Development of insulating cross-arms for compact HV lattice tower structures

S.M. Rowland, R. MacLaren, I. Cotton, D. Chambers, Vidyadhar Peesapati, C. Zachariades

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    Abstract

    There are a number of economic drivers leading to an increase in transmission requirements, and this has become a major issue in the developed and developing world. Many low-cost changes such as re-tensioning existing conductors, re-conductoring, and use of flexible AC transmission systems (FACTS) can give incremental improvements. However, more radical steps are needed to get the greater increase of power transmission required. Up-rating the line voltage is an option, although this requires major spend and upgrade in associated substations and is limited by tower clearance. Clearly rebuilding lines with larger structures is also possible. In addition entirely new lines can be built to reinforce the network. Whilst the latter two solutions are attractive, they are both very costly and incur severe planning delays and uncertainty in many countries. Insulating composite-cross-arms have been deployed on overhead line power infrastructure for many years and have been seen as a route to tower compaction. Historically the weight of ceramic insulators makes them unsuitable for high voltage lattice tower cross-arm applications, however composite insulators are much lighter. Until recently a limitation to the application of composites has been the compressive buckling resistance required and traditional box-structured cross-arms have not been practical. As a result most composite cross-arms are two-dimensional and designed to move under asymmetrical load conditions, such as wire-breaks.This paper presents the development of a robust insulating cross-arm design for application on high voltage lattice towers. This uniquely provides a one-for-one replacement of the traditional steel cross-arm design, but removes the need for separate insulators. The motivation of this development are three fold: firstly to develop compact towers, secondly to provide ground clearance solutions for existing lines, and thirdly to allow increases in voltage on existing lines. Using insulating cross-arms can reduce the height of 400 kV towers by over 25%, and voltage upgrade is possible on existing towers.The mechanical and electrical design phases of the project have used FEA as a mechanical and electrical design tool. Extensive testing of the new cross-arm, including two long-term test sites, has verified the designs. The development of an appropriate testing schedule has been required, since the product is a departure from the standard approach of separating the mechanical and electrical functions of cross-arm and insulator. The proposed design has met the testing regime developed.
    Original languageEnglish
    Title of host publicationCIGRE Session 2014
    Place of PublicationParis
    VolumeSC B2-107
    Publication statusPublished - Aug 2014
    EventCIGRÉ Session 2014 - B2 - Overhead Lines
    Duration: 24 Aug 201329 Aug 2014

    Conference

    ConferenceCIGRÉ Session 2014
    CityB2 - Overhead Lines
    Period24/08/1329/08/14

    Keywords

    • Insulating cross-arm
    • ICA
    • compact tower
    • overhead line
    • compaction
    • upgrade

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