Browsing by Subject "Insulation"
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Item Developing a Predictive Model and Novel Imaging Technique for the Failure of Polyethylene Insulators(2019-08) Zoltek, DanielPolyethylene is the most widespread polymer used in insulative cable housings due to its low cost, high chemical resistivity and low permeability to liquids and gases. This does not mean, however, that the material is not susceptible to failure under environmental working conditions. Many techniques for monitoring both chemical and physical changes have been developed, though no attempts have been made to integrate these findings. Here, we put forth a model for the failure of polyethylene cable housings under thermooxidative conditions. This model revealed an absence of data on the monitoring of polyethylene crystalline structure during the aging process, which in part controls the insulative properties of the polyethylene. Polyethylene films (30 µm) were aged at 110°C for 24-hour periods in an oven and carbonyl content, a common aging indicator, was monitored. An ATR-FTIR crystallinity monitoring technique was developed and revealed a 3-phase change of crystalline structure upon thermal aging. To better visualize the hypothesized pore formation in the polyethylene, which follows aging, EIS was used to saturate pores with gold nanoparticles before elemental analysis and imaging with SEM. Results suggest the existence of these pores and the ability for ions to penetrate the aged films.Item Hygrothermal Performance of Residential Cantilevered Floors(2014-05) Stone, Richard ByronThis field investigation was designed to compare three insulation strategies commonly used in residential cantilevered floors. The first objective is to determine floor surface temperatures above insulated cantilever cavities, with respect to occupant thermal comfort. The second objective is to determine moisture behavior within insulated cantilever cavities, with respect to durability. The experimental set-up was installed in the cantilevered floor of an existing Minnesota home. The first six months of investigation, from mid-summer into early winter, provided data for analysis and discussion presented in this thesis. Investigation results support the view that cantilevered floor cavities open to adjacent conditioned space have warmer floor surfaces above them. Condensation and wetting in some cantilever cavities during colder weather suggests that durability risks are increased in cavities where there is air movement through the thermal insulation. Further investigation is expected to provide a more comprehensive representation of the annual hygrothermal cycle.Item Parametric Evaluation of Water Treeing in EPR-Insulated Medium Voltage Cables using Finite Element Analysis(2021-05) O'Brien, SeanMedium 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.