularly low temperature thermal fault and partial discharge, was not considered in the Duval triangle-I method. Rather, only three gases, which are Methane (CH
₄
), Ethylene (C
₂
H
₄
) and Acetylene (C
₂
H
₂
), are used in Duval triangle-I method. Consequently, this paper introduces a new graphical method for power transformer incipient faults discrimination based on three new ratios of gases that consider the concentration of Hydrogen (H
₂
) and the influence of Ethane (C
₂
H
₆
). These three ratios are converted to a point (x, y) in the cartesian plane. Based on the position of this point within the new graphical shape, the type of incipient fault is determined with an accuracy reaching 92%. A practical DGA database is collected from different transformers in service and IEC TC 10 database and used to evaluate the accuracy of this method. Additionally, various incipient faults are experimentally simulated in the laboratory and their results are utilized in the proposed method. This methodology aims to overcome the drawbacks of Duval triangle-I and other conventional methods. The results ensured that the proposed graph provides better diagnosis accuracy when compared to Duval triangle-I and other techniques.