Continued operation of critical lifelines after a major earthquake is essential for reduction of losses, timely delivery of emergency services, and post-earthquake recovery. An important element within the power transmission lifeline is the electrical substation, which serves to transform the power voltage for distribution in local grids. The electrical substation typically consists of a complex set of equipment items that are interconnected through either assemblies of rigid-bus and flexible connectors or through flexible cable conductors.
Estimating the seismic response and reliability of an electrical substation is a challenging task because (1) connected equipment items cannot be analyzed individually due to the presence of their dynamic interaction; (2) the connecting elements (either rigid-bus flexible connector or flexible cable conductor) behave nonlinearly; (3) the earthquake ground motion is stochastic in nature; and (4) the substation is a complex system subjected to a stochastic loading for which reliability cannot be directly dedu ced from the marginal reliabilities of its components. This re- port aims at developing analytical models a nd methods for assessing the seismic response of electrical substation equipment connected by asse mblies of rigid-bus and flexible connectors, and the reliability of electrical substation systems subjected to stochastic earthquake loading. A parallel aim is to develop practical guidelines for the design of connected equipment items to reduce the adverse effect of dynamic interaction under earthquake loading. Attention is also given to developing systematic methods for identifying critical components and cut sets within the electrical substation system.
An electrical substation equipment item is idealized as a single-degree-of-freedom oscillator by describing its deformation in terms of an assumed displacement shape function. The validity and accuracy of this idealization for interaction studies is examined for an example pair of connected equipment items. The hysteretic behaviors of several rigid-bus connectors are described by differential equation mode ls fitted to experimental data or to hysteresis loops predicted by detailed finite element analysis. Efficient nonlinear time-history and random vibration analyses methods are developed for determining the seismic response of the connected equipment items. Based on the developed analytical mode ls and methods, the effect of interaction in the connected equipment system is investigated through extensive parametric studies. The results lead to practical guidelines for the seismic design of interconnected
electrical substation equipment.
In order to estimate the seismic reliability of the electrical substation system, linear programming is used to compute bounds on the system reliability in terms of information on marginal- and joint-component failure probabilities. This methodology is also used to systematically identify critical components and cut sets within the electrical substation system. Finally, to apply this methodology to the electrical substation sy stem under stochastic earthquake loading, new formulations and results are developed for the joint first-passage probability of a vector process. Example applications are used throughout the report to demonstrate the newly developed models and methods.
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