The objective of this paper is to introduce a general model of hot-spot temperature rise calculation for the non-directed flow windings in order to explain the thermal overshoot phenomenon. The model employs heat transfer principles and hydrodynamics, in which the duct oil flow velocity is taken into account, and is validated using experimental results obtained for step changing load current on a oil natural-air natural (ONAN) cooling mode, 40 MVA transformer. The thermal overshoot phenomenon is analyzed by simulation for a 20-MVA-ONAN-cooled unit and a 40-MVA-ONAN-cooled unit.

This study investigated the impact of thermally improved spacers (TISs) on the condensation prevention and energy saving performances of residential windows. The temperature factor and total U-value were analyzed with the two-box model, by which the TISs are represented with the equivalent thermal conductivity. The results showed that the TISs could increase the temperature factor by up to 12%, and this significantly improved the condensation prevention performance. In addition, it was proved that the TIS enables the prevention of the condensation at an outdoor temperature that is 4.2 • C to 15.7 • C lower compared with the conventional spacer. Also, it was shown that the TISs reduce the total U-value by an amount from 0.07 W/m 2 K to 0.12 W/m 2 K, implying that the heat loss through the window is reduced by a rate from 2.8% to 8.2%. In addition, the results of the whole building energy simulation proved that the TISs can reduce the annual heating-energy consumption by a rate from 3.0% to 6.3%. The results were then used for the development of monographs to determine the equivalent thermal conductivity of a window spacer that can meet the performance criteria in terms of condensation prevention and energy saving.

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