Duval Triangle Method for Power Transformers Diagnostic

Duval triangle method – is a graphic method of transformer defect nature determining.

This diagnostic method was developed in 1974 by well-known Canadian specialist M. Duval. Duval triangle method allows to plot the point on the graph based on the values of the concentrations of three gases (C2H2, C2H4, CH4), represented as a triangle. The triangle area, according to the Duval method, is divided into seven zones. Each zone corresponds to a certain defective condition of the transformer. In total, seven defective states are considered. By belonging of a point to a particular zone, the type of defect is determined. Duval triangle is equilateral. The relative content value of a certain gas is plotted on each side, that can be changed from 0 to 100% clockwise. In this case, the sum of the gases concentration values of all is taken as 100%, and the concentration percentage of each gas is determined from this sum. When drawing the boundaries of defect zones, the lines are drawn parallel to the lagging side of the triangle, i.e. if the point is taken on the CH4 side, then the line from this point runs parallel to the C2H2 side, if the point is taken on the C2H4 side, then it is parallel to the CH4 side, etc. As a result of the constructions, the Duval triangle is obtained.

In the practical use of this method, it is necessary to find the percentage of each gas, set it aside on the corresponding side of the triangle, and draw three lines from each point parallel to the lagging side, which will intersect at one point. The location of this point will determine the zone and the diagnosed defect.

Theconsidered method not only clearly shows the “place” of the defect, but also allows you to observe the trajectory of its development, when after a certain time several chromatographic analyzes of dissolved gases are made and the resulting points are successively plotted on a triangle.

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