Experimental Study on Flow and Heat-Transfer Characteristics for Transformer Windings Composed of Conductors Wound with Thread Spacers. 2nd Report. Effect of Spacer Diameter Cooled by Perfluorocarbon Liquid and Air.

Abstract

In order to provide better cooling performance for transformer windings which use nonflammable coolant, conductors wound with thread spacers were applied to the windings to enlarge the cooling surface area. It was necessary to clarify the effects of the spacer diameter and different kinds of coolant on flow and cooling characteristics in the windings. Using two two-dimensional winding models, pressure drop in the windings and temperature rise of the conductors were measured for perfluorocarbon liquid and air. The two winding models consisted of model conductors in which thin heater pins and thermocouples were soldered together and wrapped in insulating paper. The conductors were also wound with two thread spacers having different diameters, 0.75mm and 0.5mm. The common frictional resistance and the heat transfer coefficient for perfluorocarbon liquid and air in vertical ducts between the conductors were derived for laminar and turbulent flow, respectively. The temperature rises for the thread spacer windings cooled by SF6 gas were predicted as being signficantly lower than those in baffle plate windings for commercial transformers with the same pressure drop in the windings.