Passive thermal management of distribution grid assets
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This thesis presents a comprehensive study into the passive thermal management of high-voltage power electronics converters for use in augmented grid assets capable of performing power routing on the electricity grid. The work has focused on the thermal transport of single-phase closed thermosiphon systems incorporating a secondary parallel flow path for cooling an additional, typically smaller, thermal load associated with the power electronics converters. Dual-loop thermosiphon passive thermal management systems were incorporated into a grounded compact dynamic phase angle regulator (GCD-PAR) that aimed to facilitate power routing and reduce line losses on the power grid. The power router utilizes power electronics that reject heat to a planar area, or cold plate, which must be cooled by an entirely passive system to comply with the minimum 30 year mean time between failures (MTBF) consistent with grid reliability requirements. This design includes a secondary-loop cooling path that utilizes the cooling oil already present in the transformer to also cool the power router. An analytical multi-physics thermosiphon model is developed that couples existing fluid dynamic and heat transfer correlations to create a description of the steady state operation of a specific cylindrical 50 kVA transformer augmented with a thermosiphon. The model is validated experimentally and found to solve for steady state baseplate temperatures under maximum load within 2°C in 0.1 seconds. The model is then modified for a specific rectilinear 1 MVA transformer augmented with three thermosiphons. The 1 MVA model is validated experimentally and found to solve for steady state baseplate temperatures under maximum load within 4 °C in 0.2 seconds. The analytical model proves to be accurate and solve quickly with various geometric configurations and thermal loads.