Modified Dissolved Gas Analysis Scoring Approach for Transformer Health Evaluation Considering Delta and Rate Values of Dissolved Gases in Mineral Oil

Transformers are among the most important components in the energy grid due to their missions and high costs. The challenging operating conditions deteriorate their components and shorten the life of the transformers. The health index approach is a critical and effective method for monitoring transformers in the operating environment, early diagnosis of possible malfunctions, and evaluation of their general condition. DGA, OQA, and PIF parameters, which represent the condition of the insulation materials, which mainly determine the life of transformers, constitute the basic inputs of the health index approach. In this study, a new method was proposed to determine the DGAF score based on the dissolved gases in mineral oil. With this method, in addition to the delta and rate values of the gases, the past DGA results of the transformer were also considered in determining the DGAF. In this way, faults experienced during operation are included in the health index calculation. The proposed method was tested using 36 DGA results obtained over a period of approximately 10 years from a transformer operating in the grid. The obtained results are presented in comparison with the traditional DGAF scoring method.