Seismic Isolation of High Voltage Electrical Power Transformers

Keywords: Earthquake engineering, Power Transformers, Seismic Protection, Base Isolation, Bushings Protection, Friction Pendulum Isolation, Rubber Bearing Isolation, Shake Table Experiments, Design Procedures, Computer Simulations

Abstract: This report investigates the feasibility of seismically isolating high voltage electrical power transformer structures and bushings in order to mitigate their vulnerability under strong seismic excitation.  A methodical experimental and analytical study was performed and complemented by the development of design procedures applied to an actual transformer located in the West Coast of the United States. The report first describes a shake table experimental program performed at the University at Buffalo’s Structural Engineering and Earthquake Simulation Laboratory (SEESL), which was developed to demonstrate the effectiveness of the selected isolation systems.  The testing was performed on a simulated power transformer-bushing specimen that incorporated all of the important structural features of a typical power transformer tank. Several structural variations were tested, 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, the development of numerical models of the tested frame-bushing model and the isolation systems in the commercial software SAP2000 are described, and comparisons between the numerical and experimental results are presented, to evaluate the capability of the models to predict the measured response.  Finally, based on the findings of the experimental and analytical studies, design guidelines for the base isolation of electrical power transformers are developed and summarized in the form of suggested design steps. The design of base isolation for an actual electrical power transformer, which was constructed as part of this project, is presented to demonstrate these concepts.