Aging diagnosis of solid insulation for large oil-immersed power transformers

Furfural analysis has been proved a useful tool for the aging diagnosis of solid insulation in large oil-immersed power transformers. Up-to-now, diagnostic criteria for operating transformers are in urgent need. In the investigation, quite a lot of data have been collected, such as the furfural concentrations, service durations, water contents, etc. To reveal the relationship between furfural contents in oil and the aging condition of solid insulation, statistic analyses are carried out. Then, the factors affecting the aging process such as service duration is studied. Therefore, the statistic distribution of furfural concentration in oil is worked out. According to the theoretical distribution, several warning levels of furfaral in oil could be calculated, which are more reasonable than that the regulation had recommended. An example of practical application shows it is effective and easy to apply for operating transformers.