Analytical and Experimental Seismic Studies of Transformers Isolated with Friction Pendulum System and Design Aspects

Abstract

This paper presents the results of analytical and experimental studies on the use of an advanced technology for seismic rehabilitation and design of substation transformers. The isolation system, known as Friction Pendulum System (FPS), combines the concepts of sliding bearings and pendulum motion. Discussion of formulation is followed by an extensive parametric study using a typical transformer. Among parameters are peak ground acceleration, bidirectional motions, effect of vertical motion, and isolation radius. Inertia reduction and the maximum displacement of the system are the criteria used in evaluating the seismic response and the effectiveness of FPS bearings. Using the results of the parametric study, charts that can be used in design are developed for each criterion. Furthermore, two commonly used response combination rules, namely SRSS and CQC, are evaluated, and recommendations are made with regard to the suitability of each method in estimating the total responses under orthogonal motions. Finally, the results of an experimental study, which considers 1-D, 2-D, and 3-D responses of fixed and base isolated transformer models supporting a bushing, are presented. Experimental results are consistent with the analytical results and further support the effectiveness of FPS bearings in reducing inertia forces, thus, providing a suitable procedure to mitigate the seismic hazard of substation transformers.