Dynamic reliability analysis of the bushings’ base fracture of a 220 kV transformer-bushing system subjected to fully nonstationary earthquake loads

Abstract

The high-voltage (HV) transformers, primarily composed of the oil tank and porcelain bushings, are vulnerable to earthquake damage and prone to fracture at the base of the porcelain bushings. The dynamic reliability analysis of HV transformer bushing base fracture involves calculating the small first passage probabilities for nonstationary wide-banded random seismic responses exceeding the high threshold levels. Existing methods for addressing this issue are either inefficient or impractical. To efficiently estimate the small first passage probabilities, this paper proposes a tail decay rate and multiple support points-based shifted generalized lognormal distribution (SGLD) model method. The method formulates the parameter estimation for the SGLD as an optimization problem with a constraint, enabling rapid parameter estimation. To implement, the objective function is formulated to minimize the mean absolute percentage error of failure probabilities, incorporating multiple support points to enhance the comprehensive utilization of simulation samples. Furthermore, the constraint is introduced concerning the hypothesis of near-linear behavior in the tail region corresponding to small failure probabilities, wherein the slope of the asymptotically correct first passage probabilities calculated by the crossing approach approximates the actual slope. The dynamic reliabilities of the porcelain bushings’ base fracture of a 220 kV auto-transformer subjected to the fully nonstationary El-Centro-like earthquake load are analyzed utilizing the proposed method. The analysis demonstrates the application process and efficiency of the proposed method and provides seismic design recommendations for this kind of transformers.