The Prediction of The Thermal and Hydraulic Performance of Underground Electric Transmission Systems With Turbulent Forced Convection Cooling
Ghetzler, Richard
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https://hdl.handle.net/2142/67033
Description
Title
The Prediction of The Thermal and Hydraulic Performance of Underground Electric Transmission Systems With Turbulent Forced Convection Cooling
Author(s)
Ghetzler, Richard
Issue Date
1981
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
Heat transfer and friction factors were experimentally determined in a scale model of high voltage underground transmission systems for Reynolds numbers up to 8000. Two ratios of cable to enclosure pipe were considered, corresponding to standard and oversize enclosure pipes. Helical wire wrap was included to simulate protective skid wires around the cables. Three configurations of cable positioning were considered.
A method of generalizing the heat transfer coefficients was developed and tested here for pipe cables, based on extensions of the work by Webb, Exkert and Goldstein for heat transfer in round pipes with repeated roughness elements.
Friction factors were determined experimentally for cables with up to 13 percent snaking, to simulate cable buckling due to thermal expansion. Hydraulic losses downstream of a buckled section, and through a sudden expansion at the outlet of a cable system were developed for friction factor as a function of cable snaking.
A finite difference computer code was developed to predict to steady state thermodraulic performance of full-scale pipe-type cable systems. The parameters modeled include cable conductor temperature, coolant oil temperature, oil pressure drop, DC and AC electrical heat dissipation, experimental friction factors, generalized cable and pipe wall convective-heat transfer correlations, and a simplified model of pipe wall to soil heat conduction.
A parametric study was made, with the code, of increases in current carrying capacity possible with turbulent forced cooled operation in comparison to the self-cooled, free convection mode, with application of the maximum insulation temperature and maximum pipe pressure constraints. Variables determined included maximum distance between cooling stations and pumping and cooling power required, for transmitted power up to 240 percent of self-cooled ratings.
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