Upgrading of a 230 kV Steel Transmission Line System Using Probabilistic Approach

The paper presents a systematic approach to the upgrading of an existing 230 kV transmission line system using probabilistic method. The line system is located on a peninsula and consists of a number of steel and wood pole lines terminated at various substations. The line system extends over a severe icing zone known for glaze icing. A system approach was used in assessing the existing line reliability. The reliability analysis provided a "trend line" for the observed rate of failure. The original design ice load was updated based on the observed failure rate over a 30-year period. To ensure that the tower fails first before the conductor, a trapezoidal conductor specially designed with extra high strength steel core was used for the upgrading project. The existing suspension towers were reused with two special dead end towers designed to accommodate the increased conductor tension due to the revised ice load. Three spans were considered in the upgrading study. The optimum upgrading option is presented for the steel transmission line system and is based on the cost risk model which used the ruling span (conductor tension) as one of the primary variables for optimization. Results show that the choice of the optimum span (tension) for upgrading the existing line system is not only sensitive to damage cost but also requires other considerations. One such criterion was to ensure that the suspension towers remaining in place were not subjected to uplift forces due to increased conductor tension under cold temperatures