Brechin-Fiddes 132kV OHL Undergrounding

Innovative design of bespoke cable termination structure

Reducing outage requirements and carbon footprint of construction programme

Cost and time savings through optimised construction programme and material usage

Safeguarding operations

SSEN had identified a safety hazard in the Brechin to Fiddes 132kV overhead line, where an adjacent farm operation yard had, over the years, expanded under the existing route. This meant that raw materials were being stored directly beneath the overhead line, and personnel and heavy machinery were passing through the same area. To avoid electrical safety clearances being breached and to maintain the integrity of the power supply, SSEN opted to underground this 570 metre section of the line.

BakerHicks was appointed to carry out the detailed design for the project, including all cabling and overhead line design services:

  • Electrical design and layout of the HV route
  • Supporting calculations for the underground cable pulling and installation
  • Design of the overhead line’s (OHL) modifications
  • Structural design and foundation design for OHL structures
  • Design of the earthing system

Bespoke solutions

Bespoke design solutions enabled continuity of electricity supply on demand, reducing outages and network risk throughout construction. Incorporating a 250 metre Horizontal Directional Drill (HDD) section under the farm allowed the yard to be kept operational throughout the works.

A temporary diversion was originally proposed, however, through further analysis of the scope of works and pre-construction information our engineers mitigated the need for the costly diversion of the overhead line. They designed a bespoke wooden cable termination structure to support the underground cable terminations. Designed with cross-arms that could support post insulators whilst the underground cable route was being built, the new terminal poles could be constructed under the existing line and the conductors transferred to the posts’ insulators. This ensured that the overhead line remained functional throughout construction and could be re-energised at any time without the need for a temporary diversion. 

Minimising environmental impact

A sustainable and highly innovative solution, the environmental impact of the project was minimised through restricting the new underground cable route to the original footprint of the overhead line and the elimination of the need for a temporary diversion. This meant the original wayleaves agreement was adhered to, whilst the amount of waste material produced during the construction programme was reduced.

Completed to schedule, the undergrounding of the 132kV overhead line ensured a sustainable and cost-effective solution. Seamless construction and installation meant that electricity supply remained continuous without disrupting the surrounding infrastructure and businesses, including the farm.