Six-axis Load Head with Application to Electrical Conductor Nonlinear Dynamics

The development of a six-axis load head based on the Stewart platform concept is described in this paper. The intended application of the device is in quantifying terminal forces and moments in flexible conductors interconnecting equipment in electrical substations. Such quantification is important is assessing seismic demand both at the terminal connections and in the equipment. In particular, nonlinear effects have been observed in the dynamics of such interconnected systems, and the load head is designed to capture such effects. For this purpose, it has a large range, thus being able to record force spikes, as well as high sensitivity needed to measure low-level fluctuations that influence equipment base moments. Performance of the load head is assessed through static and dynamic tests, and implications of design modifications on performance are explored. An example application of the load head to a dynamic test is presented, where a conductor is fixed at one end and excited at the other. Results demonstrate the ability of the load head to capture nonlinear dynamic effects. Specifically, force and moment characteristics as nonlinear effects develop in the form of period-doubling are reported. A physical understanding of these phenomena is invaluable in interpreting characteristics observed in flexibly interconnected equipment.