Categorizing transformer faults via dissolved gas analysis

The industry at large is very proficient at diagnosing temperature within a power transformer via Dissolved Gas Analysis (DGA) and there are many tools to assist in this process, such as Duval's Triangle, Rogers Ratio, etc. However, identifying categorically where the overheating is taking place continues to remain relatively a mystery, for the most part. It is also noted that there have been some transformers which have suffered a winding failure with no historical DGA overheating prior to failure via routine sampling, or violation of industry standard CO ppm values. This is not to say that overheating didn't occur prior to failure, but rather the last manual sample collected did not reveal any overheating and the problem seemed to develop so quickly that the outage came as a surprise to all. It is the intent of this paper to demonstrate a method utilizing the historical CO₂/CO ratio in mineral oil filled transformers to help solve these puzzles and do it with greater accuracy than previously believed possible. By trending the CO₂/CO ratio, the user will be able to qualify problems with heavy paper (such as a winding), light paper (such as a lead) and bare-metal connections (such as a De-Energized Tap Changer).