Investigation on the Diffusion Characteristics of Dissolved Gas in an Actual 400 kV Converter Transformer—Effects of Fault Types

The dissolved gas analysis (DGA) technology is a key method for monitoring large oil-immersed transformers. However, the large size, complex structure, and extended gas diffusion paths of high-capacity transformers make the diffusion characteristics of fault-generated gases within the transformer unclear, which limits the detection accuracy of DGA technology. This article investigates the diffusion characteristics of dissolved gases in a ±400 kV converter transformer under various fault types and analyzes the temporal changes in gas concentration at different monitoring points during the diffusion process. The results show that oil flow velocity is the primary factor influencing the diffusion of dissolved gases in the transformer. Although the concentration of fault gases does not affect the diffusion path of dissolved gases in the transformer, it does influence the diffusion rate. Moreover, the oil flow circulation at the turret on the ac side of the converter transformer is slow and directional, which impedes the diffusion of dissolved gases in the transformer oil, thereby hindering timely fault detection. The results of this study offer significant insights for the installation of dissolved gas monitoring devices in field converter transformers and the determination of the optimal monitoring cycle interval.