Mixed-Discrete optimization of spacer configuration for Short-Circuit force reduction in EHV bundled conductors

Short-circuit events in extra-high-voltage (EHV) air-insulated substations produce strong electrodynamic forces on flexible bundled conductors, resulting in high tensile stress, pinch interaction between sub-conductors, conductor swing, and possible reduction in phase-to-phase clearance. In such cases, the system’s reaction depends on spacer span, spacer mass, and bundle spacing, determining the system’s equivalent mass and dynamic behavior. In this study, the governing force is defined as the maximum value among the tensile, drop, and pinch forces, which must be minimized while satisfying mechanical and clearance constraints. Given the discrete nature of design variables, this is a nonlinear and mixed-discrete optimization problem. The resulting problem is formulated as a nonlinear, constrained, mixed-discrete optimization problem in which spacer span, spacer mass, and bundle spacing are optimized simultaneously. A hybrid CSS-EM solver is adopted as the computational optimizer for the proposed mixed-discrete formulation. The main novelty of the work lies in the spacer-configuration optimization formulation rather than in the development of a new metaheuristic algorithm. A practical 220 kV case study shows the existence of a complex and nonlinear design space with transition zones where the governing force mechanism changes. Existing standards such as IEC 60865 and IEEE Std. 605 provide procedures for short-circuit-force calculation; however, they do not explicitly consider spacer-configuration optimization. The proposed methodology addresses this design gap.