An Analysis of Power Transformer Failures using the Mixed Weibull Statistics

A method for evaluating replacement life of substation transformers required to build an asset management system is presented. The electrical utilities are replacing the transformers at the time when the failure rate of the transformers increases to prevent sudden failures. In this study, the mean time to failure of the transformers was defined as the technical end of life, and 52 years was calculated by analyzing the cumulative density function of the failure data. The replacement time of the transformers was defined as the strategic end of life, and 32 years was calculated by failure rate (Bathtub curve) analysis. These lives of the substation transformers are calculated based on 154kV three-phase transformers with sufficient failure data, and the lives of 154kV single-phase transformers applied since 1995 should be recalculated when failure data is sufficiently collected. In addition, the replacement life of the transformers should be strategically decided according to the business value of the company and the risk associated with the failure of the transformer.