Case Study: X Routes – 400kV Modernisation

SCOPE Line Modernisation inc Condition Assessment & LiDAR
Dec 2019 to March 2021


The X routes are an uprated 400kV steel lattice tower line of L2 (Contract T-1011) design that forms an interconnection located to the east of Scotland within the central belt. The line originates at XM001, consisting of 165 double circuit towers of L2 design. The X routes consist of four routes: XD, XN, XK and XM Route, erected in the 1960s. Each had been constructed with twin bundled phase conductors 2x400mm² ACSR Zebra and had a 175mm² ACSR Lynx earthwire. At XN route There were poor ground conditions along the route and 80% of the route has special foundations.

The modernisation works covered full insulator changeout, full condition assessment on all routes and OPGW restringing on XM route. A full condition assessment and associated steelwork detailing and installation undertaken which included a foundation condition assessment made up of a parts. Part 1 was a desktop study using BGC maps, and loads from the modelling. Part 2 was a site walkover a soil sampling of highly utilised foundations to determine site specific conditions and whether further investigation was required.


Groundline Liaised with the contractor to successfully delivery catenary support system (CSS) protection designs for 31 spans, with 38 obstacles requiring a 12 week lead to deliver designs for 7 railways and an A-road


Groundline where instructed by a contractor to undertake the full construction design requirements associated with the scope of works. The scope included the requirement to work closely with a contractor and SPEN to focus on modernisation of the existing line.

The operations the Groundline team had to perform in order to deliver the scope included:

• PLS-TOWER and PLS-CADD Modelling
• Structural Analysis, Strengthening and Design
• Clearance Reporting and Mitigation
• Geotechnical Analysis & QRA
• Insulator Drawings
• Wire Clearance Diagrams
• Full fittings replaced
• Profiles
• Sag & Tension
• Full Temporary Works, Rigging, Construction and Maintenance Design
• Aerial Catenary Support System Design
• Full Climbing Condition Assessment
  • Line Diagrams
  • Bar Replacement Schedule
  • Material & Bolt Lists
  • Reporting

A key deliverable of the works associated with the XM earthwire restringing requirement for each pull or operations to have a Construction Design Study (CDS).

Each CDS would include the full analysis of each tower, rigging arrangement, metalwork and conductor system, including the analysis of, operative weights and temporary supports.

The CDS formed the checked and approved basis of every pulling operation required for the project which was approved by the SPEN prior to issue to the site teams for use.

All routes required clearance infringement checking and mitigation. To provide an effective and efficient proposal, Groundline modelled all routes with stick models, and then when a clearance infringement required resolving through over tensioning or semi tension sets, that particular span would be modelled as required.

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