BASIC COOLING CHARACTERISTICS OF DISK WINDINGS USING A U-BEND SUPPLY OF PERFLUOROCARBON LIQUID FOR NONFLAMMABLE TRANSFORMERS

A U-bend coolant supply was applied to transformer windings in an attempt to equalize the flow rate in the horizontal coil ducts and to cool windings uniformly. The U-bend supply, which distributes coolant equally, is used in heat exchangers. With the use of a two-dimensional winding model with ten coils, the velocity distribution in the horizontal ducts between each of two coils and the temperature rise distribution of the coils are measured for the U-bend supply and the Z-shaped supply (baffle plate type). Experiments prove that the cooling characteristics of the U-bend supply are superior to those of the Z-shaped supply at a low flow rate. Computational programs are developed for the U-bend and Z-shaped supplies to estimate flow and heat transfer characteristics in the windings. The programs accurately predict the velocity distribution in the coil ducts and the temperature rise distribution of the coils.