Experimental Study on Flow and Heat Transfer Characteristics for Transformer Windings Composed of Conductors Wound with Thread Spacers : 1st Report, Comparison with Baffle Plate Windings

Abstract

In order to provide higher cooling performance for transformer windings which use nonflammable coolant, conductors wound with thread spacers were applied to the windings to enlarge cooling surface area. Since coolant would flow in the narrow spaces around the conductors, it was necessary to clarify the How and cooling characteristics in the thread spacer windings. Using a two-dimensional winding model, the pressure drop in the windings and the temperature rise in the conductors were measured for different heat fluxes and flow rates. The winding model consisted of model conductors in which thermocouples and thin heater pins were soldered and wrapped in insulating papers. The conductors were wound with thread spacers of 0.75 mm diameter. The temperature rises in these thread spacer windings were found to be significantly lower than those in conventional baffle plate windings. The maximum difference in the temperature rises in the windings was also small and overheating of conductors did not occur at low flow rates in the present test. The pressure drops for the thread spacer windings were predicted as being almost equal to those in baffle plate windings for commercial transformers.