Estimation of displacement at interconnection points of substation equipment subjected to earthquakes

This paper presents a simple and useful method to estimate the expected displacement at the interconnection point of substation equipment under seismic excitation. Analysis and a survey of qualification reports on standalone equipment revealed that for many types of equipment, the displacement is composed almost entirely of the contribution of the first vibration mode. The generalized single-degree-of-freedom method is therefore recommended to evaluate the displacement, using the first modal-participation factor and the spectral displacement from the required response spectrum. Mean and bound values of this factor were determined and are presented. Shake table tests were performed to investigate the effect of the flexible connection on this factor. It was found that, when sufficient slack is provided, its main effect, on average, is to decrease the standalone modal-participation factor.