Case Study 25: ZZA 275kV / 400kV NGET Diversion – PROJECT ONGOING

SCOPE Transmission Diversion Design inc Contractor Works
START / COMPLETION April 22 – October 22 ‍

Sunderland City Council achieved planning permission to develop their International Advanced Manufacturing Park, and applied to National Grid Electricity Transmission to divert the existing ZZA 275kV overhead line which currently occupies the land in which the development will be located.

The overhead line operates at 275kV but the majority is constructed and fitted to be able to operate at 400kV in the future should consent be granted for that change if required.

A replacement Tower at ZZA092 will be constructed and the existing Tower ZZA092 removed. The three existing L2 towers will be removed and seven new L8c towers will be constructed.

It is also required to replace the existing conductor system on both circuits between ZZA092 and ZZA096 with 2 x 500mm2 AAAC Rubus conductors and the existing earthwire with 1 x 160mm2 (Keziah equivalent) OPGW earthwire.

As the works will be carried out under single circuit outages, a temporary diversion consisting of a temporary mast will be required. The design of tower locations, heights and span lengths has been completed with accompanied land and visual assessments, flood risk, ecological and other environmental assessments that were required for the Section 37 application.

Working with a contractor, Groundline has been tasked to provide the detailed design and temporary works solutions associated with installing the new overhead line utilising temporary masts. The tasks associated with this project include:

• Drone LiDAR
• PLS-TOWER and PLS-CADD Modelling
• Structural Analysis & Strengthening
• Temporary Works Identification
• Sag and Tension
• Stage by Stage
• Clearance Reporting and Mitigation
• Geotechnical Analysis
• Foundation Design
• Insulator Drawings
• Wire Clearance Diagrams
• Profiles
• Line Schedule
• Setting Level Diagrams
• Material Ordering Schedules
• Contractor Support
• Construction Design and Rigging Studies

During the project, it has been identified that a potential point of connection may be installed close to the line. A planned angle tower has been replaced for a DJT type tower in order to facilitate a future point of connection.

By undertaking the design for the new DJT tower, futureproofing the overhead line, limiting the amount of future works associated with dismantling and erecting new structures, reducing the environmental impact to the works and offering a more competitive solution to the customer.

As part of this project, Groundline have provided the projects: Lead Contractors Design Assurance Engineer and Contractors Design Assurance Engineer.

The ZZA project has required Groundline to work closely with a contractor and National Grid, to ensure that designs are suitably provided within the design assurance period as per the programme. The Design assurance period and National Grids processes are included in all programming works to ensure a timely, safe delivery.

This project design is ongoing.

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