Sustainability of Overhead Line Conductors and Fittings – Conductor Condition Assessment and Life Extension, Volume 1: State of the Art, Working Group B2.68

WG B2.68 has produced Technical Brochure (TB) 905 which was published in July 2023. This provides comprehensive insights into the sustainability of overhead line conductors and fittings, focusing on the condition assessment and life extension of these critical components.  It is a good educational technical brochure and is easy to read.  The Australian members of the WG were Michael Lee and John McCormack.

While there is a significant effort to build new transmission capacity for the rapidly expanding levels of renewable generation, it is important not to reduce the focus on maintenance and risk reduction for existing assets.  The increase of severe storm activity in addition to flooding and bushfires is also elevating the risk of plant failure.  In this context, a focus on the management of the ageing transmission lines has never been more important.

A number of overhead lines throughout the world and within Australia are nearing or have surpassed their expected lifespan. Since the conductors (including their installation) represent approximately 40% of the cost of the line, their condition is predominant in the decision to replace the line or extend its life after evaluating if the conductors are degraded.  This TB underscores the importance of understanding ageing mechanisms, diagnostics, tools, monitoring methods, and current asset management practices to prolong conductor life without compromising line reliability.

The TB does not focus on aluminium conductors AAAC1120.  When AAAC is referred to it is 6201A and occasionally 5005.  AAAC1120 is an improved version of AAAC1350 and has similar corrosion behaviour and will have slightly improved fatigue and improved creep.

For Australian lines the corrosion issues of coastal salt (impacting 66% of Australian lines) and moisture are important for all joints, damper clamps and other fittings.  Notably corrosion will be on the upper side of a sloping conductor.

In some locations and with certain conductor types, grease can be an important corrosion inhibitor.  Limited data in the TB shows that oil content within the grease drops with age.  This aspect needs to be tested to ensure that the grease remains effective.  Also, it is noted that grease has improved in quality and properties over the past 50 years (particularly the last 15).

High Temperature Low Sag composite conductors are discussed a little but they are not a big issue for Australia as utilities have not installed significant quantities at this stage.

This TB provides an excellent resource for assessing and maintaining overhead line conductors and fittings. 

There can be significant diversity of issues related to individual transmission lines.  TSOs must deal with this diversity and the difficulty of gaining ageing knowledge. They must make choices of replacement, extension of life, etc. even if all the desired information is not available. Volume 2 will address this difficulty as far as possible by providing asset management recommendations.

The TB is free for members and 300€ for non-members.