This study focuses on efforts to characterize aging occurring in 15 kV distribution cables in a dry climate. It has been shown that similar changes can be produced by a suitably planned accelerated thermal aging testing in the laboratory. The Arrhenius equation is used for establishing the accelerated aging test parameters.( ) Different modes of statistical analysis namely analysis of variance ANOVA , Andersen-Darling test for normality, F-test, t-test are performed to validate results from accelerated aging tests with field aging.
The motivation for this project is, the cable loads depends both on the heat dissipation from the cables and the thermal environment surrounding the cables. A measuring system was built for monitoring cable currents, cable temperatures and temperatures surrounding the cable. The effect of soil temperatures surrounding the cables depending on distance from the cable duct bank, ambient air temperature and cable loads is investigated. The transient cable jacket temperature rise corresponding to any step change in cable current is also examined and discussed. The daily variation of the probe thermocouple temperatures, cable current loads and the cable jacket temperatures are evaluated. The measured results were validated using the USAmp+ cable ampacity software and the substation Energy Management System (EMS) data. The measured results helps the utility to know whether the cable jacket temperatures exceeds the maximum limits and also provides data for increasing loads in case of high demand.
Total cable loading depends on heat dissipation from the cables due to their current and the surrounding thermal environment. Cable currents, jacket temperatures, and ambient air temperatures were recorded by an underground thermocouple based data acquisition system. This allowed for the analysis o f temperature effects on the cable duct from both sources. There is interaction between the adjacent cables. A step in current corresponds to a transient response it its jacket temperature. Daily ambient air extremes correlated well with the daily current and cable jacket temperature extremes. The thermal area of influence was reduced from what was previously thought, a circle of radius loft, allowing for the tighter placement o f adjacent underground ducts. The assumed value for thermal resistance used in the software modeling was verified. Seasonal trends were obtained and used to find a temperature delay that will be used to create an overload duration chart for emergency loads.
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