Yoshito Uwano

Natural Circulating Flow and Winding Cooling Characteristics for A Self-Cooled Transformer Model Cooled by Perfluorocarbon Liquid.

To develop a new type of self-cooled transformer which uses perfluorocarbon liquid as the cooling and insulating medium, natural circulating flow characteristics of the coolant and cooling characteristics of the windings were investigated using a natural circulating loop composed of a two-dimensional winding model and a cooler. The winding model had three different configurations. Each model included model conductors in which thermocouples and thin heater pins were soldered and wrapped in insulating paper. Circulation flow rates, pressure drops and temperatures in the circulating loop and the windings were measured for different coil heat fluxes and different heights of the cooler center from the winding center. From the results, natural circulating flow characteristics of the coolant and its cooling characteristics in the windings were clarified. Furthermore, a computer program was developed to predict flow rates in the circulating loop and temperature rise of the windings. The program could also calculate pressure drops in the windings and cooler. Comparisons were made betweed experimental and calculated results, and the program gave valid predictions of flow rates in the natural circulating loop and temperature rises of coils in windings.

Basic Cooling Characteristics of Disk Windings Immersed in Perfluorocarbon Liquid for Mid-Capacity Transformers.

To develop a new type of mid-capacity transformer which uses perfluorocarbon liquid as the cooling and insulation medium, the basic flow and cooling characteristics in the windings were investigated. Three two-dimensional winding models having different horizontal and vertical duct spacings and number of coils in a section were used for the test. The models were composed of model conductors which had thermocouples and thin heater pins soldered and wrapped in insulating papers. The actual horizontal duct spacings, the horizontal and vertical temperature distributions of the windings and pressure drop were measured for each of the three models. The flow condition and winding configuration that cause overheating of the conductors were studied, and the influence of ripple or roughness of the insulating paper surface on pressure drop and heat transfer characteristics of the windings was investigated.