Design of Flexible Cable Installations within Congested Tunnel Systems

HV and EHV cables associated with the new SGTs will also be replaced. New customer connections and distribution cables will also be installed within the wider project. At the date of publishing, the cable system installation is planned for Q2 2026.

The substation, first constructed in the 1960’s, uses a network of cable tunnels to interconnect transformer enclosures and switch houses. The majority of the cables installed within the tunnels feature oil filled insulation and PVC oversheaths, any failures would result in dangerous conditions, where confined space working procedures apply.

To reduce the requirement for confined space working, a “3D point cloud” has been captured of the tunnel network, which has then been converted into a BIM model. This model has been used for the coordination of all circuits undergoing replacement, incorporating 3rd party design works. This “Digital First” approach to the design of the replacement cable works significantly reduced the amount of access required to the tunnel.

The new cables will be approximately 60% larger than the existing ones, the challenge was to design a rigid and/or flexible systems that would not interfere with the existing cables. Flexible systems were developed that generated between 81% and 95% lower thermomechanical forces, requiring between 38% and 62% less steelwork, than the equivalent rigid systems.

The main methods used in the design of the flexible cable system were based on CIGRE

Technical Brochures (TB) 194 [1] and 669 [2]. The “western” method for vertically sagged cable systems were considered, and the Arc-Castigliano method, traditionally used for flexible loops approaching terminations, was applied to flexible bends around right-angled corners.