Thermal Modeling and Experimental Validation of Mid-Conductor Winding Cooling

Abstract

A direct cooling method for windings of electrical machines, mid-conductor winding cooling, is studied. Spaces between the wires are utilized as coolant channels, with a liquid being pumped through the winding along the length. These results in the elimination of thermal interface resistances, a high heat transfer area and heat transfer coefficient while maintaining the same cross-sectional area for the copper winding. A thermohydraulic model is made and validated to analyze the heat transfer rates and pressure drop. Validation measurements with a water-glycol mixture as coolant show that the modeled and measured pressure drop correspond within 0.07 bar and the modeled and measured winding temperature within 3 °C. When made relative to the temperature difference between winding and coolant, the deviation is equal to 12%. The validated model is used to analyze the performance when utilizing oil as coolant. For a winding temperature of 180 °C and a pressure drop of 1 bar, using the novel cooling method results in a maximal attainable current density equal to 39.4 A/mm2 which is 41% higher than that attainable with spray end winding cooling.