Seismic failure risk analysis of ± 800 kV coupling filter circuit considering material strength deviation

Abstract

To analyze the seismic failure risk of an 800 kV filter circuit, which is a coupling system consisting of a series of interconnected post electrical equipment and a suspension filter in an ultra-high voltage converter station, dynamic calculations were performed using a 3D finite element model. Using three different probabilistic approaches based on equipment fragility curves generated by fitting log-normal distributions, the seismic fragility of the coupling filter circuit was calculated. Furthermore, the seismic failure risk of the circuit was evaluated utilizing the seismic hazard function of the site and the circuit fragility function. As a significant factor, the impact of material strength deviation on seismic fragility and failure risk was then investigated. The analytical results highlight three essential seismic responses: the root stress of post insulators, disconnect switches, and the axial stress of top suspension insulators. For equipment, post insulators always exhibit the highest vulnerability in the circuit. Compared to the approach employing the fragility definition, the equipment probability deduction approach estimates exorbitant circuit fragility while the maximum probability method slightly underrates it. A safe region exists on the failure risk surface, where the circuit failure risk is near 0. In particular PGA ranges, material strength deviation can remarkably increase the seismic fragility and failure risk of the coupling filter circuit. Consequently, it is recommended to regulate material strength deviation during the design phase to seismically protect the coupling circuit.