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Effects of various design and operating parameters on the hot-spot temperature are analyzed in disk-type forced oil-cooled transformer windings. The results indicate that a two-dimensional thermal analysis in the disks is necessary to determine the temperature and location of the hottest spot, and that the cooling oil-flow arrangement has a significant influence on the cooling of disk windings. The maximum disk temperature for each pass is proportional to the oil entrance temperature and, therefore, the heat transfer in the radiator should be improved as much as possible. A larger total oil-flow rate through the pass can increase the cooling capacity and, hence, improve the cooling of the disks, but increases the pressure loss. Although a uniform distribution of cooling oil flow among the various horizontal cooling ducts within a pass is beneficial to decrease the hottest spot temperature, the best cooling results can be obtained when the cooling flow distribution matches the distribution of heat generation in each disk of the pass.
Date of Publication: July 2006