The ability of an overhead conductor to carry electric power, called the “ampacity”, is determined primarily by the thermal energy balance between the heat generated within the cable and that lost, usually by convective cooling. Heat gain is mainly by Joule heating - the conversion of electric energy into thermal energy due to conductor resistance. Convective cooling is dependent on the varying ambient conditions. Ampacity can be determined using either Static or Real-Time Thermal Rating (RTTR). Static rating uses very conservative environmental conditions, e.g. low wind speed and high temperature. It under-estimates the ampacity for much of the time, while not ensuring reliability when environmental conditions are worse than assumed. This was the case in the famous 2003 blackout over large parts of eastern North America. RTTR has the potential of fully utilizing the ampacity at any moment. RTTR is specially useful for connections to wind farms, whose power output increases with wind speed as does the ampacity. RTTR is affected by conductor geometry and, inter alia, wind velocity and direction, temperature, surface roughness, free-stream turbulence and thermal boundary condition. Accurate RTTR requires a deep understanding of overhead conductor flow dynamics and heat transfer. Our aim is to study in detail the effects of unyawed conductor geometry on flow dynamics and heat transfer at Re = 1,000 as this is typical of the applications for which the results are being used to increase RTTR accuracy and precision. The particular cable is known in the industry as a “Penguin”. This study considered two cases. The base case was a circular conductor with diameter, D, of 0.01431 m that was used to assess accuracy of the simulation and as a benchmark for the second case, the Penguin stranded conductor with the following specifications: D = 14.31mm, and helical strand diameter of 4.77 mm for the 6 helical strands. The pitch, the spanwise distance to complete one revolution divided by D, was 12.6. This was twice the span of the computational domain. Large eddy simulation employing the dynamic Smagorinsky subgrid model was used for both geometries. The results showed good agreement for the bulk flow parameters - the drag coefficient, and Nusselt and Strouhal numbers, with previous analytical, computational and experimental results. The Strouhal number was the same for the Penguin conductor and the circular cylinder. The drag was higher for the former, and there were noticeable differences in local heat transfer. In addition, differences between the flow dynamics between two cases are shown most clearly in the proper orthogonal decomposition (POD) of the fluctuating vorticity and temperature fields but less so in the POD of the turbulent kinetic energy. In addition, significant differences were found in the behavior of the coherent contribution to the streamwise heat flux.


Flow Dynamics and Heat Transfer of a Stranded Overhead Conductor Cable

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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