Design Optimization of a 138 kV Transmission Line With Optical Phase Conductors

7 October, 2019 | White paper

Richard Maranda


Structural Engineer

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Bassem Kaabia


Structural Engineer

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This paper presents the main topics related to the detailed engineering of a 138 kV transmission line near Stewart, British Columbia. This line connects the Long Lake hydroelectric generating station to the BC Hydro network.

The paper addresses the selection process of the innovative optical phase conductor (OPPC) technology and its benefits to optimize the design and minimize the construction cost of this specific project. It is understood that this is the first time this conductor type was installed on a high-voltage transmission line in Canada.

Several firms from the following fields of expertise have joined this project and conducted detailed studies for this particular site. High wind gusts of up to 320 km/hour and radial rime ice of up to 120 mm were considered. Heavy snow creep and avalanche loads were also taken into account for the tower design. To face all these engineering challenges induced by climatic loads, the OPPC selection permits to considerably reduce the structure loads. OPPC allows for an optimization of the number of cables attached to the structures by including the optical fibre inside the conductor. Consequently, it was no longer required to install an optical ground wire (OPGW) cable. As a result, the galloping ellipse interference issue between OPGW and conductors was avoided and both towers heights and foundation sizes were reduced.

In addition, the overhead line location has its own set of constructability challenges. It crosses an 800-metre-wide river, a mountainous terrain (with elevations ranging from 50 m to 1,500 m) and several valleys. Limited access to the structure locations required a construction by helicopter for the entire project. The helicopter constraint was taken into account by a modular and optimized tower design.

Combined with an optimized design methodology, the OPPC selection in this singular project clearly demonstrates the benefits of such innovative technology in the transmission line industry for both design and constructability phases.

Note that this white paper was written in collaboration with Guillaume Vachon and it was the subject of a presentation at the CIGRE Canada 2019 Conference.

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