Seismic isolation of electrical transformers
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High voltage transformers are pieces of equipment essential for the operation of a power system. Together with high voltage bushings, which are critical components for their functionality, they have been shown to be particularly susceptible to damage during past strong earthquakes. In this work, base isolation is proposed and studied as a practical means of seismically protecting and retrofitting high voltage transformers and their appendages. Due to the differences between transformers and conventional engineering structures, the design of seismic isolation systems for high voltage transformers is controlled by specific parameters. Such parameters involve the requirement for small isolator displacements due to the limited slack of high voltage conductors connected to the transformer and flexibility of connections to other ancillary equipment, limitations in the attachment method of the isolators to the transformer to facilitate installation, highly asymmetric distribution of mass and stiffness of typical transformer tanks, and the relatively light weight of transformers. In light of these constraints, two systems are selected in this work as the best candidate systems for the seismic isolation of electrical transformers: (a) stiff and highly damped Lead-Rubber Bearings (LRB), and (b) high friction Triple Friction Pendulum (Triple FP) bearings. This dissertation presents a shake table experimental program at the Structural Engineering and Earthquake Simulation Laboratory at the University at Buffalo, performed to demonstrate the effectiveness of the selected isolation systems. Testing was performed on a simulated transformer-bushing specimen - which nonetheless incorporated all of the important structural features of a typical transformer tank - and for several structural variations including isolated and non-isolated conditions, variation in the installation of the isolators, use of scaled and actual size isolators in testing, and different mounting configurations for the bushing. Furthermore, this dissertation describes the development of numerical models of the tested frame-bushing model and the isolation systems in the commercial software SAP2000, and presents comparisons between the numerical and experimental results, to validate the capability of the models to predict the measured response. Finally, based on the findings of the experimental and the analytical studies, design guidelines for the base isolation of electrical transformers are summarized in the form of suggested design steps, and the design of base isolation for an actual electrical transformer is presented for demonstration of these concepts.