Seismic behavior analysis of electrical substation system by frequency response curves

A complete laboratory-based seismic testing is the ideal standard qualification method to determine the amplified response accelerations of the electric power utility equipment. As an alternative to the complete experimental procedures, an analytical methodology with partial experimentation is proposed to assess the structural performance prior to the seismic qualification experiments in the present analogy. The proposed approach is based on the free vibration tests conducted at manufacturing unit, an analytical study of acceleration transmissibility and phase shifts of individual modes of the structure. This method also focuses on understanding the state of the system at post resonance. Different types of substation equipment are analyzed for the dynamic response and a case study of 36 kV circuit breaker is presented in this work. Harmonic vibrations of 0.2 g ground accelerations applied to index the modal parameter i.e., damping ratios at corresponding natural frequencies. Force transmission and phase lag at individual modes of the system opposing random ground accelerations are computed. The plots of frequency response curves of majority of the tested substation equipment showed the response acceleration is low at higher frequency ratios. Also, the response acceleration is not influenced by damping of the structure in the region of high frequency ratios. The presented methodology reduces the experimental complexities in the laboratories and the final qualification can be done in single attempt.