Health index for power transformer condition assessment based on operation history and test data

Abstract

Transformers are key equipment in a power grid. The stability of the power system is depending more and more on the safety and reliability of transformers. Health Index (HI) is a practical tool that combines complex condition data into a single value as a comparative indication of the overall condition of a transformer. Most of the existing health index procedures are based on laboratory or on-site test data, with few considering the actual operating time. In this research, a comprehensive assessment method of transformer operating condition is proposed. Based on the HI model, this method the first considers the aging process of the transformer insulation as well as the load and operating environment to form the theoretical health index HI1. The aging process is characterized by the operating time of the transformer, the load rate, and the pollution level. The test health index HI2 is then formed based on on-site tests. The final health index HI is obtained with the combination of HI1 and HI2 to characterize the health condition of the transformer. To make sure the proposed method can be readily adapted in the field, only traditional parameters with well-established interpretations are required. This method has been applied to assess multiple 330kV transformers in service and provided a useful method to transformer asset management.