scope:

PURPOSE AND SCOPE

This document forms part of a suite of documents which define National Grid's functional and performance requirements for new plant and equipment associated with electricity.

In recent years, the non-availability of large section steel angles (305x305mm) has become critical in the event where a heavy angle tower (L6) required replacing due to condition or catastrophic failure.

Furthermore, recent growth in energy demand has led utilities including National Grid to install larger conductor systems to transmit the increased power, this in turn imposes larger loads on the existing towers. The design standards and legislative requirements that govern tower design have changed over the years and compliance with these requirements should be considered and applied in an efficient and economic manner. Retrospective modifications are considered impractical.

The design of a new tower series to be operated at 400 kV and capable of carrying the maximum electrical load needed by National Grid transmission system for a new Overhead Transmission Line (OTL) is now required.

This Specification covers the requirements applicable to the design of new double circuit (DC) tower structures, to be designated 'L13' for use on new lines and for replacement of existing L6 structures.