This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

In the preparation process for laboratory seismic testing of instrument transformers, accurately determining the mechanical properties of all materials used in their key components is particularly important. This becomes even more critical when FEM (Finite Element Method) dynamic analysis is conducted as part of the preparation. Knowing the precise mechanical properties of these materials ensures reliable modeling, allowing for more accurate predictions of the transformer's performance under seismic conditions. Instrument transformers play a crucial role in transformer stations, serving as indispensable components for the reliable operation of power systems. As such, their design must address not only electrical performance requirements but also mechanical robustness. Proper dimensioning of these transformers is essential to withstand the maximum mechanical stresses they may encounter during their operational lifespan, especially in regions prone to seismic activity. To meet the requirements set forth in IEEE 693-2018, thorough preparation is necessary. This involves conducting FEM analyses to determine the natural frequencies, evaluate the maximum stresses in critical areas, and dimension the transformer'™s key components, such as the tank of the electromagetic unit and insulators of the capacitor divider. While generic mechanical properties are typically sufficient for isotropic materials, orthotropic materials, like composites, present a unique challenge. Their complex mechanical behavior requires extensive testing to accurately define their properties. In most cases, data provided by composite manufacturers is used to address this gap. This paper presents the seismic testing of two capacitor voltage instrument transformers, performed according to IEEE 693-2018, and analyzes the obtained results. A detailed analysis of the influence mechanical properties of all used materials have on the results of FEM analysis was conducted after the seismic tests. The study investigates the discrepancies observed between the natural frequencies, stresses, and deformations identified in the pre-test FEM analysis and those measured during laboratory testing. By incorporating a range of mechanical properties into a post-test FEM analysis, new results were generated and compared with shake table test outcomes. These comparisons provided critical insights into the underlying causes of the discrepancies and led to a conclusive evaluation of the transformers'™ seismic performance. After testing, a DoE (Design of Experiments) analysis of the transformer's natural frequencies was conducted using a wide range of key mechanical properties to identify the causes of the discrepancies between the natural frequencies measured during the test and those predicted by the pre-test FEM analysis. A sensitivity analysis was performed, and a response surface was generated. Presented results provided critical insights into the underlying causes of the discrepancies and led to a conclusive evaluation of the transformers'™ seismic performance.