The degradation of all-dielectric self supporting cables installed in high potential electro-magnetic fields.
: A theoretical and practical evaluation of optical fibre cables strung independently on overhead power transmission lines

  • Ian Lang

    Student thesis: Doctoral Thesis


    The operational life of all-dielectric self supporting (ADSS) optical fibre cables installed on high voltage over-head power transmission lines is limited by sheath degradation caused by induced electrical activity on the cable's surface. The work
    presented in this thesis describes research completed to quantify this degradation. This has resulted in a novel analysis method being developed and used to associate product testing with field trial results. The analysis is based on evaluating the magnitude of recorded electrical activity and fitting an appropriate distribution to the data to describe relative electrical arcing power.

    This innovation was possible due to the completion of a comprehensive review of the theories dealing with the generation of the electrical activity, followed by a detailed analysis. Where appropriate, worked examples are given in the thesis to demonstrate these theories. As a result of this work three proposals have been made to simplify future analyses. They are: approximating the relevant variables to span related polynomial functions, relating capacitive coupling to the space potential, and the superposition of assumed functions.

    The work is supported by results presented of extensive practical testing and simulations carried out by the author. These include analyses of the resulting cable damage, some of which has not been discriminated between in previous work. The completed analysis of tested products has also identified, previously not quantified, degradation accelerants. The work classifies these accelerants into extrinsic installation and intrinsic product factors.

    The thesis presents and reviews the implication of the electrical degradation resistance of sheaths applied to slotted-core and advance multi-loose tube (MLT) optical fibre cable designs. This has lead to the evaluation of three generations of sheath technology, which varied from low smoke compound technology, through to bimodal polyethylene. The work also identifies specific methods to limit risk to products. They include the use of pre-blended materials and the need to assure both sheath surface finish quality and cable longitudinal water blocking.

    Finally, the thesis summarises the development of new and previously investigated proposed degradation mitigation systems. Selected possible solutions were then evaluated using tests and analysis methods developed by the author, and compared with those of other notable works. This has resulted in the filing of two patents. As a result of this research a solution has been trialed and proposed to the collaborating company. This will allow optical fibre cable to be installed in high potential fields for the prescribed lifetime, overcoming previous limitations.
    Date of AwardOct 2001
    Original languageEnglish


    • Electronic circuits

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