Experiences with transformer diagnosis by DGA: case studies

Power transformers are key apparatuses in power delivery, and due to this fact, several diagnostic methods have been established for it. Dissolved gas analysis (DGA) is a chemical diagnostic tool, which plays an important role in the industry since it can detect a transformer fault in the early stages and save the transformer from consecutive major failures. In this study, after reviewing the significant points in the DGA procedure, five real cases are reported which explain the transformer diagnosis by DGA. In all these cases, DGA plays a key role while other diagnostic tools such as measuring the winding DC resistance, tan δ, dielectric resistance etc. are also employed to discover the problem. In the final part, a fuzzy softening method combined with evidential reasoning is proposed to ease the DGA interpretation for the less expert technicians. This method amends and combines standard methods and does not need a training phase. In summary, the experiences shared in this study can help the industry personnel dealing with transformers to diagnose a transformer problem with more expertise.