Browsing by Subject "Cable"

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    Characterization of Lightweight, Low-Force Cable and Hydraulic Transmission Systems
    (2022-08) Kivi, Andrew
    In the field of rehabilitation robotics and wearable exoskeletons, a common challenge forsystem designers is how to transmit force from the actuators to the joints. In small-scale applications, for the working range of 50-500 N, cables and hydraulics are the two most common ways to transmit force. This study characterized wire rope, braided synthetic line, Bowden cable, and hydraulic transmission types based on their size, weight, efficiency, and controllability. Analytical and experimental methods were used to evaluate individual aspects of each transmission. Analysis was performed to compare the transmission types. The rate at which cables increase in size and weight is approximately linearly with rated load; however, cable construction had the largest influence on the rate of increase. It was observed that cable stiffness can be fit to a 1/L model in the approximate range of 20 to 50 cm, but not for much longer lengths. Hydraulic stiffness was modeled, and it was shown for small diameter actuators the stiffness is comparable to the cables studied. Cable efficiency was studied using the capstan equation and found to be Coulomb friction dependent decreasing as wrap angle or coefficient of friction increased. Bowden cable efficiency is also friction dependent, however Bowden cables do not follow the capstan equation. Over-constrained Bowden cable paths led to more surface contact and decreased efficiency. Hydraulic transmission efficiency is dependent on hose diameter and flowrate. Optimal designs operate at high working pressures and low flowrates. It was shown in a case study that the optimal transmission type is often application dependent.
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    Parametric Evaluation of Water Treeing in EPR-Insulated Medium Voltage Cables using Finite Element Analysis
    (2021-05) O'Brien, Sean
    Medium voltage (MV) electric cables are used extensively in industrial settings, including nuclear power plants (NPPs). In NPPs, these cables provide supplementary power for safety systems to continue operating during emergency events. Despite efforts to maintain these cables, premature failure is known to occur, with the predominant causal factor being water tree-induced degradation of the cable’s insulation component. To better understand the effects of this degradation source, this thesis presents a parametric evaluation of various water tree and cable parameters using finite-element analysis (FEA). The parameters being evaluated for a MV cable insulated with ethylene propylene rubber (EPR) are water tree depth, composition, and geometry, as defined by aspect ratio (AR), and cable operating frequency and temperature. Evaluation is performed in five separate but interrelated areas pertaining to the measurement of degradation: global capacitance, global resistance, voltage and electric field distribution, localized specific energy absorption rate, and localized temperature rise. Results show that the rate of water tree-induced degradation is affected by each parameter. In general, rate of degradation was found to be directly related with water tree depth and AR, and cable temperature, but inversely related with cable operating frequency. Although values differed, these trends were largely maintained regardless of water tree composition. The results and findings of this parametric evaluation have provided an advanced understanding of water tree degradation in MV EPR-insulated cables. In addition, an argument for further use of FEA in conjunction with physical cable testing was presented, with the conclusion being that there exists a strong motivation to pair the two together.