Non-Invasive Structural Retrofit of an Existing Dead-End Tower for Cable Terminations and Surge Arresters in a Scandinavian Substation

This paper presents the structural design and assessment of a non-invasive retrofit solution for an existing dead-end tower in a Scandinavian substation. The tower serves as the transition point between an overhead line (OHL) and underground cable systems, and was required to accommodate new cable terminations, surge arresters, and associated conductor supports as part of an OHL extension. The primary engineering challenge arose from the need to install additional equipment on a legacy structure without modifying the original tower members by welding or drilling. The proposed solution consisted of custom-designed support frames and brackets attached using existing holes in the tower legs. To satisfy electrical clearance requirements, the equipment was installed at a specified inclination through specially configured support channels and adaptor arrangements. Structural analysis was performed using a finite element modelling approach, with beam and plate elements used to evaluate the supporting frame and critical connection components. The design considered dead load, conductor tension, wind load, ice and snow load, mechanical operation load, construction and maintenance load, temperature effects, and short-circuit force. Ultimate and serviceability limit state combinations were assessed in accordance with relevant Eurocode provisions. Member utilization, plate stresses, bolt interaction ratios, and weld capacities were verified and found to satisfy the design criteria. The study demonstrates a practical methodology for the functional upgrading of existing substation interface structures while preserving structural integrity, minimizing outage duration, and maintaining compliance with electrical and mechanical performance requirements.