Probabilistic Resilience Assessment of Electrical Substations

@mastersthesis{rustamy2022,
  title = {Probabilistic Resilience Assessment of Electrical Substations},
  author = {Rustamy, Abdul},
  year = {2022},
  month = may,
  publisher = {Lehigh University},
  keywords = {Data Science, Probabilistic modeling, Probabilistic restorations, Resilience, simulation, Statistical analysis},
  abstract = {Electric power systems are the backbone of urban societies and their continued functionality after a major seismic event is essential to reduce financial losses, time to restore emergency services, and time to post-earthquake full recovery. Electrical power substations are important subsystems within electric power systems used to transform voltage levels within the system. Loss of substation functionality disrupts the distribution of the electric power, leading to power outages; extended loss of functionality may cause significant economic and social losses. This dissertation research investigates the seismic resilience of electrical substations, including the hazard, substation component damage, substation functionality loss, and system functionality restoration using a probabilistic approach.The research objectives are: (1) to assess natural hazards that may impact electrical substations with emphasize on the seismic hazard; (2) to develop seismic damage fragilities of substation components, such as transformer, disconnect switch and circuit breaker; (3) to evaluate the seismic functionality fragility of substations (as systems); (4) to obtain substation component functionality restoration data through expert interviews and surveys, and use these data to develop substation system functionality restoration curves; (5) to assess the seismic resilience of electrical substations and demonstrate the entire assessment process using two example substations. To reach these objectives, the research uses finite element structural analysis models, state-of-the-art simulation methods, expert interviews, and an expert survey. The hazard assessment is implemented through literature review, evaluation of historical damage, expert interviews, and probabilistic simulations. Earthquakes and flooding are found to be the two dominant hazards that affect electric power system substations. Seismic (earthquake) loading has caused widespread structural damage to substation components. The Lehigh Valley (in Pennsylvania, USA) is treated as a testbed for developing seismic hazard data and for a substation resilience assessment. To represent the seismic hazard, site-specific ground motions are generated using a stochastic simulation method. It was found that the types of grounds motions used in fragility analyses of substation components significantly impact the results; using site-specific ground motions should be considered when the site class and site seismicity information are known. Flooding and storm surges cause substations to be shut down until substation components are cleaned from moisture and debris. Due to the high weight-to-volume ratio and physical profiles of typical substation components, there has not been historical damage to them from hydrostatic and buoyancy forces. The functionality of a substation depends on the functionality of the individual substation components (disconnect switches, circuit breakers, and transformers) and the redundancies present in the substation. Seismic damage fragility curves are developed for substation components at the 230 kV and 500 kV voltage levels using finite element models and dynamic analyses. Then, a simulation method is presented for the seismic functionality fragility analysis of an electrical substation which uses the seismic damage fragilities of the substation components as input. Although redundant current paths within the substation may increase the probability of substation functionality after component damage from short circuit events or internal component electrical failures, it is found that redundant current paths may improve probability of substation functionality during a more widespread event such as seismic loading only if the component failure events are not highly correlated. The functionality restoration time after a damaging seismic event depends on the number of non-functional or damaged components, the availability of resources, and the rapidity of the disaster-response team. There is limited information and data about the functionality restoration of electrical substations and components. An online expert survey and expert interviews were conducted to bridge this knowledge gap and collect functionality restoration data for individual substation components. Then a simulation method is presented to compute the substation functionality restoration using the substation component functionality restoration. Finally, the substation component damage fragility, substation system functionality loss, and seismic functionality restoration results are combined to describe the resilience of electrical substations using a simple resilience index. As case studies, the seismic resilience of two substations at the 230 and 500 kV voltage levels is assessed. The results of this study are expected to be useful to electrical utility companies, disaster managers, insurance companies, and government entities in assessing the seismic resilience of electrical substations as systems.},
}