Structural design and seismic qualification of extra high voltage disconnect switch

Abstract

This paper describes the structural design approach and the method of seismic qualification for an extra high voltage disconnect switch, a vital component in the substations of a power system network. Shaping and sizing of porcelain members of the frame received special attention to enhance their resistance to earthquake. A carefully developed finite element model, on analysis by response spectrum and time-history methods, showed acceptable seismic performance and an adequate margin of safety. Shake table tests for seismic qualification, called for by the specification, were not feasible owing to the large dimensions of the complete assembly. The alternative approach was to perform in situ modal tests. By exciting the structure with a random force through a portable hydraulic exciter and using accelerometers to record the structural response, the dynamic characteristics of the equipment — the frequencies, mode shapes, and damping — were determined. Correlation between the results of finite element analysis and experimental modal analysis confirmed the validity of the analytical model. Application of combined analysis and testing for seismic qualification is demonstrated by a case study on an 800 kV disconnect switch.