Application of Insulation Aging Evaluation Method for Distribution Transformers in Practice

Status evaluation of transformer insulation aging is an important issue. The key to solving the problem is to find electrical or physicochemical characteristic features or evaluation method which can effectively reflect the status of transformer insulation aging. Usually, experimental tests are conducted to achieve this target. Although the testing method can directly indicate the loss of insulation life, it is expensive and restricted by the actual working conditions. This method is mainly used for the power transformers in the main power networks, but it is difficult to be widely used for the distribution transformers (DT) due to larger amount and limited maintenance budget. In order to find a suitable method for insulation aging evaluation of DT, the thermal circuit model method is used to calculate the hot-spot temperature that can reflect the aging rate of the transformers. According to the data quality, operating environment and operating state of the DT, the traditional thermal circuit model is optimized to improve the accuracy in this paper. Moreover, the data collected from on-service DT are used to verify the feasibility and effectiveness of this model. Results show that this method can effectively indicate the loss of insulation life for DT. Compared with the measure of operating years, the result of the model can more closely reflect the actual aging statues of DT. More importantly, the method provided in this paper is able be widely used for the evaluation of DT insulation in practice.