带Z型冷却通道的油浸式变压器绕组传热实验和模拟论文.doc

带Z型冷却通道的油浸式变压器绕组传热实验和模拟毕业论文 外文正文 1. Introduction Electric transformer is a key component in the transmission and distribution of electrical energy. The reliability, lifetime, performance and design of transformers are intimately related to and affected by the formation and temperature of the hottest spot in the transformer winding disks. Due to the requirement in security and reliability, the application of mineral oil as a dielectric and coolant is becoming increasingly important to transformer performance. Consequently, investigation for the hottest spot in oil transformer windings has attracted particular attention from both manufacturers and user sectors. Accordingly, IEEE Standard C57.12.00-2000 requires that the hottest spot temperature and its location be determined by either measurement or calculation method. The determination of the hottest spot location and temperature by measurement is a daunting task for working transformers because of the expense, effort and difficulty involved. From the geometrical constructions, transformer windings can be classified into two basic forms, layer and disk type. The disk-type winding with zigzag cooling duct arrangement is more popular in practice, but a difficulty arises in hydraulic and thermal predictive calculations due to complex oil fluid flow paths in it. The present study is focused on the prediction of the hottest spot temperature in this type of transformer windings. In oil transformer, the cooling oil is in practice heated in winding disks and cooled in radiators, and average winding temperature is mainly determined with oil circulation condition and temperature level. In forced oil-cooled transformer, the oil circulation condition and hence cooling capacity is mainly affected (such as OF, the oil is pumped through the transformer, with natural oil circulation in the windings), and determined (such as OD, the oil is pumped and forced through the windings), by oil pump in the circulation loop, but inappropriate