A transformer failure rate model concering aging process and equipment inspection data

This paper proposes a new oil-immersed transformer failure rate model based on Cox´s time-dependent proportional hazards model (PHM). The proposed model takes both equipment aging process and equipment inspection information into consideration. The failure rate function of PHM consists of two parts: the baseline hazard function which represents the aging process, and the link function which represents the influence of covariant, such as the equipment health condition. In the proposed model, the baseline hazard function follows a winding hot spot temperature-based aging model. The quantity of the dissolved gas in oil is used to estimate the equipment health condition which is used as the covariate of the link function. The probability density function (PDF) of the time to failure is determined, and the maximum likelihood estimation (MLE) is used to estimate the unknown parameters. The case study shows that the proposed model is able to reflect the individual variation and customize the transformer failure rate reasonably and comprehensively. In addition, the maintenance effect can also be taken into account.