# Seismic Vulnerability Assessment of Hybrid Mold Transformer Based on Dynamic Analyses
## 1 Introduction  
Over the last few decades, strong earthquake ground motions have caused severe physical and functional damage not only to structural systems, but also to nonstructural elements, which have in turn led to major operational failures and economic losses in radical buildings, and special facilities such as hospitals, high-tech laboratories, power stations, and nuclear power plants. Among the various types of nonstructural elements, critical functional components such as electrical systems have been shown to cause major economic losses inside buildings during earthquakes [1; 2; 3; 4]. Previous earthquake events including the 1994 Northridge earthquake in Los Angeles, the 2008 Great Sichuan Sichuan earthquake in China, the 2010 Maule earthquake in Chile, and the 2010 Sierra El Mayor earthquake in Mexico have shown that 25,230 kV transformers are particularly vulnerable to earthquake damage in major buildings [5]. Recently, in South Korea, the 2016 Gyeongju and 2017 Pohang earthquakes caused significant deterioration to nonstructural electrical elements inside critical public buildings such as hospitals, Korea train express (KTX) railway stations, high schools, broadcasting stations, and shopping malls [6]. Therefore, seismic vulnerability assessment and safety evaluation of electrical elements have come to be recognized as key topics in the framework of earthquake risk mitigation. In order to investigate the behavior and vulnerability of structural and nonstructural elements under realistic earthquakes, experimental earthquake simulation methods such as shaking table tests have been used by several previous research studies [7; 8; 9; 10; 11; 12; 13; 14; 15]. These shaking table tests could enable more realistic simulation and performance assessment of nonstructural elements. Nevertheless, the empirical data obtained from the test results can only be applied to limited regions for which the correlation between the dynamic response of nonstructural elements and characteristics of the earthquake isclearly tested. Thus, numerous shaking table tests using input ground motion that covers a large range of magnitudes as well as frequency content are necessary. Moreover, due to the variety in the specifications, configurations, support boundary conditions, and manufacturers of the nonstructural elements, in particular the electrical facilities in buildings, a limited number of shaking table tests could not provide sufficient information to assess the seismic vulnerability of the nonstructural elements. Accordingly, in order to comprehensively investigate the vulnerability of such nonstructural elements, reliable dynamic analyses could be used with intensive input earthquake ground motions. To date, several studies have been conducted using analytical models to evaluate the seismic vulnerability of nonstructural elements, including mechanical and electrical facilities subjected to earthquake load. [PERSON] et al. (2016) assessed the seismic vulnerability of a 400 kV power transformer (PTR) by using 3D finite element modeling and time history analysis. In total, 99 tri-axial accelerograms of ground motions were considered as the input base excitations in the model of PTR. Seismic analytical fragility curves of PTR were obtained in two damage states using the Multiple Stripes Analysis approach to minimize the required number of structural analyses. The results indicated that this technique was efficient and that the analyses could be targeted at a limited number of important intensity measurement (IM) levels, as opposed to requiring analyses at all high or low IM levels. [PERSON] (2017) assessed the seismic response and vulnerability of switchboard cabinets mounted on building floors by using nonlinear numerical models. The main purpose of this study is to generate simplified numerical models of the switchboard cabinets using finite element (FE) methods to investigate the seismic behavior during earthquake events.